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Contents
1
Introduction
1
2
Damage due to lightning and surges
5
3
4
2.1 Damage statistics 2.2 Examples 2.2.1 Damage in hazardous areas 2.2.2 Damage to industrial plants 2.2.3 Damage to power supply systems 2.2.4 Damage to a house 2.2.5 Damage to aircraft and airports 2.2.6 Damage to wind power stations 2.2.7 Catastrophic damage
5 10 10 15 24 27 36 38 39
Origin and effect of surges
43
3.1 Atmospheric overvoltages 3.1.1 Direct and close-up strikes 3.1.1.1 Voltage drop at the impulse earthing resistance 3.1.1.2 Induced voltages in metal loops 3.1.2 Remote strikes 3.1.3 Coupling of surge currents on signal lines 3.1.3.1 Ohmic coupling 3.1.3.2 Inductive coupling 3.1.3.3 Capacitive coupling 3.1.4 Magnitude of atmospheric overvoltages 3.2 Switching overvoltages
45 45 48 49 56 57 58 58 59 60 61
Protective measures, standards
67
4.1 Lightning protection 4.1.1 Risk analysis, protection levels 4.1.2 External and internal lightning protection, DIN VDE 0185 Part 1, DIN V ENV 61024-1 (VDE V 0185 Part 100)
69 74 78
vi
Contents
4.1.3 Concept of lightning protection zones, DIN VDE 0185-103 (VDE 0185 Part 103) 4.1.3.1 LEMP-protection planning 4.1.3.1.1 Definition of lightning protection levels 4.1.3.1.2 Definition of lightning protection zones 4.1.3.1.3 Room shielding measures 4.1.3.1.4 Equipotential bonding networks 4.1.3.1.5 Equipotential bonding measures for supply lines and electric lines at the boundaries of the lightning protection zones 4.1.3.1.6 Cable routing and shielding 4.1.3.2 Realization of LEMP protection 4.1.3.3 Installation and supervision of LEMP protection 4.1.3.4 Acceptance inspection of LEMP protection 4.1.3.5 Periodic inspection 4.1.3.6 Costs 4.2 Surge protection for electrical systems of buildings, IEC 60364, DIN VDE 0100 4.2.1 IEC 60364-4-443/DIN VDE 0100 Part 443 4.2.2 IEC 60664-1/DIN VDE 0110 Part 1 4.2.3 IEC 60364-5-534/DIN VDE 0100 Part 534 4.3 Surge protection for telecommunications systems, DIN VDE 0800, DIN VDE 0845 4.4 Electromagnetic compatibility including protection against electromagnetic impulses and lightning, VG 95 372 4.5 Standards for components and protective devices 4.5.1 Connection components, E DIN EN 50164-1 (VDE 0185 Part 201) 4.5.2 Arresters for lightning currents and surges 4.5.2.1 Arresters for power engineering, IEC 61643-1/E DIN VDE 0675 Part 6 4.5.2.1.1 Important data for arrester selection 4.5.2.1.2 Coordination of the arresters according to requirements and locations 4.5.2.1.3 N-PE arrester, E DIN VDE 0675 Part 6/A2 4.5.2.2 Arresters for information technology, IEC SC 37A/E DIN VDE 0845 Part 2 4.5.2.2.1 Important data for arrester selection 4.5.2.2.2 Arrester coordination according to requirements and locations 4.5.2.3 Arrester coordination
79 83 83 83 84 90 92 94 97 99 100 101 101 103 104 105 109 110 112 112 113 113 113 119 120 121 122 124 125 125
Contents
5
Components and protective devices: construction, effect and application 5.1 Air terminations 5.2 Building and room shields 5.3 Shields for lines between screened buildings 5.4 Shields for cables in buildings 5.5 Optoelectronic connections 5.5.1 Optical fibre transmission system 5.5.2 Optocoupler 5.6 Equipotential bonding 5.7 Isolating spark gaps 5.8 Arresters 5.8.1 Arresters for power engineering 5.8.1.1 Surge arresters for low-voltage overhead lines, class A 5.8.1.2 Lightning current arresters for lightning protection equipotential bonding, class B 5.8.1.3 Surge arresters for protection of permanent installation, class C 5.8.1.4 Surge arresters for application at socket outlets, class D 5.8.1.5 Surge arresters for application at equipment inputs 5.8.1.6 Application of lightning current arresters and surge arresters 5.8.1.6.1 Graded application of arresters, energetic coordination between surge arresters and equipment to protect 5.8.1.6.2 Application of arresters in different system configurations 5.8.1.6.3 Selection of arrester backup fuses 5.8.2 Arresters for information technology 5.8.2.1 Arresters for measuring and control systems 5.8.2.1.1 Blitzductor®CT: Construction and mode of functioning 5.8.2.1.2 Blitzductor®CT: Selection criteria 5.8.2.1.3 Blitzductor®CT: Examples of application 5.8.2.1.4 Arresters for intrinsically safe measuring and control circuits and their application 5.8.2.1.5 Arresters for cathodic protection systems 5.8.2.1.6 Arresters in Euro-card format 5.8.2.1.7 Arresters in LSA-Plus technology 5.8.2.2 Combined protective devices for power supply inputs and information technology inputs
vii
127 127 129 138 141 143 144 145 145 150 153 155 155 157 167 174 175 175 178 182 196 206 209 210 223 228 238 246 248 248 253
viii
Contents
5.8.2.3 Protective devices for data networks/systems 5.8.2.3.1 Protective devices for application-neutral cabling 5.8.2.3.2 Protective devices for token ring-cabling 5.8.2.3.3 Protective devices for Ethernet twisted paircabling 5.8.2.3.4 Protective devices for Ethernet coax-cabling 5.8.2.3.5 Protective devices for standard cabling 5.8.2.3.6 Protective devices for data telecontrol transmission by ISDN base terminal 5.8.2.3.7 Protective devices for data telecontrol transmission by ISDN primary multiplex terminal 5.8.2.3.8 Protective devices for data telecontrol transmission by analogous a/b-wire terminal 6
7
255 255 262 265 267 271 277 284 286
Application in practice: Some examples
293
6.1 Industrial plants 6.1.1 Fabrication hall 6.1.2 Store and dispatch building 6.1.3 Factory central heating 6.1.4 Central computer 6.1.5 European installation bus (EIB) 6.1.6 Other bus systems 6.1.7 Fire and burglar alarm system 6.1.8 Video control system 6.1.9 Radio paging system 6.1.10 Electronic vehicle weighbridge 6.2 Peak-load power station 6.3 Mobile radio systems 6.4 Television transmitter 6.5 Mobile telecommunication facility 6.6 Airport control tower
295 295 296 302 307 309 313 313 316 318 320 323 328 334 339 343
Prospects
351
Index
353
Chapter 1
Introduction
Business, industry and public institutions depend on electronic data engineering. Electronic data processing (EDP) systems, measuring and control systems, instrumentation and control as well as secondary technology are all part of a modern industrial plant. Data recording devices at the production facilities are connected to office terminals and computers by information networks ranging between buildings—together making CIM (computer integrated manufacturing). Open networks, where different types of computers and different operating systems communicate, are often the basis for CIM. This rapidly expanding business process is now approaching the CIE (computer integrated enterprise) or CIB (computer integrated business); in other words, the complete integration of all ranges of administration into a multi-EDP system. The future lies in the computer-integrated factory or in computer-integrated business and administration. Everywhere, computers in local banks are connected to the computing centre of the main bank. This ‘networked’ world, with its growing flow of information, is, however, severely hindered by interference or damage to the essential transmission systems in the telephone and data networks, as well as at terminals (Figure 1 a). Dependence on electronic data processing can quickly lead to catastrophe if the system fails. An American study in 1987 highlighted the seriousness of the situation. According to this, banks will only be able to manage without EDP for 2 days, sales-oriented enterprises will be able to manage for 3.3 days, manufacturers for 4.9 days, and insurance companies for 5.6 days. An investigation by IBM Germany disclosed that enterprises without functioning EDP would be on the verge of ruin after about 4.8 days. In many business sectors within the European Market this risk will certainly continue to increase in the future. Computer safety experts point out that nine out of ten enterprises will close if the computer fails for two weeks. The most frequent reason for
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Overvoltage protection of low voltage systems
Figure 1 a
Partial lightning currents propagate on lines and mains
the failure of such electronic systems is transient electromagnetic interferences that disturb the flow of data and destroy electronic equipment. Risk can be controlled by electromagnetic compatibility (EMC) measures. This specifies conditions under which any kinds of electric equipment do not disturb each other and also where electromagnetic phenomena, for example, lightning discharges, will not disturb their function. The European Community has declared EMC as a protection goal by issuing the ‘Richtlinie des Rats vom 3. Mai 1989 zur Angleichung der Rechtsvorschriften der Mitgliedstaaten über die Elektromagnetische Verträglichkeit’ (Council Directive of 3 May 1989 to Harmonise Laws of the Member Nations concerning Electromagnetic Compatibility). All apparatus, facilities and systems that include electric or electronic components must demonstrate sufficient ‘withstand’ levels against electromagnetic disturbances to guarantee proper operation of equipment. The instructions of the Council especially mention the following facilities: industrial equipment, telecommunication networks and equipment, mobile radio sets, information technology equipment, private sound and TV-radio-receivers, commercial mobile radio and radio-telephones, medical and scientific apparatus and equipment, household appliances and electronic household equipment, radio sets for navigation, electronic education gear, transmitters for radio and television, and luminaires and fluorescent lamps. These instructions were transferred into German law on 9 November 1992 as the ‘Gesetz über die Electromagnetische Verträglichkeit von Geräten (EMVG)’ (Law on the Electromagnetic Compatibility of Devices (EMCD)) and was fully valid as from 1 January 1996. A change to the EMVG was made on 30 August 1995. Violation of the EMC law, and thus of the EMC general instructions, is deemed a summary offence. Among the threats from the electromagnetic environment, lightning discharge (Figure 1 b) is the most important and therefore this deter-
Introduction
3
Figure 1 b Lightning discharge – a special electromagnetic source of interference
mines to a great extent the protective measures that must be undertaken in the framework of EMC. Therefore, modern lightning protection does not only mean protection of buildings but especially the protection of those devices covered by Section 2, item 4 of EMVG, meaning that a lightning protection system also must be erected, even if it is not necessary for the building, for the equipment it contains, in the sense of Section 2, item 4 of EMVG. This book presents proven lightning and surge protection measures, taking into account the latest standards and engineering. The components and devices that are used to achieve these protective measures are explained in terms of their function and application by means of practical examples.
Sources SACHSE, CH.: ‘Computersicherheit – Tanz auf dem Vulkan’ (ManagementWissen, 1987) No. 6, pp. 68–72 PIGLER, F.: ‘EMV und Blitzschutz leittechnischer Anlagen’ (Siemens AG, Berlin u. München, 1990) SCHWAB, A. J.: ‘Elektromagnetische Verträglichkeit’ (Springer Verlag, Berlin, Heidelberg, New York, 1990) BEIERL, O.: ‘Elektromagnetische Verträglichkeit beim Blitzeinschlag in ein Gebäude’ (Fortschrittsberichte VDI, 1991) Reihe 21, Nr. 93 (VDI-Verlag GmbH, Düsseldorf) KOHLING, A.: ‘EG-Rahmenrichtlinie und Europäische Normen zur EMV’, etz Elektrotech. Z., 1991, 12, (9), pp. 438–441
4
Overvoltage protection of low voltage systems
GONSCHOREK, K.-H. and SINGER, H.: ‘Elektromagnetische Verträglichkeit’ (B. G. Teubner, Stuttgart–Leipzig, 1992) HABIGER, E.: ‘Elektromagnetische Verträglichkeit. Grundzüge ihrer Sicherstellung in der Geräte- und Anlagentechnik’ (Hüthig Buchverlag GmbH, Heidelberg, 1992) HABIGER, E.: ‘Handbuch Elektromagnetische Verträglichkeit’ (Verlag Technik GmbH, Berlin–München, 1992) MEYER, H. (Ed.): ‘Elektromagnetische Verträglichkeit von Automatisierungssystemen’ (VDE-Verlag, GmbH, Berlin/Offenbach, 1992) DIN VDE 0870 Teil 1: ‘Elektromagnetische Beeinflussung (EMB)’ Begriffe. (VDE-Verlag, GmbH, Berlin/Offenbach, July 1984) Richtlinien des Rats vom 3 May 1989 zur Angleichung der Rechtsvorschriften der Mitgliedstaaten über die Elektromagnetische Verträglichkeit (89/336/ EWG). Brüssel: Amtsblatt der Gemeinschaft L 139/19 (23 May 1989) Gesetz über die Elektromagnetische Verträglichkeit von Geräten (EMVG), 9 Nov. 1992. Bundesgesetzblatt Teil 1, Nr. 52 (12 Nov. 1992) Erstes Gesetz zur Änderung des EMVG vom 30 August 1995 (1. EMVG ÄndG). Bundesgesetzblatt Teil 1. Nr. 47 (8 Sept. 1995). ‘Guidelines on the Application of Council Directive 89/336/EEC of 3 May 1989 on the Approximation of the Laws of the Member States Relating to Electromagnetic Compatibility’ (Directive 89/336/EEC Amended by Directives 91/263/ EEC, 92/31/EEC, 93/68/EEC, 93/97/EEC) SCHNITZLER, J.: ‘Rechtliche Aspekte für Planer, Errichter und Prüfer von Blitzschutzanlagen’. 2. VDE/ABB-Fachtagung (6–7 Nov. 1997) Neu-Ulm: Neue Blitzschutznormen in der Praxis
Chapter 2
Damage due to lightning and surges
Damage to electronic installations is increasing due to the following factors: (i) the increasing use of electronic equipment and systems, (ii) the lower signal levels, which means higher sensitivity, and (iii) the increasing use of networks that cover large areas. Although the concomitant destruction of electronic components is not often spectacular, interruptions to operations in most cases are rather long. Thus, the consequential damage is often considerably higher than the damage to the hardware (Figure 2 a).
2.1 Damage statistics One important electronic insurance company in Germany reported that the costs of compensation for surge damage due to electromagnetic
Figure 2 a
Computer board damaged by lightning surges
6
Overvoltage protection of low voltage systems
disturbances on electronic systems and equipment, such as communication systems, computers, measuring devices and medical appliances, have quadrupled within a period of ten years (Figure 2.1 a). In 1984 8.5% of all damage adjustments were caused by surges. In 1993 34.6%, in 1994 35.5%, in 1995 33% out of 11 000 cases of damage and in 1996 26.6% and in 1997 31.68% out of 8722 cases of damage were caused by surges (Figure 2.1 b).
Figure 2.1 a
Development of the percentage of damage due to surges compared with the total damage sum (Source: Württembergische Feuerversicherung AG, Stuttgart)
Figure 2.1 b
Electronics sector: damage in 1997 (analysis of more than 9600 cases of damage)
Damage due to lightning and surges
7
In the former Federal Republic of Germany (FRG) in 1990, damage costs to electronic equipment and systems caused by surges may have exceeded one billion DM. Surge damage analysis has shown that lightning discharges are the dominant disturbances, followed by those due to switching operations in power technical systems. There are also dangers caused by electrostatic discharge. A statistic concerning lightning damage published for many years by the Upper Austrian fire prevention authority (Table 2.1 a) shows (additionally to the damage due to direct lightning strikes), indirect damage caused by electromagnetic lightning disturbances. Such indirect Table 2.1 a
Damage statistics of the Fire Prevention Authority, Upper Austria
8
Overvoltage protection of low voltage systems
damage costs are far higher than those due to direct lightning. For example, in 1993 there were 23 646 indirect damage incidents amounting to 86.2 million ÖS (Austrian schillings), compared to 64 direct damage incidents for which 27.4 million ÖS had to be compensated. There is now worldwide agreement that the danger radius around a point struck by lightning is about 2 km (Figure 2.1 c, a). Within this domain electronic systems are affected by conducted and radiated disturbances that may cause destruction (Figure 2.1 c, b). In the case of an electro-
Figure 2.1 c
(a) Lightning discharge hazard 2 km around the strike point
Figure 2.1 c
(b) Electronic systems are interfered with or damaged by conducted and radiated interference
Damage due to lightning and surges
9
magnetic disturbance by lightning, the hardware damage is only a small part of the total impact. Consequential damage, such as factory standstill due to the breakdown of computer systems or pollution due to the failure of measuring and control systems in chemical plants, causes the greatest proportion of the total loss, to say nothing of the possible liabilities. Insurers only compensate for hardware damage, and today they usually pay for the damage only if it is a first event. Thereafter, they will demand installation of protective measures according to the level of standardization and engineering technology, otherwise they will cancel the insurance contract (Figure 2.1 d). It is a usual condition for the
Figure 2.1 d
Text of a letter from the Liability Insurance Association of the German Industry concerning ‘surge damage’
10
Overvoltage protection of low voltage systems
conclusion of new contracts that proof of existing relevant protective measures be supplied.
2.2 Examples Some examples of damage due to lightning discharge, switching operations or electrostatic discharge now follow.
2.2.1 Damage in hazardous areas The disastrous consequences of lightning strikes in hazardous areas will be illustrated by the following five examples. In 1965 a 1500 m3 solid-roof petrol tank in the DEA-Scholven refinery in Karlsruhe was struck by lightning. The tank exploded and burnt out completely (Figure 2.2.1 a). Figure 2.2.1 b shows the measuring equipment inside the tank. The ohmic resistance of a nickel spiral with float serves for measuring the temperature in the tank. As lightning struck the tank there was a flashover from the tank to the wires of the measuring cable which had the potential of the ‘remote’ earth. The explosive mixture was struck and the tank burnt out. A similar remarkable case happened ten years later in the Netherlands. A 5000 m3 kerosene tank exploded due to a lightning strike (Figure 2.2.1 c). The inner tank temperature was controlled by a thermoelement connected to the control room by a 200 m long measuring cable which also had, as in the above-mentioned case, the ‘remote’ earth potential. As
Figure 2.2.1 a
Burned out tank due to a lightning strike, Karlsruhe, 1965 (Source: DEA-Scholven, Karlsruhe)
Damage due to lightning and surges
11
Figure 2.2.1 b
Measuring equipment to determine the temperature inside the tank
Figure 2.2.1 c
Lightning strike to a kerosene tank, Netherlands, 1975
one of the surrounding willow trees was struck by lightning, there was a discharge from the roots of the tree to the earthing system of the tank. The potential of the tank system increased in accordance with its impulse earthing resistance. As a consequence, there was a sparkover to the measuring line and due to this open sparkover, the kerosene-air– mixture caught fire. An amateur photographer shot pictures of this lightning strike and the following explosion (Figure 2.2.1 d). A lightning strike with severe consequences also happened in a chemical plant in Herne in August 1984 where an alcohol tank burnt out (Figure 2.2.1 e). Here, TÜV experts managed to find out the reason for
12
Overvoltage protection of low voltage systems
Figure 2.2.1 d
(a)
Figure 2.2.1 d
(b)
Figure 2.2.1 d (a, b) 250 m high explosion cloud after the lightning strike to a kerosene tank (Source: Brood, T.G.P.)
Figure 2.2.1 e Burning alcohol tank due to a lightning strike, Herne, 1984 (Source: Kartenberg, H. J.)
Damage due to lightning and surges
13
the damage. Once again it was a measuring cable entering the tank with the potential of the ‘remote’ earth that led to the burn out. In October 1995 lightning struck the Indonesian oil refinery Pertamina in Cilacap on the south coast of Java. The tank exploded and the burning oil set fire to six neighbouring tanks (Figures 2.2.1 f and g). Again the reason was incomplete equipotential bonding. Thousands of Cilacap inhabitants and 400 Pertamina employees had to be evacuated for their safety. There was a standstill for about 18 months for this refinery which supplied 34% of Indonesia’s inland need. This meant that oil, petrol, kerosene and diesel, worth about DM 600 000, had to be imported daily for the supply of Java. Only in Spring 1997 was the company able to restart its own production. In June 1996 a lightning strike in New Jersey, USA, set fire to petrol tanks containing 300 000 gallons of petrol. About 200 people had to be evacuated (Figure 2.1 h). The reasons for these cases of damage are indicated as shown in Figure 2.2.1 i. Lightning hits an almost closed Faraday cage which has a hole. A line coming from a distant building and which is earthed there enters this hole. Between the lightning-struck Faraday cage and this ‘remote’ earth a voltage drop develops that is caused by the lightning current at the impulse earth resistance (e.g. in Figure 2.2.1 i, 100 kV). Conventional measuring line insulations, however, can only withstand impulse voltages of some 100 V; higher values will cause punctures with arcing.
Sources v. THADEN, H.-W.: ‘Tankbrand durch Blitzeinschlag’ (Erdöl u. Kohle-ErdgasPetro-chemie, 1966), pp. 422–424 BROOD, T. G. P.: ‘Bericht über infolge Blitzeinschlag verursachte Brände in zwei geschützten Tanks für die Lagerung von brennbaren Flüssigkeiten’. 13. Intern. Blitzschutzkonf., Venedig (1976), Referat R-4.5 WESTDEUTSCHE ALLGEMEINE ZEITUNG: ‘Herner Tank-Unglück – Blitzschlag trotz einer Schutzanlage’ (4 Dec. 1984) THE JAKARTA POST: ‘Cilacap fire won’t affect domestic fuel oil supplies’ (26 Oct. 1995) THE NEW YORK TIMES: ‘Lightning starts fuel tank fire in New Jersey’ (12 June 1996) SIRAITI, K. T., PAKPAHAN, P., ANGGORO, B., SOEWONO, S, ISKANTO, E., GARNIWA, I., and RAHARDJO, A., ‘An analysis of origin of internal sparks in kerosene tank due to lightning strikes’. Lightning and Mountains ’97, June 1997, Chamonix Mont Blanc/France ZORO, R., SUDIRHAM, S., and SASONGKO, D. (ITB Bandung, Indonesia): ‘Kerosene tank explosions due to lightning strikes in an Indonesian refinery plant’. Lightning and Mountains ’97, June 1997, Chamonix Mont Blanc/ France
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Overvoltage protection of low voltage systems
Figure 2.2.1 f, g
Oil refinery Pertamina, Cilacap/Java, 1995. Seven tanks burned out due to a lightning strike
Damage due to lightning and surges
Figure 2.2.1 h
15
Lightning strike sets petrol tank on fire, New Jersey, USA, 1996
2.2.2 Damage to industrial plants Repeated and extensive surge damage was caused to Europe’s largest computer-controlled lorry factory, Daimler–Benz AG, at Wörth, near Karlsruhe. Often the production came to a standstill and, correspondingly, extended production losses resulted from both direct and remote lightning strikes. The factory halls are on a site with a length of 1.5 km and a width of 1 km. In two shifts, 10 000 workers produce 400 lorries per shift. The material stock computers are connected with those in production control by a DC data transmission system; this digital symmetric transmission system works at ±350 mV. At the beginning of the 1980s, surges repeatedly damaged the linked equipment, each time bringing with it a complete production standstill.
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Overvoltage protection of low voltage systems
Figure 2.2.1 i
Lightning strike to the Faraday cage causes flashover to the line at the ‘Faraday hole’
In a textile mill in the former GDR the fire alarm system was activated by the ionization detector following a lightning strike on the roof of a high-bay warehouse. This activated the automatic sprinkler system. Consequential water damage was about 1 million DM. The warehouse was only equipped with an ‘external lightning protection system’. A lightning strike to the roof was also the reason for a production standstill in the cutting department of a ready-made clothes manufacturer in Dresden, in 1989. Here the central computer and machine control were disturbed by the 80 m long data cable. The so-called ‘external lightning protection system’ could not prevent this damage; ‘internal lightning protection’ measures were absent. Systems with cables and lines crossing several buildings are especially endangered. In the Leuna works, in 1989, thunderstorms caused a failure of electronic control and supervision equipment causing a standstill in production. Distributed sensors in the process system were connected with the control room by cables the shields of which were bonded with the equipotential bonding bar of the control room. Complete lightning protection equipotential bonding, however, had been neglected and only a few special cables were connected with protective diodes. The damage loss exceeded 1 million DM. A lightning occurrence in 1983 will now be described due to its particular characteristics. The conclusions that are drawn are valid even today. The case entails the administration tower of Klöckner– Humboldt–Deutz in Cologne (Figures 2.2.2 a and b). This was struck by lightning that was diverted to earth by the ‘external lightning protection system’. Because of the absence of an ‘internal lightning protection
Damage due to lightning and surges
Figure 2.2.2 a
17
Lightning strike into the administration building of Messrs KHD, Cologne, 1983
system’, about 100 terminals (Figure 2.2.2 c) and numerous computer processors (Figure 2.2.2 d) in the computer centre (about 120 m away) were disturbed by this strike (Figure 2.2.2 e). Hardware damage alone amounted to 2 million DM; the consequential loss due to the nonavailability of the computer systems was about 4 million DM. During this particular thunderstorm other neighbouring industrial plants had surge damage to their computers, telephone and telex systems. The reasons for these types of damage can be explained by considering Figure 2.2.2 f. If lightning strikes building 1 , a partial lightning current will flow into building 2 only because of the resistive coupling (Section 3.1.3 (a)) and thus cause damage there. Microelectronic components and circuits can also be destroyed by electrostatic discharge (Figures 2.2.2 g). False tripping of common ‘residual current circuit breakers’ (RCCB) due to electromagnetic interference at lightning discharge in close surroundings can occur. Reports such as: ‘Numerous animals killed because of an indirect lightning strike. In an intensive animal breeding farm 14 000 chickens suffocated as the ventilators failed because of false tripping of a residual current circuit breaker, after an indirect lightning strike’ are not unusual. It must be explained that in intensive chicken breeding farms about 15 000 chickens are reared within six weeks on a surface area of about 1000 m2 (Figure 2.2.2 h). During this period, the birds are fed automatically. But, besides food and water, the continuity of air supply (Figure 2.2.2 i) is of obvious vital importance. If, for example, the ventilation system is shut down by false tripping of the
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18
Overvoltage protection of low voltage systems
Figure 2.2.2 b
Administration building behind the computing centre (Messrs KHD)
Figure 2.2.2 c
Computer terminals in the administration building (Messrs KHD)
Damage due to lightning and surges
Figure 2.2.2 d
Computing centre (Messrs KHD)
Figure 2.2.2 e
Computer PCB damaged by lightning surge
19
20
Overvoltage protection of low voltage systems
Figure 2.2.2 f
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At a lightning strike to building 1 : Surge damage in buildings 1 and 2
䊊 䊊
Figure 2.2.2 g (a)
Figure 2.2.2 g (b) Figure 2.2.2 g
(a, b) MOS module damaged by electrostatic discharge. (Source: 3M Deutschland GmbH, Neuss)
Damage due to lightning and surges
Figure 2.2.2 h
Automatic feeding
Figure 2.2.2 i
Ventilator in an intensive animal breeding building
21
22
Overvoltage protection of low voltage systems
corresponding residual current circuit breaker, the chickens will suffocate within 20 minutes. In 1987 a defect was to occur in the 20 kV cable network of the town Neumarkt while several switching operations were made. This gave rise to switching surges in the 220/380 V system, leading to flashover with damaging arcs in the reactive-current compensation system of the local abattoir (Figures 2.2.2 j). There were several instances of damage of up to 70 000 DM each in a combined building services and access control system with about 300 interconnected individual components. In the parts of the building affected, the automatic access control only functioned after several days of repair. In each of these cases the reason was a surge ‘incoupling’ into external components, like code card scanners, due to lightning. All external components of the control system are connected to a central computer by station computers and bus connections. The printed boards of the station computers and bus couplers were thus damaged by the incoupling of the surges (Figures 2.2.2 k, a and b). A loss of about 100 000 DM occurred as surges damaged the printed boards of a printing press (Figure 2.2.2 l, a), (Figure 2.2.2 l, b). For this production phase this was the only machine available (maximum capacity machine). A longer standstill of production, due to some difficulties in obtaining spare parts for this machine, caused problems in delivery and a great loss of income. The reason for the defective machine
Figure 2.2.2 j
Figure 2.2.2 j
(a)
Figure 2.2.2 j
(b)
(a, b) Reactive current compensation system in a slaughter house damaged due to switching surges, Neumarkt, 1987
Damage due to lightning and surges
Figure 2.2.2 k (a) Damaged interface card
23
Figure 2.2.2 k (b) Damaged bus coupler
Figure 2.2.2 k
(a) and (b) Surge damage in a building services control system
Figure 2.2.2 l
(a) Surge damage at a printing press
was a cable fault in the 20 kV power supply system, causing surges in the low-voltage system.
Sources HASSE, P., and PRADE, G.: ‘Das Auslöseverhalten von FI-Schutzschaltern bei Gewittern. de/der elektromeister + deutsches elektrohandwerk’, 4 (1980), pp. 203–207
24
Overvoltage protection of low voltage systems
Figure 2.2.2.l
(b) Damaged module of the printing press control
GUGENBAUER, A.: Blitze–Feuerzauber der Natur. die österreichische feuerwehr (1983) H. 7 HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatz elektronischer Geräte auch bei direkten Blitzeinschlägen. 3. aktualisierte Auflage’ (Verlag TÜV Rheinland, Köln, 1993) DAUSEND, A.: ‘Überspannungsschutz als Teil des betrieblichen RiskManagements’ Teil II: Schadenfälle aus der Praxis. In: HASSE, P. (Ed.): 5. Forum für Versicherer ‘Blitz- und Überspannungsschutz – Massnahmen der EMV’ (Dehn + Söhne, Neumarkt, 1994)
2.2.3 Damage to power supply systems The public is alarmed sometimes by reports of lightning strikes to power supply systems or even nuclear power stations. In 1983 lightning struck the 110/20 kV transformer substation of the town Neumarkt (Figures 2.2.3 a and b). There was considerable damage to the switching station and a failure of the 220 V direct voltage control. The 20 kV surge arresters were already damaged by the initial partial lightning strikes (Figure 2.2.3 c) and, thus, the subsequent lightning strikes could no longer be discharged. Sparkover arcs occurred in one switchbay (Figure 2.2.3 d) which ran along the bus bar and damaged other switchbays. Further shortcircuit arcs were generated on the 20 kV overhead lines. Heavy conductor rope vibrations made the ropes glow and tear. To add further to the problems, the supplying 110 kV transformer exploded during this thunderstorm (Figure 2.2.3 e) with the consequence that the whole town of Neumarkt (about 30 000 inhabitants) lost power for about six hours.
Damage due to lightning and surges
Figure 2.2.3 a
Transformer substation 110/20 kV, OBAG, Neumarkt
Figure 2.2.3 b
Site plan of the transformer substation 110/20 kV, OBAG, Neumarkt
25
26
Overvoltage protection of low voltage systems
Figure 2.2.3 c
Surge arresters destroyed by lightning strike
Figure 2.2.3 d
Damage in 20 kV switching bays due to lightning surge
Damage due to lightning and surges
27
Figure 2.2.3 e Exploded 110 kV transformer due to lightning strike, Neumarkt, 1983
Sources DER SPIEGEL: ‘Blitz im Atommeiler’ (1983) No. 36, p. 15 NEUMARKTER TAGBLATT: ‘Kurzschluss in Kernkraftwerk’ (22 May 1985)
2.2.4 Damage to a house Lightning strikes into unearthed aerials of houses (without lightning protection systems), such as the family house in Figure 2.2.4 a, occur frequently. Figures 2.2.4 b to h show the damage caused by lightning current
28
Overvoltage protection of low voltage systems
Figure 2.2.4 a
Site plan of a house damaged by lightning, Neumarkt, 1986
Figure 2.2.4 b
Damage near the antenna-pole in the loft, Neumarkt, 1986
on its path of sparkovers and punctures through the electrical wiring of the house. The lightning current flows over the aerial standpipe (Figure 2.2.4 b), feeding partial lightning currents into the power system, aerial line, telephone line and water pipe. So, usually, all connected electrical appliances and the telephone system will be damaged. In the case mentioned, the fuel oil pipe was also damaged, and oil leaked into the cellar. In a circle of radius more than 1 km, telephone systems failed due to this lightning strike; the traffic-light systems of the town were also disturbed and RC circuit breakers were tripped within a radius of about 3 km.
Damage due to lightning and surges
(a) Neumarkt 1986 Figure 2.2.4 c
(b) Similar case
Punctures to concealed cables due to lightning strike
(a) Neumarkt 1986 Figure 2.2.4 d
29
(b) Similar case
Antenna line damaged by lightning strike
In 1994, during a thunderstorm burst, the radio aerial of a central taxi station in Neumarkt was struck by lightning (Figure 2.2.4 i). The whole radio system was destroyed (Figure 2.2.4 j). The electrical cables and socket outlets were torn out of the walls and the entire electrical equipment (TV and household appliances) was damaged so heavily that it could no longer be used.
30
Overvoltage protection of low voltage systems
(a) Neumarkt 1986
(b) Similar case Figure 2.2.4 e
(c) Similar case
Distribution cabinets damaged by lightning strike
Damage due to lightning and surges
Figure 2.2.4 f Boiler damaged by lightning strike, Neumarkt, 1986
Figure 2.2.4 h Puncture from the power line to the metal oil pipe due to lightning strike, Neumarkt, 1986
31
Figure 2.2.4 g Telephone system damaged by lightning strike, Neumarkt, 1986
Figure 2.2.4 i
(a)
Figure 2.2.4 i
(b)
Figure 2.2.4 i
(a, b) Lightning strike to the Lutter taxi central office, Neumarkt, 1994
32
Overvoltage protection of low voltage systems
Figure 2.2.4 j
Damaged radio system
Figure 2.2.4 k Damaged electrical lines
A pressure wave smashed windows and window frames. Tiles were torn off the wall and there were cracks in the ceilings and the walls. Socket outlets were torn out of the wall (Figure 2.2.4 k). Partial lightning currents were conducted along the telephone system and the power supply system, thus causing other damage in the neighbourhood (Figure 2.2.4 l). In the vicinity and wider surroundings this lightning strike caused considerably more damage than listed here. In the office of the District President, the district hospital, the inferior court, the municipal works and the abattoir, as well as in industrial and commercial enterprises, the computer systems and telephones were damaged. In the district hospital, a church, an elementary school and a museum, the safety and fire alarm systems were damaged (Table 2.2.4 a). In Figure 2.2.4 m, circles are drawn, at a separation of 1 km, around the lightning striking point (marked by an arrow). The locations of the damage are marked by bullets. Damage occurred, even at a distance of 3 km from the point of strike, for example, in the traffic-light system at the southern perimeter road of the town. The Neumarkter Nachrichten duly reported on the damage caused to telephone and cable television connections in 40 households and numerous individual TV sets. Repeatedly, there are extended disturbances in telecommunication sectors due to solitary lightning strikes. The Hamburger Abendblatt of 12 July 1995 reported on a thunderstorm two days previously when 25 000 Telecom customers in the suburbs of Hamburg were concerned by failures of cable TV. Some 50 microchip amplifiers had to be repaired in Pinneberg, Wedel, Quickborn and Norderstedt. Underground cables damaged by lightning currents reveal high interference energies.
Damage due to lightning and surges
Figure 2.2.4 l
33
Lightning damage (at Telekom systems) in the surroundings of the point of strike
The reason for the above examples of damage is that electrical lightning interferences are conducted through power and data lines from the point of strike over distances of several kilometres directly to the inputs of electronic systems and equipment (Figures 2.1 c and 2.2.4 n). Telephone systems, for example, are used in data processing and alarm systems, making them susceptible.
Sources NEUMARKTER NACHRICHTEN: ‘Blitzschlag zerfetzte Leitungen und hob den Dachstuhl’ (2–3 Aug.1986) NEUMARKTER NACHRICHTEN: ‘Unheil mit einzigem Blitzschlag’ (3 May 1994) HAMBURGER ABENDBLATT: ‘Kabelfernsehen: Vom Blitz getroffen’ No. 160 (12 July 1995)
34
Overvoltage protection of low voltage systems
Table 2.2.4 a
Consequences of a lightning strike to the Lutter Taxi Company Neumarkt, 1994
Damage due to lightning and surges Table 2.2.4 a
Figure 2.2.4 m
35
continued –
Lightning damage in a radius of 3 km around the point of strike
36
Overvoltage protection of low voltage systems
Figure 2.2.4 n
Dangerous surges in neighbouring buildings
2.2.5 Damage to aircraft and airports The following report from the Kölnischen Rundschau of 12 November, 1987, for example, describes the damage due to a lightning strike to an airliner: “Immediately after take-off, the Boeing 747 flying to Newark (New Jersey) entered a thunderstorm zone. Within a few minutes, four lightning discharges struck the plane with 225 passengers and 18 crew members on board. Autopilot, weather radar and the radio connection to the tower were knocked out. Also the manual control of the elevator was damaged so strongly that the pilot and copilot had to use their whole strength to keep the Jumbo flying. A British Airways jet flying in the same space followed the distress call of the struck Boeing and piloted it on the correct glide path to the emergency landing. After touchdown, Captain Richards – a former Phantom fighter pilot and Vietnam veteran – stated that the braking thrust reversal of the four engines had also failed. Only the landing gear brakes still worked. The plane was brought to a standstill a few metres before the end of the runway. Later, in the Continental repair hangar, more than a hundred instances of fire damage to the shell and wings of the Jumbo were counted. Parts of the tail fin were missing. Chief pilot Fred Abbott told: ‘I never saw a plane that was damaged so heavily by lightning.’ ”
There are reports from the Public Information section of the German Federal Ministry of Defence in January 1986 of an electrostatic accident involving a rocket: “The fire accident with a Pershing II motor stage happened on 11 January 1985 on the Waldheide near Heilbronn. During this accident, three members of the US Army were killed, nine were injured. The accident investigation was finished by the American investigation committee in December 1985. It confirms the
Damage due to lightning and surges
Figure 2.2.5 a
37
Newspaper reports concerning lightning strikes to planes, the control tower of the Frankfort/Main airport, the Changi airport (Singapore) and the Düsseldorf airport
38
Overvoltage protection of low voltage systems
statement of the first accident report of 15 April 1985, that a discharge of static electricity was the reason for the accident . . .” [The results are then elaborated] From the evidence supplied, the report of 15 April 1985 concludes that a discharge of static electricity caused a spark discharge in the propelling charge of the motor stage, which was the cause for the fire accident.
On 14 November 1964 the space ship Apollo 12 and then the Saturn V rocket were struck by lightning 36 seconds after lift-off from Cape Canaveral. The space ship was about 2 000 m above ground when a lightning strike between the rocket and the launching platform on the ground was noticed. The crew registered disturbances of the energy supply, a number of other electrical disturbances and the response of some safety switches. On 26 March 1987, a 78 million dollar Atlas Centaur rocket went out of control 51 seconds after its launch from Cape Canaveral and had to be destroyed over the Atlantic together with its freight, an 83 million dollar Pentagon satellite. The reason for the loss of control was a lightning strike to the nose of the rocket. A piece of fibreglass from the wreck revealed a carbonized hole, having a diameter of about 5 cm, which was very similar to the holes registered after lightning strikes to airplanes. Owing to the strike, the main computer gave false commands to the driving engines so that the rocket’s trajectory failed and it had to be destroyed. A lightning strike tripped the ignition mechanisms of three small research rockets on 10 June 1987 which were ready for launch at the NASA base on Wallops island, offshore Virginia. On board the rockets were measuring devices for thunderstorm research. The rockets had a common earthing system. According to eyewitness reports, they lifted off ‘simultaneously’ as lightning struck. After a short flight, they fell into the Atlantic without causing any damage. Newpaper reports about lightning strikes to passenger planes and control towers at airports (Figure 2.2.5 a) show that the hazard can extend beyond the immediate system that is damaged.
Sources DOLOMITEN: ‘Blitzeinschläge in Flugzeuge’ No. 230 (2–3 Oct. 1993) SONNTAG AKTUELL, STUTTGART: ‘Ein Blitz zerschlug die Radarnase des Airbus – Passagiere wohlauf’ (3 Oct. 1993) BLITZSCHLAG IN CHANGI AIRPORT/SINGAPUR (summer 1995)
2.2.6 Damage to wind power stations The lightning protection of wind power stations is of current and future importance in Britain, Germany and other European countries. Lightning damage, especially to rotor blades (Figure 2.2.6 a), greatly exceeds
Damage due to lightning and surges
39
what is expected, both in frequency and height. Cases are known where insurance companies see no possibility of further insurance after a single lightning strike, that is, until the operator or the producer provides an adequate lightning protection system (Figure 2.2.6 b).
Figure 2.2.6 a
Lightning damage to the rotor blade of a wind power generator
2.2.7 Catastrophic damage At the 21st International Conference on Lightning Protection (ICLP), S. Lundquist described an especially intense lightning storm in Skane, Southern Sweden, on 1 July 1988. The fire brigade in the town of Lund recorded 1400 alarms. There was a breakdown of the telephone exchange and the mobile police radio was damaged. As an example of many similar life-endangering cases, the situation in the municipal hospital was described. As the 130 kV system failed due to the lightning strike, the hospital was deprived of power for 80 minutes. The lights went out, elevators stopped and the appliances in the intensive care unit could not work. The emergency power generator refused to start because the control computer was damaged; because of the failure of the telephone and the central fire alarm, the technical staff could not be called. When they had managed to start the emergency power generator by hand after half an hour, it failed shortly afterwards due to overheating as the ventilator was supplied by the unfused system. There was serious damage also to the low-voltage mains distribution, the control room and the computer terminals. This episode was particularly horrendous. The consequences of lightning strikes into tall or extended buildings become apparent from events reported from all over the world. Lightning strikes into large-scale buildings, such as office buildings and department stores, cause current failures resulting in: stoppage of full elevators, breakdown of the lighting, tripping of sprinkler systems, flooding of rooms by protective gas, blocking of electronically secured
40
Overvoltage protection of low voltage systems
Figure 2.2.6 b
Report from the Stuttgarter Zeitung, 25 March 1995
doors and garage doors, failure of air-conditioning systems as well as breakdown of the telephone network (Figure 2.2.7 a) and the control systems. Failures of this kind can lead to life-endangering situations and, not least, panic. What characterizes disturbances and failures due to a lightning strike in a building is that safety-relevant systems may be involved at the same time, as well as the infrastructure over a wide area that may also be disturbed. During a thunderstorm with spatial and temporal distribution of lightning, vast damage to vital infrastructure is possible. Catastrophic events, as described by some examples, should not be tolerated. Therefore, precautions must be taken to avoid personal danger. Safety must be
Damage due to lightning and surges
Figure 2.2.7 a
41
Lightning strike causes collapse of the telephone network (Source: Thüringer Allgemeine, 29 June 1994)
guaranteed for the power and information technology systems that are absolutely necessary for vital infrastructure in special situations. These include: airports, public transport, traffic guide and signal systems, hospitals, power stations, above all nuclear power stations and switching plants, high-power transmitters, signal and alarm systems for civil protection, meeting places, schools, kindergardens and mass sports facilities, office and computing centres, buildings with extended safety systems, systems for large-scale supervision of pollutants (including radioactivity) in the air, water and ground, control and alarm systems for defence purposes, telephone exchanges and satellite and relay stations.
Sources LUNDQUIST St.: ‘Effects on the society of an intense lightning storm’, Tagungsband 21. Internationale Blitzschutzkonferenz (ICLP), Berlin (22–25 Sept. 1992) THÜRINGER ALLGEMEINE: ‘Ein Blitz legte Telefone “tot” ’ (29 June 1994) HASSE, P., and WIESINGER, J.: ‘Can you avoid disasters caused by lightning?’ DEHN Publication No. SD 261E, reprint from etz, 1993, 2, pp. 154–156
Chapter 3
Origin and effect of surges
Electromagnetic compatibility (EMC) engineering usually proceeds from an interference model consisting of a source of interference (transmitter), a coupling mechanism (path) and a potentially susceptible equipment (receiver) (Figure 3 a). Electrical systems with electronic devices as potentially susceptible equipment are endangered by conducted interferences and interfering radiation (Figure 3 b) from the following six sources of interference: (i) Direct and close-up lightning discharges Lightning electromagnetic impulse (LEMP): predominantly conducted interference such as lightning currents and partial lightning currents, potential increase of the struck system as well as interfering radiation. (ii) Power technical switching operations Switching electromagnetic impulse (SEMP): predominantly conducted interference as well as magnetic interfering radiation. (iii) Power technical system perturbation Predominantly conducted interference with voltage distortions. (iv) Electrostatic discharges (ESD): predominantly conducted interference by spark discharge. (v) Low and high frequency transmitters Resulting in continuous interfering radiation.
Figure 3 a
Interference model
44
Overvoltage protection of low voltage systems
Figure 3 b
Electronic system endangered by radiation and conducted interference
(vi) Nuclear explosions Nuclear electromagnetic impulse (NEMP): with a resulting impulse-shaped interfering radiation.
The coupling between the source of interference and potentially susceptible equipment can be realized by either conduction and/or radiation (electric field, magnetic field or electromagnetic field). The coupling path can be described in the equivalent circuit diagram by combinations of resistances and/or capacitances and/or inductances. Potentially susceptible equipment includes telecommunications engineering systems (i.e. electrical systems with electronic equipment and facilities). In lightning protection engineering, structural facilities, such as meeting places and areas with fire and explosion hazards, are considered to contain potentially susceptible equipment in the sense of EMC. Such potentially susceptible equipment is found in (i) commercial areas (e.g., industry, trade, commerce, agriculture, banks and insurance buildings), (ii) public areas (e.g., hospitals, meeting places, air traffic control facilities, museums, churches and sports facilities), and (iii) private areas. In the following Sections, lightning discharges and switching operations as sources of interference are described according to their priority.
Sources DIN EN 61000 series. ‘Electromagnetic compatibility (EMC)’.
Origin and effect of surges
45
3.1 Atmospheric overvoltages Lightning, as a source of interference, affects buildings and indoor electrical equipment and systems. Surges of atmospheric origin (Figure 3.1 a) are basically due to either a direct-/close-up strike or a remote strike. In the case of a direct strike (Figure 3.1 a, case 1 ), lightning strikes the protected building; but in the case of a close-up strike, lightning strikes an extended system or a line (e.g., a pipeline, data or power transmission line) leading directly into the protected system. However, in the case of a remote strike (Figure 3.1 a, case 2 ), for example, the overhead line is struck. ‘Reflected surges’ (travelling waves) are produced in transmission lines by cloud-to-cloud lightning, and overvoltages are induced by lightning in the surrounding area.
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3.1.1 Direct and close-up strikes Lightning current in a lightning channel and in the lines of the lightning protection system (a) causes a voltage drop at the impulse earth resistance of the earthing system ( 1a in Figure 3.1 a) and (b) induces surge voltages and currents in loops formed by installation lines inside the structure ( 1b in Figure 3.1 a). Owing to the voltage drop at the impulse earth resistance, partial lightning currents also will be discharged by the supply lines that have been connected as a measure of lightning protection equipotential bonding. A lightning strike in the surrounding area causes induced surge voltages and thus surge currents in installation loops especially due to its magnetic interfering radiation. If lightning strikes a feeding overhead
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Figure 3.1 a
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Reasons for surges at lightning discharges
46
Overvoltage protection of low voltage systems
line, there will be conducted surge voltages and currents on the incoming power line. Lightning between thunderstorm cells in clouds generates conducted surge voltages and currents on power lines and on other wideranging line systems due to interfering electromagnetic radiation. The parameters of lightning current components (first partial lightning surge current, subsequent lightning surge current and lightning long duration current) are specified in the following standards: VG 95 371 in accordance with IEC 61024-1, DIN V ENV 61024-1 (VDE 0185 Part 100), IEC 61312-1 and DIN VDE 0185 Part 103 (Figure 3.1.1 a). Here three protection levels are specified in accordance with IEC, or two degrees of danger in accordance with VG (Table 3.1.1 a). If an exact analysis is not possible or justified because of the expense, the partial lightning currents on supply lines coming from a struck building can be estimated in accordance with IEC 61312-1 and DIN
Figure 3.1.1 a
Table 3.1.1 a
Lightning current components (protection level I acc. to IEC 61024-1/ENV 61024-1 or degree of danger ‘high’ acc. to VG 96901 Lightning current parameters
Origin and effect of surges
47
VDE 0185 Part 103. As shown in Figure 3.1.1 b, it is assumed that 50% of the lightning current flows into the earthing system of the structure and 50% is distributed equally to the outgoing remote-earthed supply systems (e.g., piping, power and communication lines). To make things less complicated one assumes that the partial lightning currents in every supply system will be distributed equally to the different conductors (e.g., L1, L2, L3, and PEN of a power technical cable or four wires of a data line). In DIN V ENV 61024-1 (VDE V 0185 Part 100) annex C there is a method to estimate the lightning partial currents discharged by the incoming lines (for the case when lightning strikes the protected system). Hence, the lightning current will be distributed to the earthing system, the external conductive parts and the incoming lines (which are connected directly or by arresters) now as follows: The share It of lightning current on every external conductive part and every line depends on their number, their equivalent earth resistance and the equivalent earth resistance of the earthing system: It =
Z×I nt × Z + Zt
where Z is the equivalent earth resistance of the earthing system, Zt is the earth resistance of the external conductive parts or lines, nt is the total number of the external conductive parts or lines and I is the lightning current according to the protection level. If electrical or information technology (IT) lines are not shielded or laid in metal conduits, every conductor carries a partial current according to It/n′ where n′ is the total number of conductors in these lines (Table 3.1.1 b).
Figure 3.1.1 b
Estimation of the partial lightning currents on supply systems (acc. to IEC 61312-1; VDE 0185 Part 103)
48
Overvoltage protection of low voltage systems
Table 3.1.1 b
Equivalent earthing resistances Z and Z1 depending on the earth resistivity
Sources VG 95 371-2: ‘Elektromagnetische Verträglichkeit (EMV) einschliesslich Schutz gegen den elektromagnetischen Impuls (EMP) und Blitz’; Allgemeine Grundlagen; Begriffe (Beuth Verlag, GmbH, Berlin), March 1994 IEC 61024-1: ‘Protection of structures against lightning. Part 1: General principles’. International Electrotechnical Commission, Geneva CH-1211, March 1990 DIN V ENV 61024-1 (VDE V 0185 Teil 100): ‘Blitzschutz baulicher Anlagen. Teil 1: Allgemeine Grundsätze’ (VDE Verlag, GmbH, Berlin/Offenbach), Aug. 1996 IEC 61312-1: 1995-02: ‘Protection against lightning electromagnetic impulse. Part 1: General principles’. Central de la Commission Electrotechnique Internationale. Geneva CH-1211, Feb.1995 DIN VDE 0185 Teil 103: ‘Schutz gegen elektromagnetischen Blitzimpuls. Teil 1: Allgemeine Grundsätze’. (IEC 1312-1: 1995, modifiziert,) (VDE Verlag, GmbH, Berlin/Offenbach) Sept. 1997
3.1.1.1 Voltage drop at the impulse earthing resistance The maximum voltage drop ûE arising at the impulse earthing resistance Rst of the affected building is calculated in terms of the maximum value î of lightning current (Figure 3.1.1.1 a): ûE = îRst
This voltage drop ûE, however, is not dangerous for the protected system, if the lightning protection equipotential bonding has been installed effectively. National as well as international lightning protection standards presently call for a comprehensive lightning protection equipoten-
Origin and effect of surges
Figure 3.1.1.1 a
49
Potential increase compared with the distant earth by the peak value of the lightning current
tial bonding, where all lines (incoming or outgoing) are connected directly or by spark gaps or surge protective devices to the earthing system. In the event of a lightning strike, the potential of the whole system will rise by ûE , but, within the system, there will be no dangerous differences. 3.1.1.2 Induced voltages in metal loops The maximum rate of lightning current rise, Δi/Δt, effective during the period Δt, determines the peak values of electromagnetically induced voltages in all open or closed installation loops which are in the vicinity of conductors carrying lightning current. The magnetically induced square-wave voltage, U, in a metal loop during a period of Δt is given by (Figure 3.1.1.2 a): U=M
Δi
冢 Δt 冣
where U is in V, M is the mutual inductance of the loop in H and Δi/Δt the current rate of rise in A/s. For the sizing of lightning protection systems, the maximum values of the average front current rate of rise I/T1, effective during the front time T1 , of Table 3.1.1 a can be used. To estimate what maximum induced square-wave voltages, U, have to be taken into account in installation loops (e.g., in a building) it is assumed that the loops are in the vicinity of infinitely extended, lightning current-carrying down conductors. For the square-wave voltage of a square loop formed by an infinitely wide lightning current-conducting line and an installation line (e.g., the protective conductor of the electrical installation, which is connected to
50
Overvoltage protection of low voltage systems
Figure 3.1.1.2 a
Induced square-wave voltages in loops by the rate of rise Δi/Δt of the lightning current
the down conductor of the lightning protection system at the equipotential bonding bar), the following is applicable: U = M1
Δi
冢Δt 冣
where U is in kV, M1 is the mutual inductance of the loop in μH and Δi/ Δt the current change in the lightning current conducting line in kA/μs. M1 depends on the side length a of the loop and the cross section q of the lightning current conducting line. This can be taken from Figure 3.1.1.2 b. According to the requirements, Δi/Δt = I/T1 can be taken from Table 3.1.1 a (Figure 3.1.1.2 c). For a square loop, formed by an installation line which is insulated from an infinitely wide lightning current conducting line, the following is applicable for the square-wave voltage: U = M2
Δi
冢Δt 冣
where U is in kV, M2 is the mutual inductance of the loop in μH and Δi/ Δt the current change in the lightning current conducting line in kA/μs. M2 depends on the side length of the loop a and the distance s between the loop and the lightning current conducting line. This can be taken from Figure 3.1.1.2 d. Δi/Δt = I/T1 is taken from Table 3.1.1 a, according to the requirements (Figure 3.1.1.2 e). Apart from the induced effects in wide loops, which are due to installation configurations, the induced effects in very small elongated loops formed by parallel wires of unshielded, layer-wise stranded, cables in the surroundings of lightning current conducting lines are also of interest. Induced voltages arising between the wires are called ‘transverse volt-
Origin and effect of surges
51
Figure 3.1.1.2 b
Mutual inductance M1 to calculate the square-wave voltages in square loops, formed by lightning current-carrying conductor and installation line
Figure 3.1.1.2 c
Example
ages’. They can be harmful especially to electronic equipment. For a small elongated loop formed by the wires of an installation line and run in parallel to an infinitely wide lightning current conducting line, the following is applicable for the square-wave voltage: U = M′3 l
Δi
冢Δt 冣
where U is in V, M′3 is the wire length-related mutual inductance of the loop in nH/m, l is the length of the installation line in m and Δi/Δt the current change in the lightning current conducting line in kA/μs. M′3 depends on the distance of the wires b, and on the distance s between the installation line and the lightning current conducting line. This can be
52
Overvoltage protection of low voltage systems
Figure 3.1.1.2 d
Mutual inductance M2 to calculate the square-wave voltages in square loops, formed by installation line (an equipotential bonding line, between the loop and the lightning currentcarrying conductor, does not have any influence on M2).
taken from Figure 3.1.1 2 f. Δi/Δt = I/T1 is to be taken from Table 3.1.1 a, according to the requirements (Figure 3.1.1.2 g). For a small elongated loop, formed by the wires of an installation line and run in a distance vertically to an infinitely wide lightning current conducting line, the square-wave voltage is given by: U = M′4 b
Δi
冢Δt 冣
where U is in V, M′4 is the wire-distance-related mutual inductance of the loop in nH/mm, b is the wire distance in mm and Δi/Δt the current change in the lightning current conducting line in kA/μs. M′4 depends on the line length l and the distance s between the installation line and the lightning current conducting line. This can be taken from Figure 3.1.1. 2 h. Δi/Δt = I/T1 is to be taken from Table 3.1.1 a, according to the requirements (Figure 3.1.1.2 i). In contrast to the high voltage values in the case of wide loops, there are only induced voltages up to about 100 V in small, elongated loops. But, keep in mind that these are transverse voltages on information technology lines, which are operated by nominal voltages in the range 1–10 V and which are connected to surge-sensitive electronic equipment. In the case of lines with twisted wires and especially in the case of electromagnetically shielded lines, the induced square-wave voltages will be very much reduced compared to the values calculated according to the above equations and the transverse voltage values are usually not dangerous.
Origin and effect of surges
53
Figure 3.1.1.2 e
Example
Figure 3.1.1.2 f
Mutual inductance M′3 to calculate the square-wave voltages in two-wire lines (an equipotential bonding line, between the loop and the lightning current-carrying conductor, does not have any influence on M′3).
Figure 3.1.1.2 g
Example
54
Overvoltage protection of low voltage systems
Figure 3.1.1.2 h
Mutual inductance M′4 to calculate the square-wave voltages in two-wire lines (an equipotential bonding line, between the loop and the lightning current-carrying conductor, does not have any influence on M′4).
Figure 3.1.1.2 i
Example
If a metal loop is short-circuited or its insulating distance punctured due to the induced square-wave voltage U, an induced current ii flows in the loop for which the following equation is applicable:
冢 冣
dii 1 M di + ii = dt π L dt
with τ =
L R
where t is the time in s, τ is the time constant of the loop in s, R is the ohmic resistance of the loop in Ω, L is the self-inductance of the loop in
Origin and effect of surges
55
H, M is the mutual inductance of the loop in H and i the lightning current in the lightning current conducting line in A. Formulas and examples to calculate the self-inductance L are indicated in the ‘Handbuch für Blitzschutz und Erdung’. In the vicinity of the lightning channel or the lightning current conducting lines, rapidly changing magnetic fields will arise due to the extreme rate of increase of the lightning current. Surges of up to 100 000 V are generated by these fields within the building in wide ‘induction loops’ formed by the effects of installation lines, such as power and information technology lines, water and gas pipings. Figure 3.1.1.2 j, for example, shows a computer connected to the power and the data system. The data cable is duly connected to the equipotential bonding bar after entering the building; then the cable goes through the data socket outlet into the computer. The power cable is also connected to the equipotential bonding bar by lightning current arresters and supplies the computer through the power socket outlet. As the power and the data cable are independently installed lines, they can form an induction loop including a surface of 100 m2. The open ends of this loop are in the computer; here the surge, magnetically induced into the loop, becomes effective. Not only in the case of direct lightning strikes, but also in the case of strikes in closer proximity, surges of such intensity can be induced into the loop, causing punctures in the equipment or sometimes even fire. The computer must be protected from these lightning surges ‘on the scene’, meaning at the equipment itself or directly at its power and data socket outlets (Section 5.8.2.3).
Figure 3.1.1.2 j
Electronic equipment endangered by induced lightning overvoltages
56
Overvoltage protection of low voltage systems
Sources HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’ (Pflaum Verlag München; VDE Verlag, Berlin; 4th edn, 1993)
3.1.2 Remote strikes In the case of remote strikes, travelling surges either propagate along the lines ( 2a and 2b in Figure 3.1 a), or lightning strikes ( 2c in Figure 3.1 a) in the vicinity of the protected systems, thereby generating electromagnetic fields which affect the system. In particular, damage due to surges of atmospheric origin in the 1990s has shown that electronic installations, up to a distance of about 2 km from the lightning point of strike, are susceptible to induced or conducted surges and surge currents (Section 2.1). This wide area of danger is due to the increasing sensitivity of high-technology equipment to cables extending beyond the building and the growth in the use of sensitive networks. The maximum permissible length of data transmission lines connecting equipment has increased dramatically with advances in technology. For example, the interface V.24/V.28 (which was introduced during the advent of electronic data processing techniques) specifies the electrical characteristics of line drivers permitting a direct bonding up to about 15 m cable length. Today, however, there are line drivers and interfaces available on the market which allow a direct bonding over twisted twin-core cables up to a length of about 1000 m! When lightning partial currents flow in cables they generate longitudinal and transverse voltages (Figure 3.1.2 a).The longitudinal voltage
䊊
Figure 3.1.2 a
䊊
Surges in a cable
䊊
Origin and effect of surges
57
ul generated between the wire and the metal cable shield creates stress on the insulation of the connected device between its input terminals and the earthed enclosure. The transverse voltage uq is established between the wires and this exerts pressure on the input circuit of the connected device. If the lightning partial current î2 is known, the longitudinal voltage ûl can be calculated from the cable coupling resistance Rk (Table 3.1.2 a).
3.1.3 Coupling of surge currents on signal lines The following examples will demonstrate how surge currents can be coupled ohmically, inductively and capacitively onto the signal lines of extended systems. Consider the arrangement with device 1 in building 1 and device 2 in building 2. The devices are interconnected by a signal line. Furthermore, we will assume that both devices are connected to the Table 3.1.2 a
Coupling resistances at lightning currents
58
Overvoltage protection of low voltage systems
respective equipotential bonding bar (PAS) in the buildings by means of protective conductors PE. 3.1.3.1 Ohmic coupling In Figure 3.1.3.1 a lightning strikes building 1, causing a potential difference of some 100 kV at the ohmic earth resistance RA1 . A voltage of this magnitude is sufficient to sparkover the insulation distance in devices 1 and 2 so that an ohmically cross-coupled surge current can flow from PAS 1, through device 1, along the signal line, through device 2, PAS 2 and RA2. The value of this surge current (it can have a peak value of several kA) depends on the relative values of the ohmic resistances RA1 and RA2. 3.1.3.2 Inductive coupling As already shown, voltages are induced in metal loops by the inductive fields of the lightning channel or the lightning current conducting lines. Figure 3.1.3.2 a shows the two wire signal line between devices 1 and 2, forming an induction loop. A transverse voltage of several kV will be induced in this loop if lightning strikes building 1, giving rise to an incoupled current of up to several kA. These voltages and currents stress the components at the inputs or outputs of the equipment. Figure 3.1.3.2 b shows another possible example of inductive coupling. The induction loop is formed by the signal line and the earth. If lightning strikes building 1, a high voltage (some 10 kV) will be induced in this loop leading to a sparkover of insulation distances in devices 1 and 2 and to an incoupled current of several kA.
Figure 3.1.3.1 a
Ohmic coupling
Origin and effect of surges
Figure 3.1.3.2 a
Inductive coupling: Induction loop between the wires of the signal line
Figure 3.1.3.2 b
Inductive coupling: Induction loop between signal line and earth
59
3.1.3.3 Capacitive coupling If lightning strikes the ground or a lightning conductor, the lightning channel or lightning conductor will be raised to a high voltage (some 100 kV) compared to the surroundings because of the potential difference at the earth electrode resistance RA. The signal line between device 1 and device 2 in Figure 3.1.3.3 a is capacitively coupled with such a lightning channel or lightning
60
Overvoltage protection of low voltage systems
Figure 3.1.3.3 a
Capacitive coupling
conductor. The coupling capacities are charged and cause an ‘injected’ current (some 10 A) which flows to the ground over the insulation distances in devices 1 and 2.
3.1.4 Magnitude of atmospheric overvoltages Remote strikes initially cause surges of some 10 kV. The generated currents are relatively low in value. Direct strikes, however, give rise to lightning currents of far greater and more severe magnitude: currents of 200 kA (protection level I) and voltage peaks of several 100 kV can occur. Low-voltage installations can usually only withstand impulse breakdown voltages of several kV and therefore are susceptible to damage, or even destruction, by the tens of kV produced by remote strikes or 100 kV produced by direct strikes (Table 3.1.4 a). The withstand voltage of some electronic devices can be as low as 10 V. Hence, the values of voltages occurring due to atmospheric discharges can be 100 to 10 000 times higher than the voltages that can be carried non-destructively by lowvoltage systems containing electronic equipment. Therefore, these high values of overvoltages must be reduced to values which are clearly below the permitted impulse breakdown/sparkover voltages by means of protective measures or surge protective devices. To guarantee protection, even in the event of direct lightning strikes, the surge protective devices employed must also be able to discharge high partial lightning currents non-destructively.
Origin and effect of surges Table 3.1.4 a
61
Impulse flashover voltages/impulse breakdown voltages (1.2/50 μs) in electrical systems and equipment up to 1000 V
Sources HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’ (Pflaum Verlag, München; VDE Verlag, Berlin; 4th edn, 1993) HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatz elektronischer Geräte auch bei direkten Blitzeinschlägen’, (Verlag TÜV Rheinland, Köln, 3 aktualisierte Auflage 1993) HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept’ (Pflaum Verlag, München; VDE Verlag, Berlin-Offenbach, 1994)
3.2 Switching overvoltages Switching overvoltages in power plants can also affect low-voltage systems and secondary engineering systems, especially due to capacitive coupling. In certain cases, these values can exceed 15 kV. Examples of the cause of these switching overvoltages are as follows: (a) Disconnection of an open-circuit power line (or capacitors) (Figure 3.2 a). When the switch opens, the instantaneous value of the supply voltage on the line results in a high potential difference between the system and the disconnected line. The potential difference, which is established in only a few milliseconds, can cause a flashback between the switch contacts that are yet to close. The line voltage then balances at a level equal to the instantaneous value of the supply
62
Overvoltage protection of low voltage systems
Figure 3.2 a
Switching surges on disconnection of a capacitance
voltage and the arc between the switch contacts is quenched. This process can occur several times. The switching overvoltage generated by the equalization of the appropriate instantaneous value of the supply voltage has the characteristic of a damped oscillation with a frequency of several 100 kHz. The initial amplitude of these switching surges always corresponds to the potential difference between the switch contacts at the moment of the flashback and this amplitude can be a multiple of the nominal supply voltage. (b) Disconnection of an open-circuit transformer. If an open-circuit transformer is disconnected from the network, its self-capacitance is loaded by the energy of the magnetic field. The inductive–capacitve circuit now oscillates until all of the energy in the ohmic resistance of the circuit is converted into heat. The resulting switching overvoltages can reach amplitudes of several times the value of the nominal supply voltage. (c) Earth fault in the floating (earth-free) network. If an earth fault occurs at the outer conductor of a floating network, then the potential of the complete conductor system will be altered by the value of the voltage of the affected conductor with respect to earth. If the earth fault arc interrupts, the effect is similar to that of an opencircuit conductor or capacitor being disconnected: switching overvoltages will develop with damped oscillations. In addition to switching overvoltages from power plants of this nature, which capacitively influence low-voltage systems, rapid variations in current can also generate surges in low-voltage systems by inductive coupling. Such sudden current variations can be due to either the connection or disconnection of a heavy load, or a short circuit, an earth fault or double earth fault. Switching overvoltages can also be generated within the low-voltage systems themselves due to the following: disconnection of inductances connected in parallel with the source • the of voltage, such as transformers, inductors or coils of contactors and
Origin and effect of surges
•
•
•
63
relays. (In this case, switching overvoltages are generated in a similar way to that described above for the disconnection of an open-circuit power transformer.) the disconnection of inductances in the series arm of the current circuit such as conductor loops, series inductors, or the inductances of the actual conductors. (These inductances try to maintain the flow of current, even if the circuit is interrupted. The magnitude of the switching overvoltages that arise depends on the value of the current at the time of disconnection.) intentional disconnection of circuits by means of switches, or unintentional disconnection brought about by the tripping of fuses or circuit breakers, or by line discontinuity before the natural current zero-axis crossing. (Rapid changes in current resulting from occurrences such as these give rise to switching surges, normally with damped oscillations, which are a multiple of the nominal voltage of the system.) by phase control circuits, commutation effects in brush collector systems, and by sudden unloading of machines and transformers.
Extensive measurements taken in different low-voltage networks have shown that the most remarkable surges have been caused by interfering radiation of arcs generated in switchgear. Electromagnetic interference by switching in power technical systems is usually more frequent than lightning interferences. For conducted, broadband interference a difference is made in the EMC standards between high and low energy impulses or pulses depending on the type of switching operation. It is possible that switching interference is generated outside a building and enters through the power lines or it can be generated internally. This is either defined analogously to the lightning interference as combined surge voltage and surge current interference or as impressed surge voltages. In part the broadband, high energy, conducted interference of switching processes is equated to the conducted lightning interference inside the building (with a duly carried out lightning protection equipotential bonding). So interference for different types of environment with correspondingly adjusted peak values is defined in the VG standards (Tables 3.2 a and 3.2 b). An impressed surge voltage due to disconnection processes or overcurrent protective components is defined in DIN VDE 0160. The surge voltage 0.1/1.3 ms (0.1 ms rate of rise, about 0.15 ms front time) with a peak value uN/max will be superimposed on the peak value uN/max of the alternating current voltage. Broadband, low energy switching voltage interference, (i.e. bursts) are shown in DIN VDE 0847 Part 4-4. These impressed voltage impulses 5/50 ns (5 ns rate of rise, about 7.4 ns front time) with peak values
64
Overvoltage protection of low voltage systems
Table 3.2 a
Lightning interference ‘1.2/50 μs’
Table 3.2 b
Lightning interference ‘10/700 μs’
depending on the severity of testing are supplied as pulse packages into power and communication lines through coupling capacities. Apart from conducted interference, considerable interfering radiation can also be due to the switching processes themselves (e.g. arcs generated by the withdrawing of disconnectors) inducing more conducted interferences.
Sources FGH MANNHEIM: ‘Transiente Überspannungen’, Fachberichte der FGH Mannheim, etz-a Elektrotech. Z., 1976, 97(1), pp. 2–27 MENGE, H.-D.: ‘Ergebnisse von Messungen transienter Überspannungen in Freiluft-Schaltanlagen’, etz-a Elektrotech. Z., 1976, 97(1), pp. 15–17
Origin and effect of surges
65
LANG, U., and LINDNER, H.: ‘Überspannungen in Hochspannungsschaltanlagen – Schutz von Sekundäreinrichtungen’, Elektrizitätswirtschaft, 1986, 22, pp. 680–683 SCHWAB, A. J.: ‘Elektromagnetische Verträglichkeit’ (Springer Verlag, Berlin, Heidelberg, New York, 1990) HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatz elektronischer Geräte auch bei direkten Blitzeinschlägen’, 3. aktualisierte Auflage (Verlag TÜV Rheinland, Köln, 1993) HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept’ (Pflaum Verlag, München; VDE Verlag, Berlin-Offenbach, 1994) VDEW: ‘Hinweise für die Messung von transienten Überspannungen in Sekundärleitungen innerhalb von Freiluft-Schaltanlagen’ Vereinigung Deutscher Elektrizitätswerke – VDEW e. V., Ausgabe Oct. 1975 DIN EN 61000-4-5 (VDE 0847 Teil 4-5): 1996-09: ‘Elektromagnetische Verträglichkeit (EMV)’. Teil 4: Prüf- und Messverfahren. Hauptabschnitt 5: Prüfung der Störfestigkeit gegen Stossspannungen (IEC 1000-4-5: 1995); Deutsche Fassung EN 61000-4-5: (VDE Verlag, GmbH, Berlin/Offenbach, 1995) DIN EN 61000-4-4 (VDE 0847 Teil 4-4): 1996-03: ‘Elektromagnetische Verträglichkeit (EMV)’. Teil 4: Prüf- und Messverfahren. Hauptabschnitt 4: Prüfung der Störfestigkeit gegen schnelle transiente elektrische Störgrössen/Burst; EMV-Grundnorm (VDE Verlag, GmbH, Berlin/Offenbach, March 1996) DIN VDE 0160: 1988-05: ‘Ausrüstung von Starkstromanlagen mit elektronischen Betriebsmitteln’ (VDE Verlag, GmbH, Berlin/Offenbach, May 1988) DIN-VDE-Taschenbuch 515: ‘Elektromagnetische Verträglichkeit 1. DINVDE-Normen’ (VDE Verlag, GmbH, Berlin/Offenbach, 1991) VG 96 903 Teil 76/08.89: ‘Schutz gegen Nuklear-Elektromagnetischen Impuls (NEMP) und Blitzschlag’. Prüfverfahren, Prüfeinrichtungen und Grenzwerte. Verfahren LF 76: Prüfung mit Direkteinspeisung eines Spannungsimpulses 1,2/50 s und eines Stromimpulses 8/20 s (Beuth-Verlag, GmbH, Berlin, Aug. 1989)
Chapter 4
Protective measures, standards
For a considerable time increasingly refined methods have been used worldwide to measure lightning currents at high towers, HV overhead lines and in lightning trigger stations. Field measuring stations also register the radiated electromagnetic interference fields of lightning discharges. From the results of research, lightning as a source of interference is understood and defined with regard to the present protection problems. It is also possible to simulate lightning currents with their extreme values in the laboratory; this is a prerequisite for testing protective installations, components and devices. Also lightning interference fields can be simulated for the testing of information technology equipment. Because of such wide ranging basic research and the development of protection concepts, such as the concept of lightning protection zones as organizing principle of an EMC, as well as suitable protective measures and devices against field generated and conducted interference due to lightning discharges, we now have the necessary conditions for protecting systems in such a way that the final risk of failure can be kept extremely low. Thus, it can be guaranteed that the essential infrastructure can be maintained and catastrophes avoided in cases of extraordinary atmospheric threats. The necessity of standardizing complex EMC-oriented lightning protection measures, containing also so-called surge protection measures, has been realized. The International Electrotechnical Commission (IEC) as well as the European (Cenelec) and national standards committees (DIN VDE, VG) produce standards on the following: interference of lightning discharge and its statistical • Electromagnetic distribution as a basis for the assignment of interferences to protection
• • •
levels Methods to estimate the risk of determining the protection levels Measures to discharge the lightning current Measures for screening electromagnetic lightning fields
68
Overvoltage protection of low voltage systems
to discharge conducted lightning interference • Measures Requirements and tests for protective components • Protective concepts within the scope of an EMC-oriented manage• ment plan When designing a protection system, it is first necessary to decide whether to protect the device or installation solely against destruction or against interference as well. The effects of interference are normally covered by ‘classical’ considerations of the electromagnetic compatibility (EMC) of a device; and the possible destruction of devices is the most important consideration in surge protection analysis. In contrast to normal electromagnetic interference, lightning discharges and nuclear explosions are relatively rare and of very short duration. Hence, system design is usually limited to avoiding the destruction of devices by surges. Short-term signal fluctuations can be accepted. This, for example, is the procedure in standard low-voltage systems in wide ranges of industrial measurement and control installations and in telecommunication and electronic data processing systems. In certain special cases, however, such as the control systems of nuclear power stations, alarm systems and military installations, there must be no error signals even in the case of a lightning discharge or nuclear explosion. Some installations require a combination of lightning protection, switching surge protection, electrostatic discharge protection and protection against nuclear electromagnetic pulses. The protective measures described in the following paragraphs, such as external and internal lightning protection, shielding, and surge limitation, are methods which partly overlap and also complement one another. If possible, they should be considered at the initial stages of construction of structural systems and electrical consumer installations, but sometimes they can be realized subsequently. On passing of the law on the electromagnetic compatibility of devices (‘Guidelines on the application of Council Directive 89/336/EEC of 3 May 1989 on the approximation of the laws of the Member States relating to electromagnetic compatibility’), the ‘equipment’ must have a sufficient immunity also against lightning interference. The word ‘equipment’ does not only mean all electric and electronic devices but also installations and systems which contain electric or electronic modules. To secure, for example, the protection of complex power and information systems of a building in the case of a direct or close-up lightning strike, extensive analysis by a lightning protection expert is necessary. With an EMC analysis, convenient planning for a building and reliable cooperation of all electronic building functions at normal operation can be secured. With priority system planning, the EMC measures of lightning protection are realized so that safe, interference-free operation is possible; likewise for the case of direct lightning interference.
Protective measures, standards 69
Sources HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatz elektronischer Geräte auch bei direkten Blitzeinschlägen’ (Verlag TÜV Rheinland, Köln, 3. aktualisierte Auflage, 1993) HASSE, P.: ‘Blitz-/Überspannungsschutz – Stand der Normung’, 5. Forum für Versicherer (Dehn und Söhne, Nürnberg, Oct.1994) HASSE, P., and WIESINGER, J.: ‘Lightning protection for fulfilling the principles of EMC ’, DEHN publication No. SD 321E, reprint from etz, 7, 1995, pp.12–13 HASSE, P.: ‘Blitzschutz für Gebäude und Elektrische Anlagen – 1’, VDE/ABBBlitzschutztagung, 1996, 11, pp. 960–964; 1996, 12, pp. 1107–1112
4.1 Lightning protection According to national and international lightning protection engineering and standards, a lightning protection system for buildings requires the protection of the whole system against the effects of lightning. This consists of external lightning protection and internal lightning protection. External lightning protection involves the air termination systems, the down conductors and the earthing system. Internal lightning protection involves all additional measures preventing magnetic and electric implications of lightning current in the volume to be protected. Above all else, there is lightning protection equipotential bonding which reduces the potential differences caused by lightning current. According to the international lightning protection standard, the ‘protected volume’ is the structural system that is to be protected by a lightning protection system. The primary task of lightning protection is to intercept lightning by an air termination system, to discharge the lightning current through a down conductor system to the earthing system where it will be dissipated into the ground. Furthermore, the ohmically, capacitively and inductively ‘incoupled’ interference must be reduced to harmless values in the protected volume. In Germany, DIN VDE 0185 Parts 1 and 2 have been enacted since 1982 for the erection, planning, extension and alteration of lightning protection systems. This VDE guide, however, does not include details of whether a lightning protection system has to be provided for a building or not. Building regulations of the German Federal Countries, national and regional regulations and specifications, instructions and directions of the insurance companies and the danger characteristics for lightning protection systems in the immovables of the German Federal Armed Forces can be used as decision makers. If a lightning protection system for a structural system or building is not made a prerequisiste by the building regulations of an individual country, it is entirely up to the building supervisory board, the owner or the operator to decide upon its necessity. Should there be a decision for
70
Overvoltage protection of low voltage systems
the installation of a lightning protection system, it must be carried out in accordance with the corresponding standards or relevant regulations. As an accepted rule of engineering, however, a standard or regulation only stipulates the minimum requirements at the time of coming into force. Developments in the field of engineering and related latest scientific findings may be registered from time to time into a new standard or regulation. Thus, the presently valid DIN VDE 0185 Part 1 and 2 only reflects the state of engineering of about twenty years ago. In the interim years there have been important changes in building services management systems and electronic data processing. Thus, a building lightning protection system planned and installed according to the state of engineering twenty years ago will no longer be sufficient. Damage statistics of the insurance companies clearly confirm this fact (Figures 2.1 a and 2.1 b). However, the latest results of lightning research and engineering are reflected in the internationally agreed lightning protection standards. Technical Committee 81 (TC81) of the IEC has international competence, Technical Committee 81X (TC81X) of the Cenelec has European (regional) competence and Committee K251 of the German Electrotechnical Commission (DKE) has national competence in lightning protection standardization. Table 4.1 a shows the current state as well as the future tasks of the IEC standardizing work in this field. Through Cenelec, IEC standards are transferred into European Standards (ES) (sometimes modified): for example, IEC 61024-1 in ENV 61024-1. But Cenelec also works out its own standards: for example, EN 50164-1 to 4 (Table 4.1 b). Figure 4.1 a illustrates the mechanism for the development of an IEC standard through Cenelec to the DKE using the example of IEC 61024-1:
Figure 4.1 a
Lightning protection standards: International (IEC), regional (CLC), national (DKE)
Table 4.1 a
Standards within IEC TC 81
72
Overvoltage protection of low voltage systems
Table 4.1 b
Cenelec-standards ‘Lightning Protection’
61024-1: 1990-03 ‘Protection of structures against lightning. • IEC Part 1: General principles’ has been valid worldwide since March
• •
• •
1990. The European draft standard ENV 61024-1: 1995-01 ‘Protection of structures against lightning. Part 1: General principles’ has been in force since January 1995. This draft standard (translated into the national languages) will be tested in the European countries (for about three years); in Germany, for example, as DIN V ENV 61024-1 (VDE V 0185 Part 100) ‘Gebäudeblitzschutz. Teil 1: Allgemeine Grundsätze’ (with national annex). (‘Lightning protection of buildings. Part 1: General principles’) After final consideration at Cenelec, there will then be the binding standard EN 61024-1 for all European countries. In Germany this standard will be published as DIN EN 61024-1 (VDE 0185 Part 100).
In August 1996 the German draft standard DIN V ENV 61024-1 (VDE V 0185 Part 100) was published (Figure 4.1 b). During the transitional period until the final standard, either this draft standard or the standard DIN VDE 0185-1 (VDE 0185 Part 1): 1982-11 ‘Blitzschutzanlage, Allgemeines für das Errichten’ can be applied. ENV 61024-1 is based on the latest technical state. Its application guarantees safe protection of the structure. Therefore, application of ENV 61024-1, including the national annex, is recommended in order to obtain a more effective protection, on the one hand, and to gather experience in the application of the later exclusively valid European Standard, on the other hand.
Protective measures, standards 73
Figure 4.1 b
Use of the European Draft Standard (ENV) in Germany
Lightning protection measures for special systems DIN VDE 0185-2 (VDE 0185 Part 2): 1982-11 will be treated in a later standard. Until then the standard DIN VDE 0185-2 (VDE 0185 Part 2): 1982-11 is valid. These special systems can be carried out according to ENV 61024-1; additional requirements in DIN VDE 0185-2 (VDE 0185 Part 2): 198211 must be taken into account. A lightning protection system planned and installed according to the draft standard ENV 61024-1 will rather prevent damage at the structure. Persons are protected inside the structure, and they will not be endangered by damage to the structure (e.g., fire). The protection of extended electrical power and information engineering installations in and at the structure cannot be guaranteed by the very measures of lightning protection equipotential bonding according to ENV 61024-1. In particular the protection of information technology equipment (communications technology, instrumentation and control, computer networks etc.) requires special protective measures on the basis of IEC 61312-1: 1995-02 ‘Protection against lightning electromagnetic impulse. Part 1: General principles’ because of the low admissible voltages. The standard DIN VDE 0185-103 (VDE 0185 Part 103), with the regulations of IEC 61312-1, has been valid since September 1997 (Figure 4.1 c). To estimate the damage risk due to a lightning strike, standard IEC 61662: 1995-04 ‘Assessment of the risk of damage due to lightning’ with Amendment 1: 1996-05 ‘Assessment of the risk of damage due to lightning’, Annex C ‘Structures containing electronic systems’ is applicable.
74
Overvoltage protection of low voltage systems
Figure 4.1 c
New German Lightning Protection Standards
Sources DIN VDE 0185: ‘Blitzschutzanlage. Teil 1: Allgemeines für das Errichten. Teil 2: Errichten besonderer Anlagen’ (VDE Verlag, GmbH, Berlin/Offenbach, Nov. 1982) IEC 61024-1: ‘Protection of structures against lightning. Part 1: General principles’. International Electrotechnical Commission, Genève, March 1980 DIN V ENV 61024-1(VDE V 0185 Teil 100): ‘Blitzschutz baulicher Anlagen. Teil 1: Allgemeine Grundsätze’ (VDE Verlag, GmbH, Berlin/Offenbach, Aug. 1996) E DIN EN 50164-1(VDE 0185 Teil 201): ‘Blitzschutzbauteile. Teil 1: Anforderungen für Verbindungsbauteile’. Deutsche Fassung prEN 50164-1: (VDE Verlag, GmbH, Berlin/Offenbach, May 1997) IEC 61312-1: ‘Protection against lightning electromagnetic impulse. Part 1: General principles’. Centre de la Commission Electrotechnique Internationale Genève, Feb. 1995 DIN VDE 0185-103 (VDE 0185 Teil 103): ‘Schutz gegen elektromagnetischen Blitzimpuls. Teil 1: Allgemeine Grundsätze’, (IEC 1312-1: 1995, modifiziert) (VDE Verlag, GmbH, Berlin/Offenbach, Sept. 1997) IEC 61662: ‘Assessment of the risk of damage due to lightning’. Bureau Central de la Commission Electrotechnique Internationale, Genève, April 1995 Amendment 1: ‘Assessment of the risk of damage due to lightning, Annex C: Structures containing electronic systems’. Bureau Central de la Commission Electrotechnique Internationale, Genève, May 1996
4.1.1 Risk analysis, protection levels Basically new in these lightning protection standards are methods for the assessment of the risk of damage due to lightning and the subdivision of the protective measures into protection levels.
Protective measures, standards 75
The assessment of the risk of damage due to a lightning strike into a structure helps the lightning protection planner to decide whether or not a lightning protection system is to be recommended and to choose suitable protective measures. The purpose of choosing a sufficient protection level is to reduce the risk of damage due to direct lightning strikes to below an acceptable value. The selection of a sufficient protection level for the lightning protection system can be based on the expected number of direct strikes (Nd) and on the accepted number of strikes (Nc) that will cause damage. The flow diagram for the selection of the lightning protection systems, is shown in DIN V ENV 61024-1 (VDE V 0185 Part 100) in Figure 4.1.1a.
Figure 4.1.1 a
Flow diagram for the selection of a lightning protection system
76
Overvoltage protection of low voltage systems
Proceeding from a lightning density Ng (lightning strikes per km2 and year), which is applicable for the region where the building stands, the average annual number Nd of lightning strikes to be expected for the building/surface Ae can be determined by means of the equivalent surface Ae (in km2). That is Nd = Ng Ae
The equivalent surface Ae will be determined according to Figure 4.1.1 b. The equivalent surface Ae takes into account that lightning strikes in the direct vicinity of a structure have the same consequence as direct strikes. According to the national annex NB of this standard the following is specified: Nc = A B C
where Nc is the accepted strike frequency, A is the building construction component (type of construction, material), B is the component dealing with the use and contents of the building, and C is the component considering consequential damage. To determine these components, the following are taken into account: A (building construction): construction of the walls, roof • Component construction, roof covering, and roof superstructures. B (building utilization and contents): utilization by • Component people, nature of building contents, value of building contents, and measures and installations for damage reduction.
Figure 4.1.1 b
Determination of the equivalent collection area Ae for an individual building
Protective measures, standards 77
C (consequential damage): danger to the environment • Component due to the building contents, failure of important public services supplied by the building installations, and other consequential damage. The value of the accepted strike frequency Nc must be compared with the actual number of annual strikes Nd. The comparison allows a decision—whether a lightning protection system is necessary or not, and, in the affirmative, what version has to be chosen: If Nd < Nc , a lightning protection system is not necessary. If Nd > Nc, a lightning protection system with efficiency E≥1−
Nc Nd
in accordance with the protection level of Table 4.1.1 a should be installed. After calculation of E, the protection level must be derived from the following: E > 0.98 protection level I with additional protective measures 0.95 < E ≤ 0.98 protection level I 0.90 < E ≤ 0.95 protection level II 0.80 < E ≤ 0.90 protection level III 0 < E ≤ 0.80 protection level IV E < 0 lightning protection not necessary. Additional protective measures, for example, include those to reduce the contact and step voltages, those to avoid the spreading of fire, and those to reduce voltages in sensitive installations induced by lightning. By the protection level the following is stipulated: of the lightning protection system (Table 4.1.1a) • efficacy radius of rolling sphere, protective angle, mesh size (Table 4.1.1 b) • lightning the characteristics (Table 4.1.1 c) • Table 4.1.1 a
Relation between protection level and efficiency
78
Overvoltage protection of low voltage systems
Table 4.1.1 b
Assignment of angle of protection, rolling sphere radius and mesh size to the protection levels
Table 4.1.1 c
Assignment of the lightning current parameters to the protection levels
k to determine the safety distance between the lightning pro• factor tection system and metal installations/electrical and information i
• • •
technology equipment clearances between the down conductors minimum lengths of the earth electrodes inspection intervals.
4.1.2 External and internal lightning protection, DIN VDE 0185 Part 1, DIN V ENV 61024-1 (VDE V 0185 Part 100) DIN V ENV 61024-1 (VDE V 0185 Part 100) as well as DIN VDE 0185 Part 1 essentially deal with (Figure 4.1.2 a): air termination system, down conductor system, earthing system, lightning protection equipotential bonding, and safety clearances (at proximity points).
Protective measures, standards 79
Figure 4.1.2 a
External and Internal Lightning Protection according to IEC 61024-1/ENV 61024-1
The lightning protection system consists of both external and internal lightning protection. External lightning protection consists of the air termination system, the down conductor system and the earthing system. Internal lightning protection includes all additional measures to avoid electromagnetic interference due to lightning current in the protected volume. Lightning protection equipotential bonding is that part of the internal lightning protection which reduces the potential differences caused by lightning current. Lightning protection equipotential bonding is realized by bonding the conductors of the external lightning protection system with the metal frame of the structure, with the metal installations, with the external conductive parts, and with the power and information technology equipment in the volume to protect. Bonding measures include: equipotential bonding lines, if the continuous electric conductivity is not achieved by the natural connections; and arresters, if direct connections with the equipotential bonding lines are not allowed (Figure 4.1.2 b). Lightning protection equipotential bonding must be carried out in accordance with DIN V ENV 61024-1.
4.1.3 Concept of lightning protection zones, DIN VDE 0185-103 (VDE 0185 Part 103) Since September 1997 the international standard IEC 61312-1 ‘Protection against lightning electromagnetic impulse – Part 1: General principles’ is also valid in Germany as DIN VDE 0185-103 (VDE 0185
80
Overvoltage protection of low voltage systems
Figure 4.1.2 b
Lightning protection equipotential bonding for incoming services
Part 103): 1997-09 ‘Schutz gegen elektromagnetischen Blitzimpuls. Teil 1: Allgemeine Grundsätze’. This standard became necessary because of the increasing use of many kinds of electronic systems including computers, telecommunication facilities, control systems etc. (called information systems in this standard). Such systems are used in many fields of commerce and industry, including the control of production facilities with high capital value, wide dimensions and great complexity, where failures due to lightning strikes are very undesirable for cost and safety reasons. A risk analysis which focuses on the LEMP hazard to electronic equipment is indicated in IEC 61662, Amendment 1 ‘Assessment of the risk of damage due to lightning’, Annex C ‘Structures containing electronic systems’. With regard to general principles of protection against lightning strikes DIN V ENV 61024-1 (VDE V 0185 Part 100) is applicable; however, it does not treat the protection of electric and electronic systems. The standard DIN VDE 0185-103 (VDE 0185 Part 103) is concerned with the lightning electromagnetic impulse and its interfering fields and therefore is a basis for the protective system. The general principles for protection against the electromagnetic lightning pulse (or LEMP: lightning electromagnetic impulse) are described in DIN VDE 0185-103 (VDE 0185 Part 103). Here it is shown how a structure can be subdivided into several lightning protection zones (in DIN VDE 0185-103 (VDE 0185 Part 103) called LPZ: lightning protection zone) according to the concept of lightning protection zones, and how the equipotential bonding has to be carried out at the zone interfaces (Figure 4.1.3 a). The protected volume (or ‘volume to protect’) will be subdivided into lightning protection zones. The different protection zones are formed by
Protective measures, standards 81
Figure 4.1.3 a
Example for the subdivision of a building into several lightning protection zones (LPZ) and sufficient equipotential bonding
building screens, shielded rooms and devices using existing metal structures. The individual protection zones are characterized by obvious changes of the fieldborne and conducted lightning interference at their boundaries. When a metal supply system passes a zone boundary and thus the electromagnetic screen of a zone, this supplying system must be treated at the interface. For passive conductors (pipes, cable sheaths) this is done by conductive connections to the zone screen; for electrical lines by the use of arresters that discharge the interfering energy.
82
Overvoltage protection of low voltage systems
In the standard DIN VDE 0185-103 (VDE 0185 Part 103): execution of the protective measures on the basis of the concept • the of lightning protection zones is shown from concept planning to its
• • • • • •
acceptance primary lightning interferences are specified generator circuits are indicated for the simulation of lightning currents the timing functions of the lightning current components are shown for calculation analyses measures of lightning protection equipotential bonding are treated electromagnetic building and room screening is described the application of arresters is determined.
The LEMP-protection management for new buildings, as well as for far-reaching alterations in the execution or use of structures, is described in this standard (Table 4.1.3 a). In the following sections the tasks that must be fulfilled by the different management steps are described and practical examples are given. Table 4.1.3 a
LEMP-protection management for new buildings and for comprehensive alterations in development or utilization of existing buildings
Sources HASSE, P., and WIESINGER, J.: ‘EMV-Blitz-Schutzzonen-Konzept’ (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach, 1994) HASSE, P.: ‘Blitzschutz-Management – Planung und Organisation’. Tagungsband 1. VDE/ABB–Blitzschutztagung ‘Blitzschutz für Gebäude und Elektrische Anlagen’. (Kassel, 29 Feb.–1 March,1996)
Protective measures, standards 83 HASSE, P.: Neu: DIN VDE 0185 Teil 103: ‘Schutz gegen elektromagnetischen Blitzimpuls’. Teil 1: Allgemeine Grundsätze – Anwendung in der Praxis – (I). de (der elektromeister + deutsches elektrohandwerk), 1997, 14, pp. 1352– 1356, 17, pp. 1552–1558, 18, pp. 1691–1693 IEC 61662, Amendment 1: ‘Assessment of the risk of damage due to lightning, Annex C: Structures containing electronic systems’. Bureau Central de la Commission Electrotechnique Internationale, Genève, May 1996
4.1.3.1 LEMP-protection planning The LEMP-protection planning for the system to protect must be carried out by a lightning protection expert (who has well-founded knowledge of EMC) in close coordination with the owner, the architect, the installer of the information system, the planners, and other relevant institutions and, if necessary, with the subcontractors. The planning should begin with definition of the lightning protection levels. 4.1.3.1.1 Definition of lightning protection levels By analysing the risk in accordance with DIN V ENV 61024-1 (VDE V 0185 Part 100), annex F, or according to DIN IEC 61662 (VDE 0185 Part 101), where the structure’s site, the building construction, its use, content, and possible subsequent damage are considered, the adequate protection level for the structure to protect can be determined as described in Section 4.1.1. 4.1.3.1.2 Definition of lightning protection zones As shown in Figure 4.1.3 a, the volume to protect will be divided into protection zones. The different protection zones will be created by the screening of the building, the rooms, and the equipment by using the existing metal components such as metal facades, reinforcements and metallic enclosures. Numbering of the protection zones is according to their damping of the electromagnetic lightning fields. The undamped environs will be defined as lightning protection zone 0 which will be subdivided into the following: protection zone 0 , where direct lightning strikes occur • lightning lightning protection zone 0 , where direct strikes are prevented by the • air-termination system (in accordance with the effectivity of the lightA
B
ning protection level). The definition of lightning protection zones and the determination of their boundaries in the case of complex systems usually will be developed step-by-step, while the lightning protection expert regularly consults the main involved and responsible parties concerning construction and operation, in order to reach an optimally balanced overall concept by using all structural (technical and economical) realities. At this point, it should be emphasized that on defining the protection levels and on determination of the lightning protection zones the
84
Overvoltage protection of low voltage systems
essential basic data for the total costs of the lightning protection system to be planned and installed are fixed. So it is, for example, quite usual to attribute different protection levels to the individual buildings of an extended industrial plant (as shown in Figure 4.1.3.1.2 a) by means of a risk analysis. Depending on the actual requirements, the air terminations, down conductors and earthing systems can be executed as ‘isolated’, ‘partly isolated’, or ‘building integrated’, as shown in Figure 4.1.3.1.2 b. Figures 4.1.3.1.2 c to e show the execution in practice. Best positioning of the air terminations is made possible by means of the rolling sphere method: either in a drawing (Figure 4.1.3.1.2 f a) or using a scale model (Figure 4.1.3.1.2 f b). Only those parts of the building that are touched by the rolling sphere (Figure 4.1.3.1.2 f c), need air terminations. In the following planning step, room shielding measures will be specified. 4.1.3.1.3 Room shielding measures Of special importance for the planning of building and room shields for the lightning protection zones are the existing metal components of the building (e.g., metal roofs and facades, steel reinforcements in concrete, expanded metals in walls, metal lattices, metal supporting structures, metal piping) forming an effective electromagnetic shield, if there is an intermeshed connection. Already by this stage of planning it must be specified (and agreed upon by the construction companies) that: steel reinforcements in ceilings, walls, and floors must be inter• all connected and bonded with the earthing system (at least every 5 m) (Figures 4.1.3.1.3 a)
Figure 4.1.3.1.2 a
Lightning protection zones (LPZ) with protection levels (PL)
Protective measures, standards 85
Figure 4.1.3.1.2 b
(a) Lightning protection zones in case of an ‘isolated’ lightning protection system
Figure 4.1.3.1.2 b
(b) Lightning protection zones in case of a ‘partly isolated’ lightning protection system
Figure 4.1.3.1.2 b
(c) Lightning protection zones in case of a ‘buildingintegrated’ lightning protection system
86
Overvoltage protection of low voltage systems
Figure 4.1.3.1.2 c
Example of an ‘isolated’ lightning protection system
Figure 4.1.3.1.2 d Example of a ‘partly isolated’ lightning protection system
Figure 4.1.3.1.2 e Example of a ‘building-integrated’ lightning protection system
Protective measures, standards 87
Figure 4.1.3.1.2 f
(a) Planning by drawing
Figure 4.1.3.1.2 f
(b) Using a model
Figure 4.1.3.1.2 f
(a–c) Positioning of an air-termination system by means of the rolling sphere method
Figure 4.1.3.1.2 f (c) Surfaces marked are touched by the rolling sphere
88
Overvoltage protection of low voltage systems
Figure 4.1.3.1.3 a
(a)
Figure 4.1.3.1.3 a
(b)
Figure 4.1.3.1.3 a
(c)
Protective measures, standards 89
Figure 4.1.3.1.3 a
(d)
Figure 4.1.3.1.3 a
(e)
Figure 4.1.3.1.3 a
Effective electromagnetic shielding by: (a, b) Steel mats on the roof; (c, d) Bonding of reinforcements in floors, walls and ceilings; (e, f ) Application of fixed earthing terminals for bridging of expansion joints or bonding of reinforcements of prefabricated concrete parts
Figure 4.1.3.1.3 a
(f)
90
Overvoltage protection of low voltage systems
facades will be turned into shields by connecting them with the • metal earthing system (every 5 m or less) (Figure 4.1.3.1.3 a g) sheet metal forms in floors, ceilings, and walls must be intercon• lost nected and bonded with the earthing system (at least every 5 m) constructions must be connected to the earthing system • steel steel reinforcements of the foundations must be connected to the • earthing system (at least every 5 m) (Figure 4.1.3.1.3. a h). 4.1.3.1.4 Equipotential bonding networks Provision must be made, even at the planning phase, that all metal installations entering a lightning protection zone must be connected. This connection must be either directly, or over disconnection spark gaps, or over arresters, to the lightning protection equipotential bonding bar. Such installations include: electrodes (telecommunication earth electrodes, earth electrodes • earth in accordance with DIN VDE 0141 (directly or over disconnection
•
spark gaps), auxiliary earth electrodes, measuring earth electrodes (over disconnection spark gaps), and earth-contact shielding conductors). electric lines (metal sheaths and armour of cables as well as shields of lines, communications cables (telecommunication and data cables), aerial cables, and power cables (under consideration of DIN VDE 0100 Parts 410 and 540)).
Figure 4.1.3.1.3 a
(g)
Protective measures, standards 91
Figure 4.1.3.1.3 a
(h)
Figure 4.1.3.1.3 a
(g–h) Bonding of the continuous interconnected metal façade with the earthing system; (h) Internal surface earth electrode realized by floor slab reinforcement, which is bonded by hot-galvanized steel strips (in raster 5 m x 5 m)
Figure 4.1.3.1.4 a
Lightning protection equipotential bonding bar
lines (water pipes, heating pipes, gas pipes, ventilation and • non-electric air-conditioning ducts, fire extinguishing pipes, and piping of cathodically protected systems or such with stray current protection measures (over disconnection spark gaps)).
92
Overvoltage protection of low voltage systems
In the case of extended technical communication systems, the equipotential bonding bar for the lightning protection must be planned in such a way (approximately at ground level inside the building) that it can take over the function of the ‘earth bus’. Then it usually will be laid as an ‘earth ring bus’ inside the building (Figure 4.1.3.1.4 a). It is required that this ring-equipotential bonding bar be connected to have a low impedance with the earthing system and the zone screen. In the case of protection measures using the concept of lightning protection zones, the planner is free to decide between a mesh-like or star-type configuration of the equipotential bonding system. Usually a mesh-like functional equipotential bonding system (Figure 4.1.3.1.4 b) will be planned. The devices in a protection zone shall be interconnected by lines (as many as possible and as short as possible), with the metal parts of the protection zone and the protection zone screen. Also here the planner will employ the already existing metal components of a building, such as the reinforcement in the floor, the walls and the ceiling, the metal grates in double bottoms and (non-electric) metal installations, such as ventilation pipes and cable racks. Typically, a meshing of at least one metre mesh size will be desired. Figure 4.1.3.1.4 c shows the bonding of two meshed protection zones, whereby the shields are integrated into the equipotential bonding system. Figure 4.1.3.1.4 d illustrates that rather complex zone structures may be planned. Protection zones nested within each other and local protection zones of different equipotential bonding concepts are interconnected here. 4.1.3.1.5 Equipotential bonding measures for supply lines and electric lines at the boundaries of the lightning protection zones As soon as the lightning protection zones for the system to protect have been determined in agreement with all parties concerned, the interfaces for all metal supply systems including the electric lines must then be clearly defined. Wherever a supply system penetrates a zone boundary and, thus, the electromagnetic screen of a zone, this supply system must be treated. For supply systems and lines that do not conduct voltages and currents, this is realized by an electrically conductive connection; live lines will be equipped with arresters that discharge the interfering energies in the case of lightning-induced overvoltages from the lines to the earthed zone screen. Figure 4.1.3.1.5 a, for example, shows the interfaces of supply systems which come from lightning protection zone 0A into lightning protection zone 1 on ground level, and overhead lines coming from lightning protection zone 0A or 0B into lightning protection zone 1. It is the same with all supply systems inside the protected volume: if they lead from one lightning protection zone into another, they must also be treated at the interfaces. In the case of a lightning strike, the lightning current will not only be
Protective measures, standards 93
Figure 4.1.3.1.4 b
Meshed functional equipotential bonding system in a lightning protection zone
Figure 4.1.3.1.4 c
Bonding of lightning protection zones with the correspondingly meshed functional equipotential bonding
Figure 4.1.3.1.4 d
Bonding of lightning protection zones with meshed and starshaped functional equipotential bonding at a complex zone structure
94
Overvoltage protection of low voltage systems
Figure 4.1.3.1.5 a
Interfaces at lightning protection zone boundaries
discharged over the earthing system, but a rather considerable part also over the supply systems entering the lightning protection zone 1 from outside ground. At their points of entry, these systems are bonded with the screen of lightning protection zone 1. If the planner does not make any detailed calculations, it may be assumed, in accordance with DIN VDE 0185-103 (VDE 0185 Part 103), that 50% of the whole lightning current (with its parameters in Table 4.1.1 c defined according to the protection level) must be discharged over the outgoing supply systems. It may be further assumed that the lightning current will be distributed equally to all metal and also electric line systems (Figure 4.1.3.1.5 b). When a line system consists of several component conductors, for example (e.g., outer conductor and protective conductor, a power technical line or several cores of an information technology line) it may be assumed that again the lightning partial current will be distributed equally to the different conductors/ cores of a line system. In the worst case, shields are counted as component conductors. For a closed outer cable shield and copper braid shield, a considerably higher share can flow over the shield than over the inner conductors. Here the current distribution (particularly that depending on the coupling resistance) must be determined individually. It is also possible, in a close-up lightning strike as shown in Figure 4.1.3.1.5 c, that a considerably higher lightning current can be led to the interface at lightning protection zone 1 by one single supply system than would have been the case, according to the above estimation, for a direct strike. This must also be taken into account when the determinations for planning of the equipotential bonding measures are made. 4.1.3.1.6 Cable routing and shielding Two local, spatially separated lightning protection zones can be turned into one lightning protection zone
Protective measures, standards 95
Figure 4.1.3.1.5 b
Partial lightning current on external supplying systems in case of a direct strike into the lightning protection system
Figure 4.1.3.1.5 c
Partial lightning current on external supplying systems in case of a close-up strike
by means of a bonding line screen (a metal cable conduit, a shielded cable route or outer cable shields) (Figure 4.1.3.1.6 a). Easy handling calculation principles for the planner are given in the ‘Handbuch für Blitzschutz und Erdung’ (Handbook for Lightning Protection and Earthing). Figures 4.1.3.1.6 b (a and b) show cable ducts, the reinforcement of
96
Overvoltage protection of low voltage systems
Figure 4.1.3.1.6 a
Line shield bonded with building-shields
Figure 4.1.3.1.6 b
(a) Basic structure
Figure 4.1.3.1.6 b
(b) Practical realization
Figure 4.1.3.1.6 b
Cable duct with continuously interconnected reinforcement
Protective measures, standards 97
which is bonded to a screen. The welded duct reinforcement, with a mesh size of typically 15 cm and a rod diameter of typically 6 mm, which is continuously connected in the longitudinal direction by means of clamps, can be connected directly to the building foundation reinforcement. Within lightning protection zones 1 and higher, electromagnetically shielded cables shall be used for information technology purposes. At least both ends of the shields must be bonded. Then, the shields will also be effective within the scope of the meshed functional equipotential bonding as equipotential bonding lines. Alternatives to shielded cables can be either metal, closed, and continuous cable stages, or metal pipes, or shielded cable conduits. Figure 4.1.3.1.6 c shows how, by parallel routing of power and information technology lines, the surface of the induction line loop can be reduced. As an additional measure the lines can be laid in line shields (e.g., conduits). The ends of the conduits must be bonded with the corresponding terminal. However, it is also possible to turn the enclosure of the devices into local lightning protection zones which are either connected with unshielded lines, and must then be protected at the zone interfaces, or with shielded lines forming a common protection zone for lines and devices.
Sources HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’ (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach; fourth edn, 1993)
4.1.3.2 Realization of LEMP protection This step of the LEMP-protection management process, coming after the LEMP-protection planning, includes the following: of survey diagrams and descriptions • preparation working out of tender specifications • making of detailed drawings and flow diagrams for the installation. • These works can be carried out by an electrotechnical engineering office. Here, for example, it will be specified how the connection of the incoming metal piping to the reinforcement, at the interface of lightning protection zones 0A and 1, has to be carried out to conduct lightning current and be EMC-compliant. Or, it will be indicated how metal stages, cabinets, enclosures and cable racks are to be included into the meshed functional equipotential bonding in rooms containing information technology systems and equipment (Figure 4.1.3.2 a). Cable lists (and types), number of wires, handling of the shield, electrical and mechanical interface configurations, operating voltages, transmission frequencies, backup fuses etc., have to be indicated. Also, the test values of the arresters used
98
Overvoltage protection of low voltage systems
Figure 4.1.3.1.6 c
Measures of shielding and optimal cable routing
for the bonding of lines at the interfaces of the lightning protection zones must be stipulated (Table 4.1.3.2 a). The arresters provided within a scheme using the concept of lightning protection zones are connected in series in the respective cable run. Therefore, the output levels of the arresters must be stipulated in such a way that the coordination with the downstream arrester or device or system (characterized by its basic strength) is guaranteed, and that the prospective system short-circuit currents can be controlled.
Protective measures, standards 99
Figure 4.1.3.2 a Table 4.1.3.2 a
Meshed functional equipotential bonding at a cabinet entry Typical test values of arresters installed at the line interfaces of lightning protection zones
Basically, the planner is free to determine how best to use and coordinate the arresters and devices or systems, as long as it is guaranteed that interference will be reduced to levels below the basic strength of the devices or systems to protect in the respective lightning protection zones. 4.1.3.3 Installation and supervision of LEMP protection Essentials of this step of LEMP-protection management are: assurance at the installation • quality documentation • revision of detailed drawings. •
100
Overvoltage protection of low voltage systems
It is here that system builders, lightning protection experts, engineering officers, and the supervising authority cooperate or liaise. If, for example, structural steel mats are bonded by means of hotgalvanized steel strips, steel wires and clamps (Figure 4.1.3.3 a), control is easily possible by inspection and photodocumentation. In the case of lightning current arresters for power technical systems (installed at the interface of lightning protection zone 0A and 1, Figure 4.1.3.3 b), care must be taken to carry out professional installation (e.g., for expulsion arresters a sufficient separation must be maintained between neighbouring live bare parts). In the case of lightning current arresters for information technology lines, special attention must be paid to the separate installation of the lines coming from lightning protection zone 0A and those leading into lightning protection zone 1 (Figure 4.1.3.3 c). In larger systems it is useful to install protection cabinets (Figure 4.1.3.3 d) as a central interface between two lightning protection zones. 4.1.3.4 Acceptance inspection of the LEMP protection An independent lightning protection expert or a supervising authority will carry out the control and documentation of the system state at the acceptance inspection stage of the LEMP protection.
Figure 4.1.3.3 a Floor reinforcement with supportreinforcement bonded by wires/strips and clamps
Figure 4.1.3.3 b Lightning current arresters for the power technical line at the transition from lightning protection zone OA into lightning protection zone 1
Protective measures, standards 101
Figure 4.1.3.3 c Lightning current arresters for the information technology line (lightning protection zone OA → lightning protection zone 1)
Figure 4.1.3.3 d Protective cabinet with connected cable shields and arresters
4.1.3.5 Periodic inspection To safeguard the reliability performance of the protection system it is necessary that lightning protection experts or supervising authorities make periodic inspections. The standard draft DIN VDE 0185 Part 110: 1997-01 ‘Blitzschutzsystem. Leitfaden zur Prüfung von Blitzschutzsystemen’ (‘Lightning protection system. Guide for testing lightning protection systems’) describes the kind of tests, test turns, test measures and the documentation involved.
Sources DIN V VDE V 0185-110 (VDE V 0185 Teil 110):1997-01: ‘Blitzschutzsysteme. Leitfaden zur Prüfung von Blitzschutzsystemen’ (VDE Verlag, GmbH, Berlin/ Offenbach, Jan. 1992)
4.1.3.6 Costs The requirement that information technology electronic systems must not be damaged by electromagnetic interference due to direct or close-up lightning strikes has led to a new quality and dimension of lightning
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Overvoltage protection of low voltage systems
protection engineering. The correspondingly developed concept, embodied in DIN VDE 0185-103 (VDE 0185 Part 103), lightning protection zones (Figure 4.1.3.6 a) has turned out to be a very efficient management method in complex and manifold problems; it has also been proven as a universal organizing principle: for example, computing centres, administration buildings, control and instrumentation technical systems, power plants including solar and wind power plants, telephone central offices, radar systems and main transmitters. Also the costs of EMC-compliant lightning protection can be calculated from the many existing projects. In the case of newly-built largescale projects, about 0.5% max. to 1% of the gross building cost must be allocated to achieve an effectiveness of protection of about 99%. In subsequent installation and retrofitting, the costs will increase by a factor of 10 and the effectiveness of protection reduces to 95–90%.
Sources HASSE, P., and WIESINGER, J.: ‘Requirements and tests for EMC-oriented lightning protection zones’, etz, DEHN publication, reprint from 1990, No. 21, pp. 1108–1115 HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’ (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach; 4. Auflage, 1993) HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept’ (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach, 1994) HASSE, P., WIESINGER, J., ZAHLMANN, P., and ZISCHANK, W.: ‘A future-
Figure 4.1.3.6 a
Concept of lightning protection zones
Protective measures, standards 103 oriented principle for the coodination of arresters in low-voltage systems’, DEHN publication, reprint from etz, 1995, No. 1, pp. 20–23 HASSE, P.: ‘Blitzschutz-Management – Planung und Organisation. 1st VDE/ ABB-Blitzschutztagung “Blitzschutz für Gebäude und Elektrische Anlagen” ’ (29 Feb.–1 March 1996, Kassel) WETTINGFELD, J.: ‘Was ist neu in ENV 61024-1/01.95 (DIN VDE 0185 Teil 100)? 1st VDE/ABB-Blitzschutztagung “Blitzschutz für Gebäude und Elektrische Anlagen” ’, (29 Feb.–3 March 1996, Kassel) STEINBIGLER, H.: ‘Verfahren und Komponenten des Gebäudeblitzschutzes. 1st VDE/ABB-Blitzschutztagung “Blitzschutz für Gebäude und Elektrische Anlagen” ’ (29 Feb.–1 March 1996, Kassel) WIESINGER, J.: ‘Was ist neu in IEC 1312-1/02.95 (DIN VDE 0185 Teil 103)? 1st VDE/ABB-Blitzschutztagung “Blitzschutz für Gebäude und Elektrische Anlagen” ’ (29 Feb.–1 March 1996, Kassel) KERN A.: ‘Blitz-Schutzzonen mit Schirmungen und Schnittstellen. 1st VDE/ ABB-Blitzschutztagung “Blitzschutz für Gebäude und Elektrische Anlagen” ’ (29 Feb.–1 March 1996, Kassel) PUSCH, H., and RAAB, V.: Gebäudeblitzschutz – Neue Europanorm. TAB, 1996, 12, pp. 69–73 HASSE, P.: ‘Blitzschutz für Gebäude und Elektrische Anlagen – 1’, VDE/ABBBlitzschutztagung, 1996, 11, pp. 960–964; 1996, 12, pp. 1107–1112 MÜLLER, K.-P.: ‘Neue Blitzschutznormung’, Elektropraktiker, 1996, 6 DIN VDE 0185: ‘Blitzschutzanlage – Teil 1: Allgemeines für das Errichten – Teil 2: Errichten besonderer Anlagen’ (VDE Verlag, GmbH, Berlin/ Offenbach, Nov. 1982) IEC 61024-1: ‘Protection of structures against lightning. Part 1: General principles’. International Electrotechnical Commission, Genève, March 1990 IEC 61312-1: ‘Protection against lightning electromagnetic impulse. Part 1: General principles’. Central de la Commission Electrotechnique Internationale, Genève, Feb. 1995 IEC 61662: ‘Assessment of the risk of damage due to lightning’. Bureau Central de la Commission Electrotechnique Internationale, Genève, April 1995 DIN V ENV 61024-1(VDE V 0185 Teil 100): 1996-08: ‘Blitzschutz baulicher Anlagen. Teil 1: Allgemeine Grundsätze (IEC 61024-1: 1990, modifiziert)’ (VDE Verlag GmbH, Berlin/Offenbach, Aug. 1996) DIN VDE 0185-103 (VDE 0185 Teil 103): 1997–09: ‘Schutz gegen elektromagnetischen Blitzimpuls (LEMP). Teil 1: Allgemeine Grundsätze. Identisch mit IEC 81(Sec)44’ (VDE Verlag, GmbH, Berlin/Offenbach, Sept. 1997)
4.2 Surge protection for electrical systems of buildings, IEC 60364, DIN VDE 0100 A detailed treatment of the surge protection of buildings is given in IEC/TC 64. Corresponding international standards in IEC 60364 are provided in chapter 44 of the publication. Part 440 is the relevant chapter in the national standard series DIN VDE 0100.
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Chapter 44 of the above document is divided as follows: Chapter 44 Protection in case of surges Section 441 General Section 442 Protection of low-voltage systems in case of earth faults in systems with higher voltage Section 443 Protection against surges due to atmospheric influences Section 444 Protection against electromagnetic interference in systems of buildings. Also relevant from IEC 60364 (chapter 53) is the following section: Section 534 Selection and installation of surge protection facilities.
4.2.1 IEC 60364-4-443/DIN VDE 0100 Part 443 The current document IEC 60364-4-443: 1995-04 ‘Publication 364: Electrical installations of buildings; Part 4: Protection for safety; Chapter 44: Protection against overvoltage; Section 443: Protection against overvoltages of atmospheric origin’/ DIN VDE 0100 Teil 443 ‘Errichten von Starkstromanlagen mit Nennspannungen bis 1000 V Schutzmassnahmen Schutz gegen Überspannung infolge atmosphärischer Einflüsse’ contains the following statement: “These standard requirements are provided for describing measures which limit transient overvoltages, in order to reduce the risk of faults in the system and the connected equipment, to an acceptable dimension. This procedure is in agreement with the principles of the insulation coordination in the Publication IEC 664 ‘Insulation coordination in lowvoltage systems and equipment’. “Overvoltage categories are intended for distinguishing different degrees of availability of the equipment. Availability of equipment is differentiated according to the demands concerning continuity of operation and acceptable risk of faults, damage and failures. In connection with the preferred surge resistance level of the equipment, they allow a suitable insulation coordination of the whole system to be achieved, which reduces the risk of faults/failures to an acceptable level/limit and are a basis for a surge protection (regulation). “A higher reference number of the overvoltage category indicates a higher specific surge resistance of the equipment, and means at the same time a wider choice of surge regulation/protection methods.” In the above standard, environmental conditions AQ 1 to AQ 3 are defined upon which the application of surge arresters depends. Classifications with regard to the effect of lightning are: AQ 3: direct effect of lightning (cross reference to IEC 61024-1) AQ 2: indirect effect of lightning, danger from the supply system AQ 1: negligible effect of lightning.
• • •
Protective measures, standards 105
Sources IEC 60364-4-443: ‘Electrical installation of buildings – Part 4: Protection for safety (chapter 44): Protection against overvoltages (Section 443): Protection against overvoltages of atmospheric origin or due to switching’. Bureau Central de la Commission Electrotechnique Internationale, Genève, April 1987 E DIN VDE 0100 Teil 443: 1987-04: ‘Errichten von Starkstromanlagen mit Nennspannungen bis 1000 V. Schutzmassnahmen; Schutz gegen Überspannungen infolge atmosphärischer Einflüsse. (Identisch mit IEC 64(CO)168’ (VDE Verlag, GmbH, Berlin/Offenbach, April 1987)
4.2.2 IEC 60664-1/DIN VDE 0110 Part 1 IEC 60664-1 ‘Insulation coordination for equipment within low-voltage systems. Part 1: Principles, requirements and tests’ became valid in 1992. In Germany DIN VDE 0110-1 (VDE 0110 Part 1) is valid: 1997-04 ‘Isolationskoordination für elektrische Betriebsmittel in Niederspannungsanlagen. Teil 1: Grundsätze, Anforderungen und Prüfungen (IEC 60664-1: 1992, modified).’ In this standard the insulation coordination for equipment in low-voltage systems is specified. It is valid for equipment having a rated alternating voltage up to 1000 V, with nominal frequencies up to 30 kHz, or a rated direct voltage up to 1500 V. Therein are defined the following: (a) Insulation coordination: Reciprocal classification of the insulation characteristics of electrical equipment, under consideration of the expected microenvironmental conditions and other important stresses. (b) Surge withstand voltage: Maximum value of the surge voltage of conventional shape and polarity which does not lead to puncture or sparkover of the insulation under specified conditions. (c) Rated surge voltage: Value of a surge withstand voltage, indicated by the producer for an equipment or a part of it, indicating the specified withstand capability of the respective insulation with regard to periodic peak voltages. (d) Overvoltage category: A numerical value that specifies a surge withstand voltage. Note: Overvoltage categories termed I, II, III, and IV are used. (e) State of limited overvoltage: State within an electric system where the expected transient overvoltages remain limited to a specified height. In this standard the principles of the ‘insulation coordination’ are specified as follows: Insulation coordination comprises the selection of the electrical insulation characteristics of a piece of equipment, regarding its application and its surroundings. Insulation coordination can only
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be achieved if the rating of the equipment is based on the stress to which it will be exposed during its probable lifetime. With respect to ‘transient overvoltages’ it points out that insulation coordination regarding transient overvoltages is based on a state of limited overvoltages. There are two kinds of limitation: limitation. The state within an electrical system where, • In-system due to the characteristics of the system, it can be assumed that
•
the expected transient overvoltages remain limited to a specified height. Protective limitation. The state within an electrical system where, due to the use of special overvoltage limiting means, it can be assumed that the expected transient overvoltages will be limited to a specified height.
Note 1: Overvoltages in large and complex systems, such as low-voltage systems that are exposed to multiple and changing influences, can only be judged on a statistical basis. This applies especially for overvoltages of atmospheric origin, as well as if the limitation is achieved due to an in-system limitation, or to a protective limitation. Note 2: An examination concerning the probability as to whether an in-system limitation exists or whether a protective limitation will be necessary, is recommended. This examination requires knowledge of the electrical system data, of the keraunic level, the height of the transient overvoltage etc. (This examination procedure is applied in IEC 60364-4-443 for power systems in buildings which are connected to low-voltage systems.) Note 3: The special overvoltage limiting means may contain components for storage or discharging of energy and are able to safely discharge the energy of the overvoltages expected at the place of installation. To apply the principle of insulation coordination, two different kinds of transient overvoltages must be considered: overvoltages originating from the system to • Transient equipment is bonded by its terminals. • Transient overvoltages originating from the equipment.
which the
This basic safety standard explains to ‘technical committees’ (i.e., those who are responsible for the standardization of different equipment) how the insulation coordination can be achieved. For the purpose of sizing equipment in accordance with the insulation coordination, such technical committees must specify an overvoltage category according to the probable use of the equipment, under consideration of the system parameters for the connection of which it is provided. The overvoltage categories are a means of maintaining the operation of
Protective measures, standards 107
devices in accordance with the necessary requirements, and differentiating between the degrees of availability with regard to a possible risk of failure. In connection with special values of the ‘surge withstand voltage’ for devices, the categories enable a suitable insulation coordination in the whole installation; they are the basis for the limitation of overvoltages so that the risk of failure can be reduced to an acceptable value. A higher numerical value of the overvoltage category indicates a higher ‘surge withstand capability’ of the device and offers a wider choice of methods of surge limitation. The principle of the overvoltage categories is applied for equipment that is directly supplied by the low voltage system. Application of overvoltage categories is based on the surge protection requirements contained in IEC 60364-4-443. (Note: Atmospheric overvoltages mostly are not weakened in the course of the installation.) Examinations have shown that a probability oriented concept is suitable as described in the following: Determination of an overvoltage category for directly supplied system equipment must be realized on the basis of the following general description: category I equipment is intended for connection to the • Overvoltage fixed electrical installation of a building. Outside the device measures
• •
•
have been taken, either in the fixed installation or between the fixed installation and the device, in order to reduce the transient overvoltages to the respective value. Overvoltage category II equipment is intended for connection to the fixed installation of a building. (E.g., devices include household appliances, portable tools and items of similar loading.) Overvoltage category III equipment is part of the fixed installation, and other devices, where a higher degree of availability is expected. (E.g., devices include distribution boards, circuit-breakers, distributions (IEV 826-06-01, including cables, bus bars, distribution cabinets, switches, socket outlets) in the fixed installation and devices for industrial use, as well as other devices, such as stationary motors with permanent connection to the fixed installation.) Overvoltage category IV equipment is intended for use at or near the feed into the electrical installation of buildings, and that from the main distribution into the direction of the system. (E.g., devices include electricity meters, overcurrent circuit-breakers and ripplecontrol units.)
The rated surge voltage of the equipment is given in Table 4.2.2 a according to the determined overvoltage category and the rated voltage of the equipment. (Note that equipment with a special rated surge voltage, having more than one rated voltage, may be suitable for different overvoltage categories.)
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Table 4.2.2 a
Rated impulse voltage for equipment (energized directly from the low-voltage mains)
For equipment that can generate overvoltages at the terminals of the equipment (e.g., switchgear) the rated surge voltage means that the equipment must not generate overvoltages exceeding this value; that is, if it is operated in accordance with the respective standard and the instructions of the producer. (Note that there is always a residual risk that overvoltages may be generated that exceed the value of the rated surge voltage, depending on the conditions of the circuit.) Equipment operating under the conditions of a higher overvoltage category is allowed provided that a suitable surge limitation is enforced. Suitable surge damping can be attained by using: protective installation • aa surge transformer separated windings • a distribution with system a multitude of branches (which are able to • discharge the energy ofwith surges) which is able to charge up to the energy of surges • aa capacitance resistance or similar damping elements which are able to discharge • the energy of surges. It should be taken into account that every surge protective installation within the system or the equipment might have to discharge more energy than a surge protective installation at the connection point of the system, if the latter has a higher operating voltage.
Protective measures, standards 109
4.2.3 IEC 60364-5-534 / DIN VDE 0100 Part 534 During the preparation of this book (starting in January 1997) both standard drafts: DIN IEC 64/867/CDV (VDE 0100 Part 534):1996-10 ‘Electrical • Einstallations of buildings – Selection and Erection of electrical equip-
•
ment – Switchgear and controlgear – Devices for protection against overvoltages (IEC 64/867/CDV: 1996)’ E DIN VDE 0100-534/A1 (VDE 0100 Part 534/A 1):1996-10 ‘Electrical installations of buildings – Selection and Erection of electrical equipment – Switchgear and controlgear – Devices for protection against overvoltages – Amendment A1 (proposal for a European standard)’
were available. The aforementioned IEC standard draft has now been refused by the German DKE subcommittee UK 221.3 ‘Protection Measures’ on the grounds that its aim no longer meets the current technical state and is, therefore, of no assistance in the erection of surge-protective installations. The main reason for this refusal is the fact that the surge protection must not only consider switching operations and remote lightning strikes (IEC 61024/61312-1), but also it must consider close-up or direct lightning interference (IEC 61024/61312-1). Thus, it is necessary to cater for in a single standard not only the selection and installation of arresters for lightning protection, but also surge protection. Today, the accepted state of engineering is such that a complex lightning/surge protection system requires more than one type of arrester. Taking this requirement into account, three arrester types (classes I, II and III) with different protection capacities are standardized in the relevant product standard DIN IEC SC 37A/44/CDV (VDE 0675 Part 6A1). A multistage protective concept, realized by means of these different types of arresters, includes not only surge protection but also protection against direct lightning strikes. A second standard draft, prepared by the German UK 221.3, is proposed for the development of the above-mentioned IEC paper. The suggested main section 534 of ‘Einrichtungen zum Schutz bei Überspannungen’ treats, on the one hand, the selection and the installation of protective equipment for the surge protection due to indirect atmospheric discharges and switching operations according to IEC 60364-4-443 (according to DIN VDE 0100-443 (VDE 0100 Part 443) ) and, on the other hand, the selection and the installation of protective equipment due to lightning currents and surges in connection with direct lightning strikes and lightning strikes in the vicinity of buildings according to IEC 61024-1 and IEC 61312-1. Thus, the regulations for the selection and the installation of the
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protective equipment and their compatibility with the protective measures against electric shock applied in the system are presented in one principle section of the erection standard for low voltage systems. These standard drafts, however, are not under discussion and so they will not be considered further. Nevertheless, the description of the different application possibilities of arresters in the power technical system (given in chapter 5.8.1.6.2) refers to this German draft.
Sources HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’ (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach; Fourth edn, 1993) E DIN IEC 64(Sec)675 ( VDE 0100 Teil 443/A3): ‘Errichten von Starkstromanlagen mit Nennspannungen bis 1000 V – Schutzmassnahmen. Schutz bei Überspannungen infolge atmosphärischer Einflüsse und von Schaltvorgängen’, Oct. 1993 IEC 60364-4-443: ‘Electrical installation of buildings – Part 4: Protection for safety (chapter 44): Protection against overvoltages (Section 443): Protection against overvoltages of atmospheric origin or due to switching’, April 1995 E DIN IEC 64/867/CDV (VDE 0100 Teil 534): ‘Elektrische Anlagen von Gebäuden – Auswahl und Errichtung elektrischer Betriebsmittel – Schaltgeräte und Steuergeräte – Überspannungs-Schutzeinrichtungen. (VDE Verlag, GmbH, Berlin/Offenbach, Oct 1996 E DIN VDE 0100-534/A1 (VDE 0100 Teil 534/A 1): Elektrische Anlagen von Gebäuden – Auswahl und Errichtung von Betriebsmitteln – Schaltgeräte und Steuergeräte – Überspannungs-Schutzeinrichtungen – Änderung A1 (Vorschlag für eine Europäische Norm). (VDE Verlag, GmbH, Berlin/Offenbach, Oct. 1996) DIN VDE 0110-1 (VDE 0110 Teil 1): Isolationskoordination für elektrische Betriebsmittel in Niederspannungsanlagen. Teil 1: Grundsätze, Anforderungen und Prüfungen (IEC 664–1: 1992, modifiziert) (VDE Verlag, GmbH, Berlin/Offenbach, April 1997)
4.3 Surge protection for telecommunications systems, DIN VDE 0800, DIN VDE 0845 DIN VDE 0800 Part 1: 1989-05 ‘Fernmeldetechnik – Allgemeine Begriffe, Anforderungen und Prüfungen für die Sicherheit der Anlagen und Geräte’ (‘Telecommunications – General concepts, requirements and tests for the safety of facilities and apparatus’). The scope of application of this VDE regulation refers to the safety of the facilities and apparatus of telecommunication engineering (in the following: telecommunication systems and telecommunication devices) with regard to the prevention from danger to life or health (of people and animals) and
Protective measures, standards 111
things. This standard is also applicable for the safety of information or data processing systems for which no other standards are valid. DIN VDE 0800 Part 2: 1985-07 ‘Erdung und Potentialausgleich in der Fernmeldetechnik’. (‘Telecommunications; earthing and equipotential bonding’.) The following is quoted regarding the treatment of ‘line shields’ (i.e., a shield out of conductive material which accompanies the lines in a certain geometric form) and the integration of steel constructions or reinforcements: the version as an electromagnetic screen (according to DIN IEC • In 60050 Part 151: 1983-12, section 151-01-16) the line shield can con-
•
tribute to equipotential bonding, as both of its ends are connected to a reference potential. Integration of steel constructions and reinforcements into the earthing system. If there are particularly high demands on the earthing system of a building regarding the function, in order to avoid potential differences between different points of the building and thereby cause equalizing currents, measures should be taken to include the steel construction and the reinforcement into the earthing system. For this purpose the reinforcement shall be connected with the earth bus bar, if the components of the reinforcement are continuously connected. Equalizing currents in the reinforcement, in parallel with equipotential bonding conductors between points of different potential, can lead to interference in the telecommunication system if, because of excessive impedance, an inadmissible coupling with telecommunication circuits occurs, or contact resistances are submitted to fluctuations. The continuous connection of the reinforcement, for example, can be realized by welding or careful lashing. If, owing to the statics, welding is not possible, additional steel structures should be put in place, which must be welded to each other and lashed to the reinforcement. The continuous connection of the building reinforcement is (even in the case of buildings made out of prefabricated parts) only possible during the erection of the building. Equipotential bonding by steel constructions and reinforcement must therefore already be taken into consideration at the planning stage of the foundations and the building construction.
DIN VDE 0845 Part 1: 1987-10 ‘Schutz von Fernmeldeanlagen gegen Blitzeinwirkungen, statische Aufladungen und Überspannungen aus Starkstromanlagen – Massnahmen gegen Überspannungen’. The scope of application is quoted as follows: standard is valid for measures against dangerous or interfering • This surges in telecommunication systems. These surges are caused by electromagnetic interference or by lightning effects or static charges.
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Thereby also the devices and transmission lines belonging to the telecommunication system are taken into consideration. For external lightning protection (the interception and downconduction of lightning currents) DIN VDE 0185 Part 1 is applicable, and for aerial systems DIN VDE 0855 Parts 1 and 2.
Sources HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’ (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach; Fourth edn, 1993) DIN VDE 0800 Teil 1: ‘Fernmeldetechnik. Allgemeine Begriffe, Anforderungen und Prüfungen für die Sicherheit der Anlagen und Geräte’ (VDE Verlag, GmbH, Berlin/Offenbach, May 1989) DIN VDE 0800 Teil 2: ‘Fernmeldetechnik. Erdung und Potentialausgleich’ (VDE Verlag, GmbH, Berlin/Offenbach, July 1985) DIN VDE 0845 Teil 1: ‘Schutz von Fernmeldeanlagen gegen Blitzeinwirkungen, statische Aufladungen und Überspannungen aus Starkstromanlagen. Massnahmen gegen Überspannungen’ (VDE Verlag, GmbH, Berlin/ Offenbach, Oct. 1987)
4.4 Electromagnetic compatibility including protection against electromagnetic impulses and lightning, VG 95 372 The standard VG 95 372: 1996–03 gives a survey of the VG standards for electromagnetic compatibility (EMC) including protection against electromagnetic impulses (EMP) and lightning. A tabulated list for EMC is given in Figure 4.4 a.
Source VG 95 372: ‘Elektromagnetische Verträglichkeit (EMV) einschliesslich Schutz gegen den Elektromagnetischen Impuls (EMP) und Blitz – Übersicht’. (Beuth Verlag, GmbH, Berlin, March 1996)
4.5 Standards for components and protective devices International (IEC) as well as regional (Cenelec) standardizing work on components for lightning protection systems and surge protective devices has now progressed. National (DIN VDE) standards and drafts with testing authorization are also available. These standards shall be considered in the following only as far as it is necessary for the understanding of the mode of function and the possibilities of using these components and protective gear.
Protective measures, standards 113
4.5.1 Connection components, E DIN EN 50164-1 (VDE 0185 Part 201) For lightning protection components (terminals, connectors) the standard draft E DIN EN 50164-1 (VDE 0185 Part 201) ‘Lightning protection components. Part 1: Requirements for connection components’ has been available since May 1997. This specifies the requirements and tests for lightning current conductive connection components. This standard will eventually replace the national DIN-regulation DIN 48 810/8.86. The standard draft E DIN EN 50164-1 is currently under revision by the European Standardizing Committee (Cenelec). In addition to conditioning/ageing considerations (simulation of corrosion stress arising in practice) the standard also includes a test by lightning currents (10/350 μs), which is as follows: Corresponding to their classification indicated by the producer, the connection components are classified as H and L and tested accordingly: H (high loading) L (normal loading)
test current 100 kA (10/350 μs) test current 50 kA (10/350 μs)
Criteria for the passing of the lightning current tests are, for example, a sufficiently low contact resistance, no perceptible damage, deformation or loose parts as well as requirements for the release torque of the screwed connection parts.
4.5.2 Arresters for lightning currents and surges A difference is made between lightning current arresters (tested by surge currents of wave shape 10/350 μs) and surge arresters (tested by surge currents of wave shape 8/20 μs). 4.5.2.1 Arresters for power engineering, IEC 61643-1/E DIN VDE 0675 Part 6 The German standard draft E DIN VDE 0675 Part 6 ‘Surge arresters for use in AC supply systems with nominal voltages ranging from 100 V to 1000 V’ has been available since 1989. In March 1996 E DIN VDE 0675-6 A1 (VDE 0675 Part 6/A1) ‘Amendment A1 to the draft DIN VDE 0675-6 (VDE 0675 Part 6)’ with testing authorization was published and in October 1996 E DIN VDE 0675-6/A2 (VDE 0675 Part 6/A2) ‘Amendment A2 to the draft DIN VDE 0675-6 (VDE 0675 Part 6)’. Also in October 1996 DIN IEC 37A/ 44/CDV (VDE 0675 Part 601) ‘Surge protective devices for low-voltage distribution systems. Part 1: Performance requirements and testing methods (IEC 37A/44/CDV: 1996)’ was introduced. This later IEC standard was valid in February 1998 as IEC 61643-1 ‘Surge protective devices connected to low-voltage distribution systems, Part 1: Performance
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requirements and testing methods’. The activities of the IEC SC 37A committee which is competent for the international standardization of arresters are shown in Figure 4.5.2.1 a. The yellow printed E DIN VDE 0675 Part 6/A1 is based on the draft DIN VDE 0675 Part 6/1989-11. The categories and classifications of the arrester types have been mostly retained. These arresters are subdivided into four requirement classes:
Protective measures, standards 115
Figure 4.4 a
Survey of the VG-standards for EMC including protection against EMP and lightning
A. Arresters which are installed in low voltage overhead lines • Class and at places where they cannot be touched. Testing is made with
• • •
surge currents of wave shape 8/20 μs (Figure 4.5.2.1 b). Class B. Arresters installed for the purpose of lightning protection equipotential bonding and controlling direct lightning strikes. These arresters are tested by a simulated lightning test current Iimp of wave shape 10/350 μs (Figure 4.5.2.1 b). Class C. Arresters installed for the purpose of surge protection in the fixed installation, for example, in the distribution area. These arresters are tested by the nominal discharge surge current isn of wave shape 8/20 μs (Figure 4.5.2.1 b). Class D. Arresters installed for the purpose of surge protection in the fixed or mobile installation, especially in the socket outlet area or before terminals. For testing this arrester group, a hybrid generator
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Overvoltage protection of low voltage systems
Figure 4.5.2.1 a
Standardization in IEC SC 37A ‘Low-voltage surge protective devices’
Figure 4.5.2.1 b
Comparison of test currents for surge protective devices (SPDs)
(with an apparent interior resistance 2 Ω) generating an open-circuit surge voltage 1.2/50 μs and a short-circuit surge current 8/20 μs is used. The open-circuit voltage Uoc of the hybrid generator, used for testing, is indicated as a parameter for these arresters. The tests/amendments in Part A1 concern above all the electrical requirements and test procedures, which will be briefly explained in the following as far as it is relevant for the user:
Protective measures, standards 117
(a) Lightning test current (Iimp) for class B arresters The lightning test current Iimp (10/350 μs) replaces the former lightning test current of wave shape 8/80 μs (Figure 4.5.2.1 b). Iimp is determined by the following parameters: peak value (Ipeak), charge (Q), specific energy (W/R), and wave shape (10/350 μs). For the wave shape the value 10 indicates a front rise time of 10 μs and 350 μs the time to the half-value in a wave tail of 350 μs of the lightning wave. The lightning test current Iimp of the wave shape 10/350 μs conforms most closely with the first surge current of natural lightning discharges and is used worldwide for lightning simulation. (b) Determination of the measured limiting voltage: Protection level Up The testing procedure to determine the measured limiting voltage is subdivided according to the type and class of the arrester. The measured limiting voltage is the highest value from differently carried out tests. The protection level, which has been determined with reference to the insulation coordination, must not be exceeded by the measured limiting voltage. (c) Conditioning and operating duty test, discharge capacity Here the performance of the arresters regarding their discharge and follow-current quenching capacity is tested (see Figure 4.5.2.1 c). Now that the interior structure of the arrester is known, a source of voltage corresponding to its follow current is chosen (Table 4.5.2.1 a) and conditioned in accordance with its requirement class: A, B and C ⇒ 15 surge currents 8/20 μs with isn D ⇒ 15 combined surges 1.2/50 μs /8/20 μs with Uoc/2 Ω
On testing the operating duty, the arrester will be submitted to five surge currents, according to its class, in steps up to the maximum value, whereby its thermal stability will be controlled:
• • •
A, C surge currents up to Imax (maximum discharge surge current 8/20 μs) B surge currents up to Iimp (lightning test current 10/350 μs) D combined surge up to Uoc/2 Ω
(d) Disconnecting device for arresters and thermal stability of arresters On testing the disconnecting device and the thermal stability of arresters, a difference is generated, whether a spark gap covered arrester or an arrester based on a varistor is concerned. The difference is generated to obtain a practice-like simulation of possible causes of fault:
•
Arresters based on varistors. It is assumed that, over the course of years, the leakage current will increase due to repeated surge
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Overvoltage protection of low voltage systems
Figure 4.5.2.1 c
•
Flow diagram ‘operating duty test’
current loadings. This leads to a heating or increased power loss in the arrester. This ‘thermal drift’ is simulated in the disconnection test. The disconnecting device must separate the arrester from the system before the enclosure becomes too hot which might present a fire hazard. Arresters with spark gaps or spark gaps in series. Here the assumed fault is that there are too frequent and too high discharge currents or too many follow-current quenching processes.The electrodes of the integrated spark gaps are welding and a short circuit is generated. On testing, this fault will be simulated by shortcircuiting spark gaps with a copper conductor. The maximum
Protective measures, standards 119
backup fuse certified by the producer must disconnect the arrester from the system before there is noticeable damage at the arrester or fire hazard due to the arrester. Table 4.5.2.1 a
Power frequency source of voltage for arrester conditioning: uc: continuous operating voltage of an arrester/rated voltage; IF: follow-current of the arrester; Ip uninfluenced short-circuit current
Sources IEC 61643-1: ‘Surge protective devices connected to low-voltage power distribution systems, Part 1: Performance requirements and testing methods’. Bureau Central de la Commission Electrotechnique Internationale, Genève, Feb. 1998
4.5.2.1.1 Important data for arrester selection voltage U . The value U indicates the maximum operating volt• Rated age the arrester is rated for and at which the certified performance data c
•
c
are met. Protection level Up. This parameter characterizes the ability of an arrester to limit interference to a non-dangerous voltage value Up. The required protection level of the arrester depends on the place of installation (overvoltage category) and/or on the electric strength of the device to be protected.
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Overvoltage protection of low voltage systems
capability. This parameter is of decisive importance if the • Discharge arrester must be selected according to the arising hazards (direct lightning strike, remote strike, induced surges). This value characterizes the real performance of the arrester and indicates the lightning test currents/surge currents/combined surges that can safely be discharged without disturbing its function considerably. This indication is also reflected in the arrester classification: Lightning test currents, Iimp ⇒ Class B Surge currents, isn or Imax ⇒ Class A, C Combined surge, Uoc ⇒ Class D
Breaking capacity/follow-current quenching capability I . This item is • important for spark-gap based arresters. It indicates the limit at which F
•
the system follow-current will be quenched automatically by the arrester. Disconnecting device/back-up fuse. These data are always of importance. This is particularly so if the arrester is overloaded or wrongly conceived, or aged due to a large number of discharges. Arresters designed according to E DIN VDE 0675-6/A1 are proving able to turn into a safe fault state in the case of an overload/defect on testing of the disconnecting device and thermal stability.
4.5.2.1.2 Coordination of the arresters according to requirements and locations. Figure 4.5.2.1.2 a and Table 4.5.2.1.2 a show the coordination of the arresters:
Figure 4.5.2.1.2 a
Application possibilities of arresters in the IEC-overvoltage categories
Protective measures, standards 121 Table 4.5.2.1.2 a
Selection help and assignment of arresters
B arresters (lightning current arresters). The location of the • Class lightning current arresters is the area of the house supply where high
• •
lightning partial currents may arise. Class C arresters. The typical location of these surge arresters is in the subdistribution. This is where the residual voltages of the lightning current arresters and surge currents (8/20 μs) in the kA range must be safely controlled. Class D arresters. These arresters are located either between the distributor and the terminal or at socket outlets.
With regard to the requirement for class D, rather than proceeding from an impressed surge current, the concern is for the voltage liable to cause danger Uoc; this will be limited to a low value. Typical values of dangerous voltages (arising at the terminal inputs, socket outlets) are in the range 2.5–4 kV. 4.5.2.1.3 N–PE arrester E DIN VDE 0675 Part 6/A2. In E DIN VDE 0675-6/A2 (VDE 0675 Part 6/A2): 1996–10 ‘Surge arresters. Part 6: Application in AC supply systems with nominal voltages ranging from 100 to 1 000 V. Amendment A2 for the draft DIN VDE 0675-6 (VDE 0675 Part 6)’ N–PE arresters are standardized. These will be installed between the neutral conductor (N) and the protective conductor (PE). What is the task of such N–PE arresters? For reasons of personal protection, class B and C arresters are usually installed (in energy flow direction) before a fault current circuit-breaker (also see chapter 5.8.6.1.2). To safeguard the disconnection of a faulty arrester by the back-up fuse in the TT-system, a ‘3 + 1-circuit’ is used. The three outer
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Overvoltage protection of low voltage systems
conductors L1, L2 and L3 are connected to arresters and then with the neutral conductor N. Between the neutral conductor N and the protective conductor PE, the N–PE arrester is installed. In the case of a defective (short-circuited) arrester (at the outer conductor), a shortcircuit current is generated between the concerned outer conductor L and the neutral conductor N which can be disconnected by the backup system fuse in the time provided. If the arresters were installed between L and PE, the current flowing in a TT-system over the defective arrester between L and PE would not be sufficient to trip the system fuse (further details in chapter 5.8.1.6.2.2). N–PE arresters must be able to conduct the sum of the interference currents of L1, L2 and L3 , towards N. For N–PE arresters the requirements listed in Table 4.5.2.1.3 a are valid. 4.5.2.2 Arresters for information technology, IEC SC 37A / E DIN VDE 0845 Part 2 Since October 1993, the German standard draft DIN VDE 0845 Part 2 ‘Schutz von Einrichtungen der Informationsverarbeitungs- und Telekommunikations-technik gegen Blitzentladung, Entladung statischer Elektrizität und Überspannungen aus Starkstromanlagen’. (‘Protection of Data Processing and Telecommunication Equipment Against Lightning Discharge, Electrostatic Discharge and Surges from Power Plants’) has been available. In this standard draft a difference is made between the following surge protective devices: Table 4.5.2.1.3 a
N–PE arrester. Voltages and currents in accordance with E DIN VDE 0675 Part 6/A2
Protective measures, standards 123
including: (i) surge arresters, gas-filled (or gas discharge tube); • gaps, (ii) creeping discharge arresters/air spark gaps; (iii) disconnecting
• • •
spark gaps; and (iv) quenching spark gaps semiconductor protective elements and varistors surge limiters protecting and isolating transformers, including reduction transformers.
As this list shows, the standard draft DIN VDE 0845 Part 2 covers components as well as surge protectors (surge limiters). In the international standardization (IEC), components and protectors are treated in separate standard drafts (Figure 4.5.2.1 a): specifications of the components (Components for low-voltage • The surge protection devices) are just being worked out by committee SC 37 B. At present there are four drafts: Draft IEC 61647-1: Specifications for gas discharge tubes (GDT) Draft IEC 61647-2: Specifications for avalanche breakdown diodes (ABD) Draft IEC 61647-3: Specifications for metal oxide varistors (MOV) Draft IEC 61647-4: Specifications for thyristor surge suppressors (TSS). specifications for surge protection devices are currently • The worked out by the committee SC 37 A / WG4. This is entitled:
being
IEC 61644-1: Surge protection devices connected to telecommunication and signalling networks. There are plans to work out a second part, describing the selection and the application of surge protectors. As the standardizing work is developed by committee SC 37 A, the requirements concerning tests of arresters for information technology and arresters for power technology will be ensured and coordinated with regard to their classes of requirement and the conditions of application. The yellow printed E DIN VDE 0845 Part 2 specifies requirements and tests made for surge protection devices to be used in installations of data processing and telecommunication technology. The user-relevant electrical requirements and tests for surge limiters are briefly explained later. For surge limiters, the standard draft identifies a difference between type 1 and type 2: namely, that type 1 surge limiters are provided for use against transient overvoltages (for example, caused by lightning), and that type 2 surge limiters are provided for locations where additional AC interference lasting up to 0.5 s must be taken into account.
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Overvoltage protection of low voltage systems
Source Entwurf DIN VDE 0845 Teil 2: ‘Schutz von Einrichtungen der Informationsverarbeitungs und Telekommunikationstechnik gegen Blitzeinwirkungen, Entladung statischer Elektrizität und Überspannungen aus Starkstromanlagen. Anforderungen und Prüfungen von Überspannungsschutzeinrichtungen’. (VDE Verlag, GmbH, Berlin/Offenbach, Oct. 1993)
4.5.2.2.1 Important data for arrester selection voltage U . The nominal voltage of an arrester serves for type • Nominal characterization and is usually identical to the nominal voltage of the N
• • •
system where the arrester will be used. Rated voltage Uc. The value Uc indicates the maximum operating voltage for which the arrester is rated, and where its specified performance data are met. This value is a support for the user in selecting an arrester for the maximum operating data of a system or equipment. Nominal current IN. The nominal current is the maximum admissible operating current that may be carried over a current path of an arrester. Operating frequency range. In the operating frequency range the arrester shows an insertion loss of 3 dB or less. As the arresters usually have a low pass characteristic, the operating frequency range is described by the cut-off frequency fG.
For use in digital transmission systems a special data transmission speed vs is required instead of an operating frequency range. The possible data transmission speed for an arrester is associated with the transmission procedure used in the system. This procedure determines the necessary cut-off frequency in a system with a low pass characteristic. In telecommunication engineering Vs = 2fG, or practically, for example, vs = 1.25 × fG. carrying capacity/discharge capability. Here the same criteria • Current are valid as for arresters for power engineering (see section 4.5.2.1a). The standard draft E DIN VDE 0845 Part 2 does not state any requirements for lightning current arresters (lightning test currents Iimp). In the present state of engineering there are also arresters for information technology equipment which are lightning current conductive (see chapter 5.8.2). Protection level U . In the standard draft E DIN VDE 0845 Part 2 this • value is also called the ‘maximum residual voltage’. This parameter p
characterizes the maximum voltage that can arise at the terminals of the arrester for the specified loadings. When selecting an arrester it must be borne in mind that this value is below the destruction limit of the subsequent device. Further selection criteria are described in chapter 5.8.2.
Protective measures, standards 125
Source Entwurf DIN VDE 0845 Teil 2: ‘Schutz von Einrichtungen der Informationsverarbeitungs und Telekommunikationstechnik gegen Blitzeinwirkungen, Entladung statischer Elektrizität und Überspannungen aus Starkstromanlagen. Anforderungen und Prüfungen von Überspannungsschutzeinrichtungen’ (VDE Verlag, GmbH, Berlin/Offenbach, Oct. 1993)
4.5.2.2.2 Arrester coordination according to requirements and locations A detailed coordination of the arresters for information technology equipment according to the requirements and locations is not given in the standard draft E DIN VDE 0845 Part 2. Only a subdivision into loading classes according to their current carrying capacity has been made. A practicable coordination of the arresters into classes of requirements and locations is described in chapter 5.8.2.
Source Entwurf DIN VDE 0845 Teil 2: 1993-10: ‘Schutz von Einrichtungen der Informationsverarbeitungs und Telekommunikationstechnik gegen Blitzeinwirkungen, Entladung statischer Elektrizität und Überspannungen aus Starkstromanlagen. Anforderungen und Prüfungen von Überspannungsschutzeinrichtungen’ (VDE Verlag, GmbH, Berlin/Offenbach)
4.5.2.3 Arrester coordination Now that classes of requirements and locations of the lightning current and surge arresters are known, the user or the project organizer must ensure the coordination of the arresters with regard to the devices to be protected. This is the only way to achieve optimally harmonized protection for systems and devices. In chapter 5.8.1.6.1, consideration is given to the graded use of arresters; the principle of energetic coordination will also be explained.
Sources HASSE, P., and ZÄUNER, E.: ‘Ableiter für Blitzströme und Überspannungen’, Neue VDE-Bestimmung, Auswahlhilfe für den Praktiker. de, 1996, H. 15 and 16, pp. 1397–1400 HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatz elektronischer Geräte auch bei direkten Blitzeinschlägen’ (Verlag TÜV Rheinland, Köln, 3. aktualisierte Auflage, 1993) E DIN VDE 0675 Teil 6: ‘Überspannungsableiter zur Verwendung in Wechselstromnetzen mit Nennspannungen zwischen 100 V und 1000 V’ (VDE Verlag, GmbH, Berlin/Offenbach, Nov. 1993)
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Overvoltage protection of low voltage systems
E DIN EN 50164-1 (VDE 0185 Teil 201): ‘Blitzschutzbauteile. Teil 1: Anforderungen für Verbindungsbauteile. Deutsche Fassung prEN 50164-1’ (VDE Verlag, GmbH, Berlin/Offenbach, May 1997) E DIN VDE 0675-6/A1 (VDE 0675 Teil 6/A1): ‘Überspannungsableiter zur Verwendung in Wechselspannungsnetzen mit Nennspannungen zwischen 100 V und 1000 V. Änderung A1 zum Entwurf DIN VDE 0675–6 (VDE 0675 Teil 6)’ (VDE Verlag, GmbH, Berlin/Offenbach, March 1996) E DIN VDE 0675-6/A2 (VDE 0675 Teil 6/A2): ‘Überspannungsableiter. Teil 6: Verwendung in Wechselspannungsnetzen mit Nennspannungen zwischen 100 V und 1000 V. Änderung A2 zum Entwurf DIN VDE 0675-6 (VDE 0675 Teil 6)’ (VDE Verlag, GmbH, Berlin/Offenbach, Oct.1996) E DIN IEC 37A/44/CDV (VDE 0675 Teil 601): ‘Überspannungsschutzgeräte für den Einsatz in Niederspannungs-Verteilungsnetzen. Teil 1: Anforderungen an ihr Betriebsverhalten und Prüfmethoden (IEC 37A/44/CDV: 1996)’ (VDE Verlag, GmbH, Berlin/Offenbach, Oct. 1996) E DIN VDE 0845 Teil 2 (VDE 0845 Teil 2) ‘Schutz von Einrichtungen der Informationsverarbeitungs und Telekommunikationstechnik gegen Blitzeinwirkungen, Entladung statischer Elektrizität und Überspannungen aus Starkstromanlagen. Anforderungen und Prüfungen von Überspannungsschutzeinrichtungen’ (VDE Verlag, GmbH, Berlin/Offenbach, Oct. 1993)
Chapter 5
Components and protective devices: construction, effect and application
In this chapter components and protective devices used for surge control and/or the realization of the EMC-oriented lightning protection zone concept will be introduced with particular regard to construction, mode of functioning and fields of application. These include: terminations for the erection of air-termination systems; in particu• Air lar, the protection of electrical installations on flat roofs against direct
• • • • • •
lightning strikes and thus assessing the lightning protection zone 0B. Materials and components serving for the erection of building and room shields for lightning protection zone 1 and higher. Materials and components by means of which it is possible to realize the shielding of power and telecommunication lines connecting neighbouring buildings. Shields for lines within lightning protection zone 1 and higher. Optoelectronic bondings. Components for equipotential bonding systems. Protective devices to discharge lightning currents and to limit overvoltages. Power and telecommunication lines, for example, are protected at the interfaces of the lightning protection zones by lightning current arresters, installed at the interface of lightning protection zones 0A and 1. Protective gear is also to be installed, for example, directly at the inputs of systems and devices, if they have their own (local) protection zones.
5.1 Air terminations Air terminations are fixed points for likely lightning strikes used to avoid uncontrolled strikes and to prevent the volume to be protected from
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Overvoltage protection of low voltage systems
direct strikes. Air terminations comprise air-termination rods and airtermination wires. The latter may be laid as a meshed network. The location of air terminations is usually defined by the ‘rolling sphere’ method (Figures 4.1.3.1.2 f a, b and c). This means that a certain radius of rolling sphere will be assigned to every protection level in accordance with DIN ENV 61024-1 (Table 4.1.1.b). Finally, air terminations form a system of protection for structures on the roof (such as ventilators and air-conditioning systems). On flat roofs ‘partly isolated’ lightning protection systems are usually installed as described in chapter 4.1.3. This air-termination system is spatially separated from lightning protection zone 1, so that there is a lightning protection zone 0B between the air-termination system and lightning protection zone 1 (Figures 4.1.3.1.2 b and d). For smaller roof structures this protection can be achieved by individual or a combination of several air termination rods. For larger roof structures protection by means of air termination rods is not often possible as the rods would be too high and thus there is danger of leaning. As an alternative an isolated air termination is the best solution. The distance between air terminations and structures on the roof must at least comform to the calculated safety distance. Air-termination networks must form a protective volume including all structures on the roof. Figures 5.1 a and b show examples of roof superstructures in lightning protection zone 0B.
Figure 5.1 a
Roof-ventilation cowl protected by an air-termination rod
Components and protective devices: construction, effect and application
Figure 5.1 b
129
Structures of air-conditioning systems protected by a mesh network
Sources HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach, 1994) DEHN u. SÖHNE Druckschrift: DS 626/0598 ‘Isolierte Blitz-Fangeinrichtungen’ (Dehne + SÖHNE, Neumarkt), May 1998
5.2 Building and room shields Extended metal components (e.g., metal roofs and facades, steel reinforcements in concrete, expanded metals in walls, lattices, metal supporting constructions, piping) which form an effective electromagnetic shield (see chapter 4.1.3, Figure 4.1.3.1.3 a) by their meshed interconnection (according to DIN VDE 0800 Part 2, DIN VDE 0185 Parts 1 and 103, DIN VDE 0845 Part 1) are especially important for shielding magnetic fields and for the creation of lightning protection zones. Figure 5.2 a shows how, in principle, a steel reinforcement and the metal window and door frames can form an electromagnetic cage (hole screen). In practice, however, it is not possible to weld or clamp every nodal point for large structures. The achievable shield attenuation or shielding factors of steel reinforcements are shown in Figure 5.2 b for the especially interesting frequency range of lightning interference from
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Overvoltage protection of low voltage systems
Figure 5.2 a
Room shield by means of steel reinforcement
Figure 5.2 b
Shielding effect of the reinforcement steel
100 Hz to 1 MHz. The damping indicated in this Figure is applicable for the case when a plain magnetic field influences the shield out of steel reinforcement. For estimation of the magnetic field strength at any point inside a lightning current-carrying cage structure, an approximation
Components and protective devices: construction, effect and application
131
formula is indicated in the draft of IEC 61312-2. The magnetic field strength depends mainly on the mesh size of the shield and on the distance from the shield (Figure 5.2 c). Figure 5.2 d shows how structural steel mats (e.g., concrete steel mats Q 377) in concrete are interconnected for shielding purposes by means of suitable clamps (Figures 5.2 e). Often, hot-galvanized steel conductors (round 10 mm dia. or flat 30 mm × 3.5 mm) are used for bonding the reinforcements (Figures 5.2 f and g). Thus, control (shortly before filling in the concrete) is easier. For bridging expansion joints or bonding the reinforcement of prefabricated concrete parts, fixed earthing terminals, shown in Figures 5.2 h and i, are provided. To such fixed earthing terminals or projecting bonding conductors (Figure 5.2 j) the ‘earth bus ’ or ‘earth ring bus’ (ring equipotential bonding bars) are connected (Figure 5.2 k). Metal facades (Figures 5.2 l and m) are also used for shielding purposes; the facade steel sheets, being interconnected, are to be bonded to the metal subconstruction and to the reinforcement (Figure 5.2 n). Some of the above-mentioned shielding measures can also be applied to the establishment of room shields (lightning protection zone 2 and higher). In particular this concerns the use of steel reinforcements (in floors, walls and ceilings), expanded metal (in walls and ceilings) and lattices. Smaller shields for lightning protection zones 2 and higher, or shields
Figure 5.2 c
Magnetic field strength as function of the wall distance and the mesh size of a grid structure
132
Overvoltage protection of low voltage systems
Figure 5.2 d
(a)
Figure 5.2 d
(b)
Figure 5.2 d
(a, b) Building shield out of interconnected structural steel mats and reinforcing rods
Components and protective devices: construction, effect and application
Figure 5.2 e
(a)
Figure 5.2 e
(b)
Figure 5.2 e
(c)
Figure 5.2 e
(d)
Figure 5.2 e
(a–d) Bonding of (overlapping) structural steel mats and reinforcing rods
Figure 5.2 f
Floor reinforcement bonded with support reinforcement by wires and clamps
133
134
Overvoltage protection of low voltage systems
Figure 5.2 g
(a)
Figure 5.2 g
(b)
Figure 5.2 g
(c)
Figure 5.2 g
(d)
Figure 5.2 g
(a–d) Clamps for the connection of bonding wires with the reinforcement
Figure 5.2 h
(a)
Figure 5.2 h Figure 5.2 h
(b)
(a and b) Fixed earthing terminal with connection to the reinforcement
Components and protective devices: construction, effect and application
Figure 5.2 i
Fixed earthing terminals for bridging the expansion joints
Figure 5.2 j
Brought out bonding wire of the reinforcing mats for connection to a ring equipotential bonding bar
Figure 5.2 k
‘Earth bus’ (according to DIN VDE 0800 Part 2)
135
136
Overvoltage protection of low voltage systems
Figure 5.2 l
Metal façade of an office building
Figure 5.2 m
Metal subconstruction for metal façade (Source: H. Neuhaus)
Figure 5.2 n
Down conductor system with connection to the air-termination system and to the earthing system with effective electromagnetic shielding
Components and protective devices: construction, effect and application
137
of local lightning protection zones, are usually formed by the enclosures (sheet steel cabinets, sheet steel covered racks, sheet steel enclosures) of telecommunication systems and devices (Figures 5.2 o and p).
Figure 5.2 o
Structure of an electronic cabinet
Figure 5.2 p
Connection of the baseframes for the electronic cabinets to the reinforcement of the building
Sources HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach, 1994)
138
Overvoltage protection of low voltage systems
MÜLLER, K.P.: ‘Wirksamkeit von Gitterschirmen, z.B. Baustahlgewebematten, zur Dämpfung des elektromagnetischen Feldes’. VDE-Fachbericht 52: Neue Blitzschutznormen in der Praxis (VDE Verlag Gmbh, Berlin/Offenbach, 1997)
5.3 Shields for lines between screened buildings In chapter 4.1.3.1.6 (Figure 4.1.3.1.6 a) it was shown how two spatially separated lightning protection zones can be changed into a single lightning protection zone by means of a line shield. The shields used will be introduced here as follows: of cables in metal conduits or closed trays which are con• Shielding nected on both sides at the building input (Figures 5.3 a and b). of buried cables with conductive shield which will be connected at • Use the building input (Figures 5.3 c and d). For protection against direct lightning strikes it may be useful to incorporate superimposed earth ropes.
Figure 5.3 a
Shielding of cables in metal conduits or closed trays
Components and protective devices: construction, effect and application
139
Figure 5.3 b
Steel conduits and metal pull boxes form a closed line screen
Figure 5.3 c
Shielding of underground cable routes by conductive screens and surface laid copper-ropes
Figure 5.3 d
Cable with external ‘lightning protection’ screen, core pair screen and pairing
140
Overvoltage protection of low voltage systems
of cage-shaped reinforced cable ducts, if a multitude of con• Erection ventional cables (e.g., between two buildings) is laid (Figures 5.3 e and f). This cable duct reinforcement must be bonded to the building reinforcement. Expansion joints in continuously reinforced cable ducts must be bridged analogously to the building expansion joints. Similarly, duct
Figure 5.3 e
Screening of underground cable routes by cages
Figure 5.3 f
(b)
Figure 5.3 f
(a)
Figure 5.3 f
(a, b) Practical execution of a cable duct with continuously interconnected reinforcement steel
Components and protective devices: construction, effect and application
141
connectors underneath or between adjacent buildings must be bridged. Also, with regard to cable ducts, it must be ensured that the maximum admissible voltage loadings on the cables laid or on the connected equipment will not be exceeded. Even so, depending on the assumed partial lightning current on the cable duct and on the cross section of the cable duct and, thus, on the number of longitudinal reinforcement rods, there may still arise voltage gradients from some 10 V to over 100 V per metre length of the cable duct.
Sources HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach, 1994) KERN, A.: ‘Blitz-Störschutz als Massnahme der EMV am Beispiel einer ausgedehnten Industrieanlage. 2. Forum für Sachverständige (Dehn u. Söhne, Nürnberg, Nov. 1995)
5.4 Shields for cables in buildings Cables shall be run near the equipotential bonding lines. These are parts of the steel construction, reinforced walls, cable supporting structures, cable trays or other electrically conductive parts which are connected to the equipotential bonding system at least at both ends. In principle, shielded cables should be used (Figure 5.4 a). This applies for electronic or data cables as well as for higher voltage levels. Pair-twisted signal
Figure 5.4 a
Connection of cable screens to a local equipotential bonding bar
142
Overvoltage protection of low voltage systems
cables are to be preferred. For related lines of one signalling circuit a twisted pair each is to be used, so that the incoupled transverse voltage on cable runs must be neglected. The limitation of the incoupled series voltage determines the protection measures. To lessen surges by overcoupling, power and signalling cables must be consequently separated, if possible by using cable supporting structures which are included in the equipotential bonding (Figures 5.4 b and c). Different separations are needed depending on the cable parallel running length. Thus:
Figure 5.4 b
Cable support constructions
Figure 5.4 c
Line screen out of continuous metal cable racks and metal coverings with pipe bends removed (Source: H. Neuhaus)
Components and protective devices: construction, effect and application for l < 5 m for 5 m < l < 20 m for l > 20 m
143
distance at random distance > 10 cm distance > 20 cm.
Also in existing systems it may become necessary to shield the cable routes (subsequently). For this purpose a retrofit set is shown in Figures 5.4 d (a and b), consisting of shielded sleevings (yard goods) provided with a closing system in the longitudinal direction. Tests for this set have demonstrated a shield damping of about 50 dB.
Sources HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept’ (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach, 1994) KERN, A.: ‘Blitz-Störschutz als Massnahme der EMV am Beispiel einer ausgedehnten Industrieanlage’ 2. Forum für Sachverständige. (Dehn u. Söhne, Nürnberg, Nov. 1995) BROCKE, R., FRENTZEL, R., and ZAHLMANN, P.: ‘Schirmung von Kabeltrassen gegen Blitzeinkopplungen.’ etz 1996, No. 20
5.5 Optoelectronic connections In systems of great transmission bandwidth and extra sensitive electronic components, apart from the specific use of surge protection devices, circuit parts or component conductor systems will be opened by the insertion of optoelectronic coupling gaps (Figure 5.5 a). Before detailing the application possibilities and limitations of optoelectronic components from the viewpoint of surge protection, these components and devices will be introduced separately as follows.
Figure 5.4 d
(a)
Figure 5.4 d
(b)
Figure 5.4 d
EMC-retrofit assembly for cable screening: (a) Components of screening tube (yard goods) bonding set and terminal clamps (b) Two samples bonded
144
Overvoltage protection of low voltage systems
Figure 5.5 a
Subdivision into component conductor systems
5.5.1 Optical fibre transmission system An optoelectronic connection consists of a transmitter, optical fibre and receiver. The transmitter converts an electrical signal into an optical signal which is then transmitted to a receiver by an optical fibre. The optical signal is then converted back to an electrical signal in the receiver. Lightemitting diodes (LEDs) or laser diodes are used in the transmitters. The optical fibre conductors are usually made of glass fibre although plastic fibres are sometimes used. Individual fibres have diameters ranging between 100 and 150 μm. A single complete conductor can comprise between 10 and 100 fibres. Photodiodes, phototransistors, photothyristors or other photoelectronic devices are used in the receivers. Figure 5.5.1 a shows the principle of an optoelectronic system for data transmission over long distances. Optical fibre transmission systems have the following advantages over traditional conductor systems: there is no crosstalk between two lines; they have high transmission capacities in a system of low mass; and they are very space-efficient in the installation. If the optical fibre is of pure glass, there are further advantages with regard to surge protection: namely, optimal electrical insulation between transmitter and receiver, and insensitivity to incouplings. However, it must be taken into account that optical fibre cables often have a metal sheath for damage protection which can be heated by lightning to such a degree that the cable will be damaged. The components introduced so far are used for the construction of optical fibre systems for data transmission over long distances. If, however, a potential separation of elements of an electronic system is required, then optocouplers are used.
Components and protective devices: construction, effect and application
Figure 5.5.1 a
145
Fibre-optic transmission system: basic circuit diagram (Source: Siemens)
5.5.2 Optocoupler The optocoupler is a combination of radiation emitting (input) and radiation sensitive (output) components. Light transmission between these two components takes place across a thin layer of optical medium which simultaneously isolates the input from the output (Figure 5.5.2 a). Optocouplers are available having a voltage withstand of some 100 V to 10 kV between input and output. However, this voltage only indicates the insulation strength between input and output. Semiconductor components with known surge sensitivity are connected between the terminals of the optocoupler; this means that special attention must be paid to a sufficient limitation of differential-mode overvoltages when using them in transmission systems. Furthermore, these semiconductor components, namely the diode and the phototransistor, can be thermally destroyed by low, long-duration overvoltages and this may reduce the voltage strength of the insulation gap between input and output. Optocouplers are used as optoelectronic coupling elements for signal transmission in cases where galvanic separation is required in sensitive system elements (Figure 5.5.2 b). Their function is thus comparable with that of transmitters being primarily used for blocking low common-mode voltages. They cannot, however, be used for protection against voltages higher than their transmitter/receiver surge withstand capability. Most optoelectronic systems are supplied with mains current. There is, therefore, another galvanic coupling through the mains supply which also is susceptible to the danger of entering overvoltages. Surge protection devices should thus be incorporated.
Source TRAPP, N.: ‘Die Optimierung des Inneren Blitzschutzes durch den Einsatz optoelektronischer Baugruppen’. 16. Internationale Blitschutzkonferenz, Szeged, 1981, Beitrag R-5.04
5.6 Equipotential bonding Lightning protection equipotential bonding of a ‘volume to protect’ includes all incoming metal installations as explained in Section
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Overvoltage protection of low voltage systems
Figure 5.5.2 a
Optocoupler: Function diagram
Figure 5.5.2 b
Connection of input and output lines to a data processing system by optocoupler
4.1.3.1.4. Figure 5.6 a shows an equipotential bonding bar which is used for the main equipotential bonding according to DIN VDE 0100 Parts 410 and 540, as well as for lightning protection equipotential bonding according to DIN VDE 0185. In the case of extended telecommunication systems, a duly shaped lightning protection equipotential bonding bar (installed at ground level inside the building) also functions as an ‘earth bus’ and is usually installed as an ‘earth ring bus’ inside the building (DIN VDE 0800 Part 2). The ‘earth ring bus’, a ring equipotential bonding bar, is a copper bar having a minimum cross section of 50 mm2 for surface mounting at a
Components and protective devices: construction, effect and application
Figure 5.6 a
147
Equipotential bonding bar (acc. to DIN VDE 0618) with snap-on terminals for conductor cross sections 25 to 95 mm2
distance of some centimetres from the wall. At distances of about 5 m it should be bonded to the foundation earth electrode (DIN VDE 0800 Part 2) (Figures 4.1.3.1.4 a and 5.2 j). This bonding can also be realized over the reinforcement. An equipotential bonding bar such as that in Figure 5.6 a can be sufficient for small local systems. If the discharge system consists of plain metal components which constitute an effective electromagnetic shield (Figure 5.6 b), the equipotential bonding bars can be directly bonded with the shield. A lowimpedance coupling of the external conductors and their shields is required for lightning protection equipotential bonding at the interface between lightning protection zones 0 and 1. Equipotential bonding is, therefore, often carried out using a bonding plate with multiple radial or even coaxial connections of the conduits or line shields (Figure 5.6 c). Equipotential bonding is not only for the protection of electronic systems but it must also fulfil special functions. A low-impedance equipotential bonding system, that is, an entity formed of interconnected equipotential bonding lines including the metal parts of the electric systems (such as enclosures, racks, cable trays etc. Figures 5.6 b, 5.2 o, 5.4 b) and the building (e.g., reinforcement in floors, walls and ceilings, supporting structures between floors) is possible using a meshed, plane or space-covering formation. Such a meshed overall building equipotential bonding system is the best way to reduce overvoltages in telecommunication systems and is the basis for the coordinated use of arresters (surge protection devices, filters etc.). Different types of functional equipotential bonding systems as needed for telecommunication facilities and systems, are described in section
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Overvoltage protection of low voltage systems
Figure 5.6 b
Connection of air terminations, equipotential bonding, earthing and installation to the reinforcement (Source: Frentzel, R., TÜV South Germany)
Figure 5.6 c
Connection of piping entries to the reinforcement (Source: Frentzel, R., TÜV South Germany)
4.1.3.1.4. Metal supports, cabinets, enclosures, cable racks etc. in rooms with telecommunication facilities and systems must be included in the meshed functional equipotential bonding, as Figures 5.6 b, 5.2 o, 5.4 b and 5.6 d show. Another possibility for achieving functional equipotential bonding is to create an equipotential bonding network by means of the metal supporting structures between floors. It is useful to install a local ring equipotential bonding bar, as shown in Figure 5.2. j, which then is connected to the ‘earth ring bus’ several times (also over the steel reinforcement or the protection zone screen) (Figure 5.6 e).
Components and protective devices: construction, effect and application
Figure 5.6 d
Wall bushing of cable racks in meshed functional equipotential bonding
Figure 5.6 e
Equipotential bonding bar for communication technology room
149
Above all else, functional equipotential bonding shall include: enclosures and racks of the telecommunication systems • metal conductors electrical systems which do not carry operational volt• ages and/or ofcurrents. In the latter case, these include: (i) the protective conductors (PE) of the power system, (ii) the earth electrode conductors of the telecommunication system, (iii) the outer shields of the telecommunication cables, and if necessary, the chassis terminals of the electronic devices and systems.
Sources HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach, 1994) DIN VDE 0800 Teil 2: ‘Fernmeldetechnik. Erdung und Potentialausgleich’ (VDE Verlag, GmbH, Berlin/Offenbach, July 1985)
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Overvoltage protection of low voltage systems
5.7 Isolating spark gaps Enclosed spark gaps which can carry test currents of 10/350 μs (Section 4.5.2 b) without being destroyed are known as isolating spark gaps. Up to their sparkover voltage, these spark gaps provide the electrical separation of two metal installations. Once the nominal spark-over point is reached, they create an electrical bonding path for the lightning current. This coupling is reset after the decay of the lightning current. Isolating spark gaps (Figure 5.7 a) are used at clearances between the lightning protection system and other earthed system parts in order to avoid uncontrolled arcing or puncturing at these points. They are used to incorporate metal installations, for example, into the lightning protection equipotential bonding system in cases where these installations cannot be interconnected due to corrosion effects (Figure 5.7 b). High specifications must be fulfilled for explosion-protected isolating spark gaps (Figure 5. 7 c). These are used to avoid open sparking in the event of a lightning strike in hazardous areas, for example, for bridging the insulation flanges in pipelines. The lightning impulse sparkover voltage 1.2/50 of such spark gaps should be not higher than 50% of the 50 Hz sparkover AC voltage (effective value) of the insulating flange to be protected. The impulse sparkover voltage of a spark gap depends on the rate of rise of the generated overvoltage wave. The steeper the wave, the shorter the time during which failure can occur. This voltage–time relationship is clearly shown by the impulse characteristic. Figure 5.7 d shows the impulse characteristic of the explosionprotected spark gap in Figure 5.7 e. It is extremely flat: hence, the spark gap limits rapidly rising overvoltage impulses to almost constant values of about 2 kV. ‘Sparkover voltage’ is not the only relevant factor in the design of a parallel-connected isolating spark gap. After the tripping of the isolating spark gap, a voltage with peak value û = L(di/dt)max is generated at the insulating part. L is the loop inductance and di/dt the rate of rise of current (Figure 5.7 e). From an equation supplied in the ‘Handbuch für Blitzschutz und Erdung’, the maximum value of inductance may be calculated for a square loop of length 300 mm, and a rope cross section of 25 mm2 Cu (r = 2.8 mm). This is L = 0.16 μH. After a direct strike the lightning current flows to both sides of a pipeline and a maximum rate-of-rise of current of (di/dt)max = 40 kA/μs can be assumed. For an impulse wave of 4/10 μs, this corresponds to a peak value of 120 kA. From the above data, the peak value of the voltage û = 6.4 kV for a loop length of 300 mm, and isolating spark gap elements with an
Components and protective devices: construction, effect and application
Figure 5.7 a spark gap
Isolating
Figure 5.7 c
Explosion-protected isolating spark gap
151
Figure 5.7 b Isolating spark gap for isolating metal systems of different potentials
effective sparkover voltage of more than 5 kV (i.e., peak value û = 5 kV √2 ≈7 kV) can be connected in parallel without any further testing. Maximum requirements are for isolating spark gaps. At the instant of the lightning strike, the gaps should be capable of carrying the lightning current through a protective insulation and afterwards retain the full insulating strength (cf. Sections 6.4 and 6.5). High-current spark gaps of this nature, type HSFS (Figure 5.7 f ), must therefore be capable of
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Overvoltage protection of low voltage systems
Figure 5.7 d
Impulse voltage–time curve of the explosion-protected isolating spark gap (Figure 5.7 c)
Figure 5.7 e
Voltage drop û caused by (di/dt)max
conducting especially high lightning currents without being destroyed and, during normal operation, they must offer the same high reliability as normal insulation components. This spark gap type HSFS has been proven in military applications and is in compliance with the requirements and tests of VDE specifications and DIN VDE 0800 Part 9. Figure 5.7 g shows such a high-
Components and protective devices: construction, effect and application
Figure 5.7 f type HSFS
High-current spark gap,
153
Figure 5.7 g High-current spark gap, type HSFS tested by laboratory simulated lightning current
efficiency spark gap under test conditions with a laboratory simulated lightning current. The unit blows the arc through special openings during discharge of the surge currents. This type of spark gap is housed in an enclosure which is equipped with baffle plates (Sections 6.4 and 6.5).
Sources HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatz elektronischer Geräte auch bei direkten Blitzeinschlägen. (Verlag TÜV Rheinland, Köln, 3. aktualisierte Auflage, 1993) HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach, 1994) DIN VDE 0800 Teil 9: ‘Fernmeldetechnik. KU-Werte sicherheitsbezogener Bauelemente und Isolierungen’ (VDE Verlag, GmbH, Berlin/Offenbach, May 1989)
5.8 Arresters According to their ranges of application, surge protective devices (SPDs) for power engineering and for information technology can be subdivided into two kinds: namely, lightning current arresters and surge arresters (cf. Section 4.5.2.1 and 4.5.2.2). SPDs are internationally standardized in IEC 61643-1:1998-02 ‘Surge protective devices connected to low-voltage power distribution systems. Part 1: Performance requirements and testing methods’. In this standard the SPDs are distinguished according to test classes (I, II, III). It is
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Overvoltage protection of low voltage systems
somewhat difficult for the user to understand this classification because it is primarily meant for the producer of the SPDs. A rather user-convenient SPD standardization is included in the German DIN VDE 0675 Part 6/6A1 and 6A2 (Table 5.8 a). As the requirements and tests of the German standard are more severe than the international standards, the German standard is taken as a basis for arrester classification. Lightning current arresters must be able to discharge (high energy) lightning currents or considerable parts of them non-destructively. They are dimensioned and tested in accordance with IEC 61643-1/E DIN VDE 0675 Part 6 and Part 6/A1 (Figure 5.8 a). Surge arresters only serve limiting overvoltages at relatively low-energy surge currents. Table 5.8 a E DIN VDE 0675 Part 6/A1
IEC 37A/447/CDV
Arresters class B, for lightning protection equipotential bonding purposes according to DIN VDE 0185 Part 1
Arrester: ‘Class I’
Arresters class C, for surge protection purposes in the permanent installation, especially for use in surge withstand category (surge category) III
Arrester: ‘Class II’
Arresters class D, for surge protection purposes in the mobile/permanent installation, especially for use in surge withstand category (surge category) II
Arrester: ‘Class III’
Figure 5.8 a
1 Test current impulse (10/350 μs) for lightning current 䊊 2 Test current impulse (8/20 μs) for surge arresters; 䊊 arresters according to E DIN VDE 0675 Part 6/A1
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155
5.8.1 Arresters for power engineering As explained in chapter 4.5.2, arresters for systems and equipment in power engineering are subdivided into requirement classes A, B, C and D according to IEC 61643-1/E DIN VDE 0675 Part 6 and Part 6 A1 (Figure 5.8.1 a and Tables 5.8.1 a and b). Class A arresters are used in low-voltage overhead lines. Class B, C and D arresters are used in permanent building installations. The highest requirements for discharge capability are for class B arresters. These are lightning current arresters used in the scope of lightning- and surgeprotection at the interface of lightning protection zones 0A/1. Such arresters must be able to carry lightning partial currents with wave shape 10/350 μs non-destructively for several strikes. The task of these lightning current arresters is to prevent destructive lightning partial currents from penetrating the electrical system of a building. According to the latest ‘Technical Supply Conditions’ of German power supply companies, lightning current arresters may also be installed before the meter. Surge arresters are installed (at the boundary of lightning protection zones 1/2) for protection against surges arising between the active conductors L1, L2, L3 and N as against the protective conductor PE. These are class C surge arresters with a discharge capacity of some 10 kA (8/20 μs). The final link in lightning and surge protection for power engineering systems is the terminal protection (boundary of lightning protection zones 2/3). The main task of the class D arresters used is to protect against surges arising between L and N. These are mainly switching overvoltages. 5.8.1.1 Surge arresters for low-voltage overhead lines, class A Surge arresters for use in low-voltage overhead lines (Figure 5.8.1.1 a) are usually constructed as a series connection of spark gap and voltagedependent resistor (Figure 5.8.1.1 b) designed for a nominal discharge surge current of 8/20 μs with 5 kA peak value (Table 5.8.1.1 a). Such a loading occurs in cases of remote lightning striking into the power supply system. In the case of a direct lightning strike the spark gap welds and the non-linear resistor fuses. A disconnector separates the defective arrester from the system (e.g., indicated by a detached indicator sleeve). Figure 5.8.1.1 c indicates the voltage UM arising between overhead line and ‘earth’ on discharging a 5 kA (8/20) surge current. UM is composed of: protection level U (about 2 kV) • the the drop at the earth conductor inductance (at a 5 kA 8/20 • surgevoltage current, (di/dt) is about 1 kA/μs, therefore the voltage drop P
max
•
peak value is about 10 kV) the voltage drop at the impulse earth resistance RE (peak value about 50 kV).
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Overvoltage protection of low voltage systems
Figure 5.8.1 a
Table 5.8.1 a
Application of arresters in a power technical network
Requirement classes of arresters for power technical systems in accordance with E DIN VDE 00675 Part 6 and E DIN VDE 0675 Part 6/A1
The total of these (time-related) potential gradients results in the curve UM = f (t) in Figure 5.8.1.1 c, b, with a peak value UM of about 55 kV. Hence, these arresters, when used in low-voltage overhead lines, cannot effectively protect the connected consumer installations (Figure 5.8.1.1 c, a) in discharging the nominal discharge surge current. Primarily, they protect the low voltage overhead line systems themselves.
Components and protective devices: construction, effect and application Table 5.8.1 b
157
Assignment of the arrester gear
Figure 5.8.1.1 a Arrester hooked into the overhead line (Source: Siemens)
Figure 5.8.1.1 b Structure of the arrester in Figure 5.8.1.1 a: (1) fusible point, (2) fusible strip, (3) indicating sleeve, (4) nonlinear resistor disc (silicon carbide), (5) spark gap (Source: Siemens)
5.8.1.2 Lightning current arresters for lightning protection equipotential bonding, class B Lightning current arresters have to meet the requirements in Table 5.8.1.2 a. There may be a (computer based) calculation of the required lightning current-carrying capability according to the respective installation factors. According to IEC 61312-1:1995-02: ‘Protection against lightning electromagnetic impulse. Part 1: General principles’ the distribution shown in Figure 5.8.1.2 a may be assumed concerning the distribution of
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Overvoltage protection of low voltage systems
Table 5.8.1.1 a
Arresters – class A
the lightning and lightning partial currents at a lightning strike into the air-termination system. The lightning current arrester loading can be estimated as follows. A lightning current of 200 kA (10/350 μs) is the maximum loading for protection level I (according to Table 5.8.1.2 b). According to Figure 5.8.1.2 a this lightning current is distributed as follows: (a) 50% (100 kA, 10/350 μs) is discharged through the earthing system, and (b) 50% (100 kA, 10/350 μs) is discharged by the connected supply systems (power system, information technical system, metal piping etc.). If, in the worst case, there is only the power system, it will be loaded by 50% of lightning current. Considering the worst case of only two conductors (L and PEN), there will be a loading of 50 kA (10/350 μs) each per conductor. For this worst case scenario the loading of a onepole lightning current arrester will have the following parameters: a peak value 50 kA (10/350 μs), a charge of 25 As and a specific energy of 0.625 MJ/Ω. Lightning current arresters for such high demands are mostly airgliding spark gap structures which are able to extinguish the flowing mains follow-current automatically after having been activated (Figure 5.8.1.2 b). Such leakage current-free gliding spark gaps are often a construction of rotationally symmetric electrodes with a spacing insulating layer which has an arc-exhausting effect. Their ‘breakwater function’ is a major advantage of such spark gap arresters. Wave shape 10/350 μs lightning currents are shortened to surge currents of wave shape < 8/20 μs which are compatible for downstream installed surge arresters. Figure 5.8.1.2 c shows four such practice-proven lightning current arresters. The DEHNport® lightning current arrester (Figure 5.8.1.2 d) is equipped with a capacitively-controlled tandem gliding spark gap. It consists of three rotationally symmetric electrodes with spacers made out of different insulating materials. Thus, a high discharge capacity of 75 kA (10/350 μs) at a low protection level of 3.5 kV (1.2/50 μs) is achieved. This arrester exhausts hot gases when discharging lightning currents. Therefore other bare, live metal parts must be kept in minimum distances as shown in Figure 5.8.1.2 e.
Components and protective devices: construction, effect and application
Figure 5.8.1.1 c
(a)
Figure 5.8.1.1 c
(b)
Figure 5.8.1.1 c
Protective effect of arresters installed at overhead lines (a) Spatial arrangement (b) Voltages at discharging a 5 kA (8/20 μs) impulse current
159
Usual types of lightning current arrester based on spark gaps are able to extinguish mains follow-currents of up to 4 kAeff (50 Hz) automatically. The spark gap in the lightning current arrester must establish a ‘counter voltage’ (arc voltage) in the range of the supplying system voltage in order to obtain a better follow-current extinguishing capability. Therefore, a completely new function principle had to be developed for the required follow-current-limiting spark gap. This is based on optimized arc cooling by radial and axial blowing. The necessary cooling gas is
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Overvoltage protection of low voltage systems
Table 5.8.1.2 a
Arresters – class B
Table 5.8.1.2 b
Lightning current parameters acc. to IEC 61024-1 resp. IEC 61312-1 (ENV 61024-1)
Figure 5.8.1.2 a
Assumed distribution of the lightning current
Components and protective devices: construction, effect and application
Figure 5.8.1.2 b
161
Behaviour of a lightning current arrester based on a spark gap
generated under the influence of the arc by the surrounding plastic material. Owing to the forced blowing, the arc voltage will be increased. Figure 5.8.1.2 f shows the principle of a radially and axially blown arc (RADAX-flow technology). The cooling gas released under the influence of arc streams radially (from all sides) towards the arc and ‘compresses’ it. Owing to the reduced cross section of the arc pillar, the arc resistance will rise and the arc voltage increase. The gas heated by the influence of the arc is finally exhausted by an axial gas streaming through an expulsion nozzle. For RADAX-flow spark gap technology, the follow-current (let-through current) actually flowing through the arrester will be limited to a very low value, independent of the possible mains short-circuit current (section 5.8.1.6.3). The use of RADAX-flow technology in series bays of usual dimensions (Figure 5.8.1.2 g) has led to a completely new generation of lightning current arresters combining a high surge current discharge capability with the breaking performance of a circuit breaker: The problem of false tripping of fuses due to mains follow-currents is solved. Because of these excellent operating characteristics, lightning current arresters in RADAX-flow technology are especially suitable for installation in the sealed part of a consumer system (mains distribution system). DEHNbloc® and DEHNbloc® NH contain a pressure-controlled encapsulated gliding spark gap (Figure 5.8.1.2 h, a). The encapsulation of the spark gaps prevents the ‘blowing’ of these lightning current arresters. Thus, the spacing problem (safety distances) is solved (Figure 5.8.1.2 h, d). The discharge capacity of these encapsulated gliding spark gaps is about 25 kA (10/350 μs) and the protection level is lower than 4 kV (1,2/ 50 μs). Owing to the pressure-controlled arc quenching, the mains followcurrent will be safely controlled. The leakage-current-free encapsulated gliding spark gap is embedded into a special insulating material with arcquenching characteristic. The pressure arising at the activation of the spark gaps enforces the quenching effect of the insulating material.
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Overvoltage protection of low voltage systems
Figure 5.8.1.2 c
(a)
Figure 5.8.1.2 c
(b)
Figure 5.8.1.2 c
(c)
Figure 5.8.1.2 c
Lightning current arrester (from left to right): (a) DEHNport ®, (b) DEHNport ® Maxi, (c) DEHNbloc ®, (three-pole design), (d) DEHNbloc ® NH
Figure 5.8.1.2 c
(d)
Components and protective devices: construction, effect and application
Figure 5.8.1.2 d (a) DEHNport® with tandem gliding spark gap
Figure 5.8.1.2 e
Figure 5.8.1.2 d (b) Sectional model tandem gliding spark gap
163
Figure 5.8.1.2 d (c) Function principle
Lightning current arrester type DEHNport ®, installed at the input of a power supply line from lightning protection zone 0 into lightning protection zone 1
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Overvoltage protection of low voltage systems
Figure 5.8.1.2 f
Basic circuit diagram for an arc blown out radially and axially in RADAX-flow technology
Figure 5.8.1.2 g
Lightning current arrester DEHNport with RADAX-flow technology in the mains connection box for application in the area before the meter
Components and protective devices: construction, effect and application
Figure 5.8.1.2.h
165
(b) DEHNbloc ®
Figure 5.8.1.2 h (a) Encapsulated gliding spark gap
Figure 5.8.1.2 h (c) DEHNbloc® NH
Figure 5.8.1.2.h distances
(d) Installation without minimum
The DEHNbloc® (Figure 5.8.1.2 h, b) is a compact, three-pole arrester unit (with a space-saving width of only four modules). It is especially suitable for the common TN-C system. Also the multifunction terminals for the clamping of both terminal wires and comb-type bars are easy to use (comparable to the DEHNport®). The DEHNbloc® NH (Figure 5.8.1.2 h, c) is the first lightning current arrester for mounting on
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Overvoltage protection of low voltage systems
NH-fuse bases size 00 (also in fuse-disconnector blocks). Installation by a usual fuse handle is possible without operational interruption. This is especially attractive for application in industrial plants. Because of the gliding spark gap technology the ‘breakwater function’ is guaranteed and thus an energetic coordination (as explained in chapter 4.5.4) with surge arresters based on varistor technology, like DEHNguard®, is possible. DEHNport®, DEHNport® Maxi, DEHNbloc® NH and DEHNbloc® can be installed upstream of the meter because of the leakage current-free operation and the high insulation resistance. Another special lightning current arrester (according to E DIN VDE 0675 Part 6/A2) based on air spark gaps is the N-PE lightning current arrester DEHNgap B (Figure 5.8.1.2 i). What is the task of an N-PE lightning current arrester? Lightning current arresters should be installed as close as possible to the building input. In the TT-system this means an installation upstream of the residual-current device. In the case of an earth fault in this range, the upstream fuse must disconnect. But this is not guaranteed under unfavourable earthing conditions. On using the N–PE lightning current arrester DEHNgap B in a ‘3 + 1-circuit’, where the three phases (L1, L2, L3) are connected to gliding spark gaps (e.g., the DEHNport) and a spark gap is installed between neutral conductor N and protective conductor PE (chapter 5.8.1.6), there is a short-circuit current between the phases and neutral conductor in the case of an arrester fault which the upstream fuse can now break in the time provided. The N–PE lightning current arrester type DEHNgap B can safely conduct the residual current of the incoupled lightning between the earthing system and the neutral conductor up to 100 kA (10/350 μs) at a sparkover voltage < 4 kV (1.2/50 μs). The compact enclosure design with a space of two modules and the multifunction terminals for clamping both the terminal wires and combtype bars makes the N–PE lightning current arrester DEHNgap B very easy to use. Also a quench gap (Figure 5.8.1.2 j) is suitable for the inclusion of power lines into the lightning protection equipotential bonding at the interface of lightning protection zones 0 and 1. It is also able to extinguish mains follow-currents automatically. This lightning current arrester has been proven in practice for years and is included in the standards DIN VDE 0804 Part 2 and DIN VDE 0845 Part 1. Quench gaps are, for example, used in the lightning current arrester arrangement described in chapter 6.5 (Figures 6.5 b and 6.5 c) to protect transportable telecommunication facilities and for the connection of the mains supply of TV transmitters (chapter 6.4, Figures 6.4 e and 6.4 f, b).
Components and protective devices: construction, effect and application
Figure 5.8.1.2 i
DEHNgap B
Figure 5.8.1.2 j
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Quench gap
5.8.1.3 Surge arresters for protection of permanent installation, class C According to DIN VDE 0675 Part 6, class C surge arresters are used in the permanent building installation. At lightning protection zone interfaces 0B/1 and higher, the phases (L1, L2, L3) of the mains are equipped with surge arresters. In TT and TN–S systems, where the N conductor is run separately from the PE conductor, the N conductor also has an arrester. Valve-type arresters are constructed according to DIN VDE 0675 Parts 1 and 6 or IEC 99.1 and consist of a spark gap and voltagedependent resistor connected in series; their nominal discharge surge current is 5 kA (8/20 μs); the voltage arising at the consumer installation is about 1.5 kV. Figures 5.8.1.3 a and b show valve-type arresters containing one airspark-gap and one silicon carbide resistor. Voltage and current characteristics for voltage limitation are shown in Figure 5.8.1.3 c. Valve-type arresters are characterized by their quenching voltage Ul (continuous operating voltage Uc according to DIN VDE 0675 Part 6), at which an arrester (in an operating duty test) is still able to extinguish the mains follow-current automatically. Figure 5.8.1.3 d shows the voltage and current during such an operating duty test according to DIN VDE 0675 Part 1 at a valve-type arrester for Ul = 280 V, whereas Figure 5.8.1.3 e shows the protection characteristic of this arrester. If the valve-type arrester shown in Figure 5.8.1.3 a is overloaded, the integrated disconnector separates the defective arrester from the mains. Downstream consumer installations will stay alive. However, such defective arresters must be replaced as they no longer protect against surges.
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Overvoltage protection of low voltage systems
Figure 5.8.1.3 a
Nonlinear resistor type gapped surge arrester
Figure 5.8.1.3 b
Nonlinear resistor type gapped surge arrester (acc. to Figure 5.8.1.3 a), installed in a low-voltage distribution system
Valve-type arresters have indicators to show the defective and disconnected state (Figure 5.8.1.3 f). Figure 5.8.1.3 g shows an arrester for NH fuse bases size 00 (connected to L and PE). Figure 5.8.1.3 h shows a practical example. Replacement of an arrester in a live state is easy by means of an NH fuse handle. If holders with a microswitch (Figure 5.8.1.3 i) are used, the projecting pin of
Components and protective devices: construction, effect and application
169
Figure 5.8.1.3 c
Performance of a nonlinear resistor type gapped surge arrester (series connection of spark gap and silicon carbide varistor)
Figure 5.8.1.3 d
Performance of a nonlinear resistor type gapped surge arrester (acc. to Figure 5.8.1.3 a) during the operating duty test
Figure 5.8.1.3 e
Protective characteristic of a nonlinear resistor type gapped surge arrester (acc. to Figure 8.1.3 a)
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Overvoltage protection of low voltage systems
Figure 5.8.1.3 f Nonlinear resistor type Figure 5.8.1.3 g Surge arrester in gapped surge arrester with disconnector NH type of construction and indicator (acc. to Figure 8.1.3 a). Arrester on the right is defective, disconnector has operated (pushed up button)
Figure 5.8.1.3 h
Surge arrester (acc. to Figure 5.8.1.3 g), installed in a distribution system
the disconnected arrester will press this switch and a remote indication of the necessary arrester replacement becomes possible. Recent surge arrester models have zinc oxide varistors (Figure 5.8.1.3 j) where almost no mains follow-current arises; these can be used without a series connected spark gap. Figure 5.8.1.3 k shows such a surge arrester in a modular design with a thermally controlled zinc oxide varistor for space-saving installation in distribution systems (Figure 5.8.1.3 l). The basic overvoltage limiting behaviour is shown in Figure 5.8.1.3 m;
Components and protective devices: construction, effect and application
Figure 5.8.1.3 j
Metal oxide varistor
Figure 5.8.1.3 i Remote indication of the operation of the arrester disconnector (acc. to Figure 5.8.1.3 g) by microswitch
Figure 5.8.1.3 k
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Surge arrester in modular design, type DEHNguard®®
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Overvoltage protection of low voltage systems
Figure 5.8.1.3 l
Figure 5.8.1.3 m
Surge arrester DEHNguard® installed at the input of a power supply line from lightning protection zone 1 to lightning protection zone 2
Performance of a surge arrester based on metal oxide (acc. to Figure 5.8.1.3 k)
the limiting voltage is exclusively determined by the residual voltage at the discharge of the impulse current. A live surge arrester on a metal oxide basis (without spark gaps) carries the current corresponding to its U/I characteristic (Figure 5.8.1.3 n). Such arresters are always ‘in operation’, whereas an arrester based on a spark gap needs ‘activation’ by an overvoltage. Usual surge arresters based on ZnO have a discharge capability of
Components and protective devices: construction, effect and application
Figure 5.8.1.3 n
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U/I characteristic of a varistor
15 kA (8/20 μs). The protection element must be able to conduct this discharge current safely and without changing the characteristic at least 20 times. This is sufficient to prevent overloading in the case of a ‘creep under’ of a backup lightning current arrester and correctly dimensioned decoupling impedance (chapter 5.8.1.5). If for example, owing to unfavourable conditions, there is a missing backup lightning current arrester (in spark gap technology), this discharge capacity is exceeded and thus the varistor overloaded, then it will be automatically disconnected from the mains. This prevents a defective arrester from disturbing the operation. Remote control is possible by a local indicator and a potential-free changeover contact. DEHNguard® T (Figure 5.8.1.3 o) consists of two parts: a base and an attachable varistor module which can be replaced in case of overloading. For insulation measurements of the system, quick removal is advantageous. To avoid errors, the base and varistor module are provided with code pins according to their nominal voltage. Figure 5.8.3.1 p shows a surge arrester with degree of protection IP × 4W. This is particularly suitable for industrial applications (to be plugged into NH fuse holders, size 00) and has (like the arrester shown in Figure 5.8.1.3 g) an integrated backup fuse which does not need any further backup fuse on the mains (section 5.8.1.5). The 3 + 1 circuit (chapter 5.8.1.5) allows the application of surge arresters upstream of the residual current device. The three phase conductors (L1, L2, L3) are connected to varistors towards the neutral conductor N, and the surge arrester DEHNgap C (Figure 5.8.1.3 q), based on a spark gap having a sparkover voltage of about 1.5 kV (1.2/50), is
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Overvoltage protection of low voltage systems
Figure 5.8.1.3 o Surge arrester DEHNguard® T
Figure 5.8.1.3 p Surge arrester VNH 280
Figure 5.8.1.3 q Surge arrester DEHNguard® C
installed between neutral conductor N and protective conductor PE. Thus, the upstream fuse can meet the disconnection requirements in the case of a fault. The space-saving one modular design of the surge arresters DEHNguard® and DEHNgap C and the multifunction terminals for wires and usual comb-type bars make them especially easy to install. 5.8.1.4 Surge arresters for application at socket outlets, class D Surge arresters for mobile application at socket outlets (overvoltage category II) are assigned to requirement class D according to E DIN VDE 0675 Part 6. Such pluggable protectors (Figure 5.8.1.4 a) are often equipped with additional filters (Figure 5.8.1.4 b). The SF protector has a visual function indicator (green lamp) and a visual fault indicator (red lamp). When overloading it is disconnected automatically from the mains without power interruption. The plug-in surge protection adapter shown in Figure 5.8.1.4 c is a combination of surge arrester and interference suppressor filter. Further types of surge arresters used in this range are shown in Figures 5.8.1.4 d to f: According to design and testing, these are class D protectors. The surge protection socket outlet (Figure 5.8.1.4 d) has a supervisory device and a disconnection device with a green lamp as visual function indication and a red lamp as fault indication (indication of the disconnected mains). The surge arrester NM-DK 280 (Figure 5.8.1.4 e) is suitable for application in cable ducts and flush-mounted boxes. Because of its feed-through terminals it can be easily inserted into circuits. It is adaptable to all types of switches as it can be covered by the central disc according to DIN 43 696. The protector shown in Figure 5.8.1.4 f is for power supply protection of industrial electronics equipment (e.g., programmable controllers, SPC) against surges and high-frequency disturbance voltages.
Components and protective devices: construction, effect and application
Figure 5.8.1.4 a Pluggable surge arrester protects mains input of a computer
Figure 5.8.1.4 c
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Figure 5.8.1.4 b SF-protector (surge arrester with filter) for protection against transient surges and frequent interference voltages
SFL-protector: Multiple socket outlet with surge arrester and filter
5.8.1.5 Surge arresters for application at equipment inputs Equipment with a power technical input (which may form its own lightning protection zone) can be directly protected at this input by surge arresters as mini-modules (Figure 5.8.1.5 a) and (Figure 5.8.1.5 b). They protect electronic equipment of overvoltage category I. These arresters are designed and tested according to E DIN VDE 0675 Part 6 as class D. 5.8.1.6 Application of lightning current arresters and surge arresters Planning and execution of surge protection measures in the scope of an EMC-compliant protection strategy must lead to a coordinated
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Overvoltage protection of low voltage systems
Figure 5.8.1.4 d Socket outlet (with earthing contact) with overvoltage protection
Figure 5.8.1.4 f
Figure 5.8.1.4 e Surge protective device NM-DK 280 for cable ducts
SPS-protector: Surge protector with interference suppressor filter
protection system. A consequence of the often missing system consideration today is the uncoordinated installation of arresters at different points of the system which impair or even neutralize each other or have an inadmissible retroactive effect on the whole system. One of the first
Components and protective devices: construction, effect and application
Figure 5.8.1.5 a Surge protective mains module VC 280/2
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Figure 5.8.1.5 b Surge arrester (acc. to Figure 5.8.1.5 a) connected to power pack
essentials for the planning and execution of surge protection for a complex system is an organizing principle which subdivides the protected system into areas of graded demands. The EMC-oriented concept of lightning protection zones is such a principle. The concept of lightning protection zones allows the determination of the corresponding stress parameters for the individual arresters. The list of requirements for the arresters used can be basically subdivided into requirements for the individual arresters and requirements which are due to the system character of the total protection. The most important parameter for an individual arrester is its surge current-carrying capability. The demanded parameter value is due to the conditions of application of the arrester in the concept of lightning protection zones. For a lightning current arrester (at the boundary of LPZ 0A/1) these values are due to the primary lightning threat parameters (IEC 61312-1) and the real conditions of installation. For the design of the individual arresters the question of how many partial systems and conductors the total lightning current is distributed over must also be clarified (IEC 61312-1). Within lightning protection zone 1 there still remains the conducted residual parameters of the lightning current arrester as well as the overvoltages induced by the electromagnetic field of lightning and internal sources of interference (e.g., switching operations) as stress parameters for downstream protective equipment. The requirements for surge arresters that are installed at the boundary of lightning protection zone LPZ 1/2 must include this stressing. There are additional requirements for the different arresters as individual elements because of the system character of the whole protection system. It is necessary that the protection levels of the different arresters in the
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Overvoltage protection of low voltage systems
protection system be in accordance with the rules of insulation coordination of IEC 60664-1 (Figure 5.8.1.6 a). Coordination of the arresters between each other ensures that the individual protection devices are loaded as effectively as possible and maximum safety of the system is achieved. In addition to these specific requirements of surge protection there are demands for harmonization of surge protection–system protection, requiring coordination between the arresters’ parameters and the values of the conventional system protection devices (fuses, circuit breakers etc.). The special regulations which both the planner and installer (electrician) of the protective system must take into account are handled in the following notes. 5.8.1.6.1 Graded application of arresters, energy coordination between surge arresters and equipment to protect. The requirements for cascaded arresters in a protection system depend on the concept of protection zones. The planner is in charge of selecting the different coordinated arresters which must reduce step-by-step the incoming (lightning partial currents) or internally generated (switching surges) hazard to the withstand capability of the terminal units to be protected. To adapt a surge protection device (SPD, arrester) to the peripheral interface of a piece of equipment the interference immunity factor of the equipment and the maximum let-through parameters (output parameters) of the SPD must be known. This must be coordinated with the energy loadability of the equipment input. In addition to the arrester
Figure 5.8.1.6 a
Example for the application of lightning current arresters and surge arresters
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protection level the maximum values of the integral parameters of output voltage and output current are also of importance for energy coordination. Coordination, in this case, means to dimension a protective circuit upstream of an equipment interface in such a way that only at an imminent overloading of the device’s internal protective circuit will the upstream protective grade (SPD) become effective. The ‘operating behaviour’ of the upstream protective grade (SPD) and the loadability of the equipment’s protective circuit must overlap one another (i.e., form a common ‘interface’). Only thus is it possible to obtain a good balance between the costs for the protective circuit and the benefits which are achieved. The ‘conditions of adaptation’ described, however, are not only valid for the surge protective device and terminal unit but also for the use of arresters in a graded concept of protection zones (Figures 5.8.1.6.1 a). For a lightning current stressing arrangement according to 5.8.1.6 a and 5.8.1.6.1 a, the class C surge arrester in the subdistribution board will operate first due to its low protection level. According to its nominal discharge data this arrester has a protection level < 1.5 kV. This voltage is insufficient to operate the upstream class B lightning current arrester (as the operating value of this spark gap is between 3 and 3.5 kV). In order not to overload the class C surge arrester in the subdistribution board, there must be an additional series voltage drop on the line between the surge arrester and the lightning current arrester which, in sum with the
Figure 5.8.1.6.1 a
(a) Protective gear for power technical systems at the interfaces of lightning protection zones (LPZ)
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Overvoltage protection of low voltage systems
Figure 5.8.1.6.1
(b) Currents through surge arresters and lightning current arresters at lightning strikes
protection level of the class C surge arrester in the subdistribution, reaches the operating value of the spark gap in the class B lightning current arrester. In the 230/400 V mains this series voltage drop can be obtained by using the cable impedance, or by using a concentrated inductance (decoupling choke). The cable inductance depends on the routing of the protective conductor PE. If the protective conductor is in one cable with L1, L2, L3 and N (as for cable type NYM-J), a cable length of at least 15 m is the necessary decoupling length between the class B lightning current arrester and the class C surge arrester (Figure 5.8.1.6.1 b). If the protective conductor is separate from L1, L2, L3 and N (as for cable type NYM-O), and the distance between the protective conductor and cable is 1 m (as in Figure 5.8.1.6.1 c) the necessary minimum decoupling length is 5 m. If these cable lengths cannot be realized, the class B and class C arresters can be coordinated by decoupling chokes (Figure 5.8.1.6.1 d). With such decoupling chokes there is the possibility of installing the arresters in one place (Figure 5.8.1.6.1 e), and insecurities due to installation (such as the actual line length) can be avoided. Responsibility for this arrangement thus passes over from the installer to the producer of the protective devices who indicates the necessary induction value for the coordination of his arresters. For dimensioning the decoupling choke it is possible to choose the inductance value as low as possible by using all securities granted by the protective devices, or to increase the safety of the graded protective circuit by a higher minimum inductance value. Increasing the inductance value by several microhenry (μH) does not mean any restriction on normal operation. On the contrary, because of too strictly dimensioned
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Figure 5.8.1.6.1 b
Necessary decoupling line length for arresters of requirement classes B and C when protective conductor PE is in the cable
Figure 5.8.1.6.1 c
Necessary decoupling line length for arresters of requirement classes B and C when laying the protective conductor separately
Figure 5.8.1.6.1 d
Decoupling inductance DEHNbridge (15 μH) for the energy coordination of lightning current arresters (DEHNbloc®, DEHNport®, DEHNport® Maxi, DEHNbloc® NH) and surge arresters (DEHNguard®) at lightning impulse current 10/350 μs
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Overvoltage protection of low voltage systems
Figure 5.8.1.6.1 e
Decoupling inductance DEHNbridge coordinates lightning current arresters and surge arresters
decoupling inductances, the surge arresters might be overloaded, especially at the coordination between lightning current and surge arresters, and its service life being drastically reduced would mean a failure of surge protection. For the usual lightning current and surge arresters, decoupling chokes with an inductance > 10 μH are sufficiently dimensioned and a long service life for the protective combination is guaranteed. The arrester set shown in Figure 5.8.1.6.1 f, lightning current arrester, decoupling choke and surge arrester, is offered as a complete lightning current tested mains connection unit (Figure 5.8.1.6.1 g). Because of the different tasks of class C and D surge arresters, coordination between both of these arresters is also necessary. Safe coordination is guaranteed if there is at least 5 m of cable type NYM-J between the class C and D arresters (Figure 5.8.1.6.1 h). 5.8.1.6.2 Application of arresters in different system configurations. Protective measures to avoid dangerous electric shock are necessary in every electrical system. Normally live parts must be insulated, covered, sheathed or arranged to exclude contact and electric shock. This measure is called ‘protection against direct contact’. Of course, there may not be any hazard (by electric shock), but if a fault occurs (e.g., damaged insulation) there is the likelihood of accidental energization of the metallic enclosure (body of an electrical equipment). Protection against such dangers is called ‘protection in case of indirect contact’.
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Figure 5.8.1.6.1 f
Mounting assembly of the protective combination DEHNport® – DEHNbridge – DEHNguard® in the TN–C system
Figure 5.8.1.6.1 g
Mains connection box, type Netz-AK, tested by lightning impulse current
Figure 5.8.1.6.1 h
Necessary decoupling line length for class C and D arresters
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Overvoltage protection of low voltage systems
Usually, the maximum permissible permanent contact voltage UL is 50 V AC and 120 V DC. Higher contact voltages must be disconnected automatically at least after 5 s (in special cases within 0.2 s). Higher contact voltages which may arise from a fault must be disconnected automatically within 0.2 s in circuits of 35 A nominal current with socket outlets and in circuits containing class I portable equipment which is normally kept in hand during operation. In all other circuits higher contact voltages must be disconnected automatically within 5 s. Protective measures for indirect contact with protective conductors are described in IEC 60364-4-41. If triggered by fault these measures cause automatic disconnection or indication. Installing measures for ‘protection in case of indirect contact’ will entail a contract dealing with system type and protective equipment. According to IEC 60364-4-41 a complete low-voltage distribution system from the current source to the final equipment is mainly characterized by: conditions of the current source (e.g., low-voltage side of the • earthing distribution transformer) conditions of the exposed conductive parts in electrical • earthing consumer systems. There are three basic types of distribution: (i) the TN-system, (ii) the TT-system and (iii) the IT-system. These letters have the following meanings: first letter describes the earthing conditions of the feeding current • The source: ‘T’ direct earthing of one point of the current source (usually the neutral of the transformer winding) ‘I’ insulation of all active parts from earth or bonding of one point of the current source to earth via an impedance. second letter describes the earthing conditions of the exposed • The conductive parts of the electrical system: ‘T’ exposed conductive parts are directly earthed, regardless of a possible earthing of one point of the current supply ‘N’ exposed conductive parts are directly bonded with the operational earth electrode (earthing of the current source). letters describe • Further protective conductor:
the running of the neutral conductor and
‘S’ neutral conductor and protective conductor are separated ‘C’ neutral conductor and protective conductor are combined (in one conductor).
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Thus, three variants are possible for the TN-system: (i) TN–S, (ii) TN–C and (iii) TN–C–S. The following protective equipment can be installed in the different systems: protective device • overcurrent residual current device • insulation monitoring • fault voltage-operated device protective device. • As already mentioned, coordination between system type and protective equipment is necessary, as follows: (a) TN-system with: overcurrent protective device residual current device.
• •
(b) TT-system with: overcurrent protective device residual current device fault voltage-operated protective device.
• • •
(c) IT-system with: overcurrent protective device residual current device insulation monitoring device fault voltage-operated protective device.
• • • •
Protective equipment that can be installed as protection for the case of indirect contact in the different systems is as follows: protective device • overcurrent residual current device • insulation minitoring • fault voltage-operateddevice protective device. • Measures of personnel protection are of top priority in the installation of power systems. All other protective measures, such as lightning and surge protection (of electrical systems and installations) must be subordinate to the protective measures taken for the case of indirect contact with a protective conductor (considering the system type and the protective equipment) and must not be annulled by the use of protective gear (for lightning and surge protection). Also arrester faults must be taken into account (even though they would seem to be unlikely). This is especially important as lightning current and surge arresters are always installed towards the protective conductor which, however, in the case of arresters in connection with residual current circuit breakers, can lead to conflict situations.
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Overvoltage protection of low voltage systems
Figure 5.8.1.6.2 a shows an arrangement of arresters downstream of the residual current circuit breaker (seen in direction of power flow) intended to realize the ‘protection in case of indirect contact’. For such an arrangement it may occur that the surge current, which will be discharged towards the protective conductor (PE) at overvoltage limitation, is interpreted as a residual current by the upstream residual current circuit breaker. Thus, the residual current circuit breaker will try to interrupt the circuit concerned. The product standard IEC 61008-1, applicable for residual current devices, requires that residual current circuit breakers must be surge-proof, but only to an impulse amplitude of 250 A (8/20 μs) or as a selective type of residual current circuit breaker (marked by | S |) up to an impulse amplitude of 3 kA (8/20 μs). Arresters of classes B and C, provided for application in the permanent installation, however, have a much higher nominal impulse current discharge capacity. Especially in class B arresters (lightning current arresters), the residual current circuit breaker should be of such a quality (i) that it could safely carry surge currents conducted by the lightning current arrester and (ii) that there is no mistripping at such surge current stressing. A mistripping of the residual current circuit breaker is undesirable in view of the supplying safety of the consumer system and shall, therefore, be avoided. A remedy for this problem is an arrester installation (in direction of power flow) upstream of the residual current circuit breaker as shown in Figure 5.8.1.6.2 b. The discharged surge currents now no longer flow through the residual current circuit breaker and cannot be interpreted as residual current. Mistripping of the residual current circuit breaker is thus avoided. A further argument for the installation of arresters upstream of the
Figure 5.8.1.6.2 a
Installation of arresters downstream of the residual-current device (RCD)
Components and protective devices: construction, effect and application
Figure 5.8.1.6.2 b
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Installation of arresters upstream of RCD
residual current circuit breaker can be obtained from a close consideration of Figure 5.8.1.6.2 c. All parts of the electrical installation, including the arrester, are subject to overloading. Overloaded arresters will either be disconnected from the mains by the thermal disconnector according to E DIN VDE 0675 Part 6 (e.g., due to ageing reasons) or they are short-circuited by a sudden high energy input. This short-circuited arrester is a critical detail if installed downstream of the residual current circuit breaker. Because of its location between N and PE, it provides a bonding link between neutral (N) and protective conductor (PE) downstream of the residual current circuit breaker. Thus, if the equipment is faulty, as shown in Figure 5.8.1.6.2 c, the current arising over exposed conductive parts of the equipment will not be clearly identified as residual current and might, perhaps, not lead to the required disconnection of the residual current circuit breaker. This double fault which, on the one hand, provides a short-circuited arrester between N and PE although, on the other hand, defective equipment is rather rare, should also be taken into consideration when considering the safety of the personnel. If there is such a faulty arrester between N and PE in a constellation according to Figure 5.8.1.6.2 d, the residual current arising can be clearly identified at a defective piece of equipment downstream of the residual current circuit breaker, leading to a safe disconnection of the residual current circuit breaker. Therefore, arresters of classes B and C must be installed (in the direction of power flow) upstream of the residual current circuit breaker. To safeguard the ‘protection at indirect contact’ in connection with the use of arresters, especially those of classes B and C, only overcurrent protective devices are accepted as disconnection elements. A description now follows of the application of lightning current and
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Overvoltage protection of low voltage systems
Figure 5.8.1.6.2 c
Faulty arrester and faulty equipment downstream of RCD
Figure 5.8.1.6.2 d
Faulty arrester upstream of RCD and faulty equipment downstream of RCD
surge arresters in different system configurations: (i) TN, (ii) TT and (iii) IT systems. Such wiring proposals have been introduced in the German standard draft E DIN VDE 0100–534/A1. The reader should note that the solutions presented show the application of lightning current arresters in the area of the service entrance box (i.e., in the area in front of the meter). Therefore, the competent power supplying company should be approached for permission to install lightning current arresters before the meter. 5.8.1.6.2.1 TN system. For the TN-system overcurrent and residual current protective devices are permitted for ‘protection in case of indirect contact’. Lightning current and surge arresters (classes B and C) may only be installed behind overcurrent protective devices for ‘protection in
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case of indirect contact’ to safeguard measures of personnel protection also in case of an arrester fault. Arresters used in connection with fuses must be considered as overcurrent protective equipment. Depending on the strength of the next backup supply fuse and on the capacity of the arrester backup fuse, an additional separate backup fuse in the arrester branch must be provided. Rated voltages valid for the use of class B, C and D arresters in the TN system are as follows: Uc ≥ 1.1 × UN
For a 230/400 V system, this becomes URc ≥ 1.1 × 230 V = 253 V
Figure 5.8.1.6.2.1 a shows lightning current and surge arresters in the TN–C–S system. This shows that class D surge arresters are installed downstream of the residual current circuit breaker. These class D surge arresters for terminal protection usually provide transverse surge protection (surges between L and N). At a surge limitation between L and N there is no surge current discharge to PE, thus the residual current circuit breaker cannot interpret a residual current. Class D surge arresters are conceived for a nominal discharge capability of 1.5 kA (8/20 μs). On using a surge current proof residual current circuit breaker, these surge currents cannot trip or damage the residual current circuit breaker. Figures 5.8.1.6.2.1 b to e show the arresters introduced in chapters 5.8.2 to 5.8.4 within the concept of lightning protection zones and the necessary lightning and surge protection measures for a TN–C–S system. Lightning current and surge arresters in the TN–S system are shown in Figures 5.8.1.6.2.1 f to j .
Figure 5.8.1.6.2.1 a
Application of arresters in the TN–C–S system
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Overvoltage protection of low voltage systems
Figure 5.8.1.6.2.1 b
Lightning protection equipotential bonding in the TN–C system: Mounting diagram DEHNport®
Figure 5.8.1.6.2.1 c
Lightning protection equipotential bonding in the TN–C system: Mounting diagram DEHNbloc® (three pole)
Figure 5.8.1.6.2.1 d
Overvoltage protection in the TN–C system: Mounting diagram DEHNguard® / DEHNguard® T
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191
Figure 5.8.1.6.2.1 e
Overvoltage protection of the terminal equipment in the TN– C–S system: Mounting diagram surge protective device NM–DK 280 (alternative protective gear: NSM–, SF or S protector)
Figure 5.8.1.6.2.1 f
Application of arresters in the TN–S system
Figure 5.8.1.6.2.1 g
Lightning protection equipotential bonding in the TN–S system: Mounting diagram DEHNport®
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Overvoltage protection of low voltage systems
Figure 5.8.1.6.2.1 h
Lightning protection equipotential bonding in the TN–S system: Mounting diagram DEHNbloc® (three pole) / DEHNbloc® (one pole)
Figure 5.8.1.6.2.1 i
Overvoltage protection in the TN–S system: Mounting diagram DEHNguard® / DEHNguard® T
Figure 5.8.1.6.2.1 j
Overvoltage protection of terminal equipment in the TN–S system: Mounting diagram surge protective device NSMprotector (alternative protective gear: NM–DK 280, S or SF protector)
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5.8.1.6.2.2 TT-system. In the TT-system overcurrent protective devices, residual current devices and in special cases also fault voltage-operated protective devices are permitted for ‘protection in case of indirect contact’. Also here, the lightning current and surge arresters are installed downstream of the overcurrent protective devices (Section 5.8.1.6.2). By installing class B and C arresters in the TT-system the conditions for the use of overcurrent protective devices in ‘protection in case of indirect contact’ must be fulfilled. Should there be a fault (i.e., in the case of a defective arrester), currents must flow which would cause an automatic disconnection of the overcurrent protective devices within 5 s. In other words, short-circuit currents must flow. An arrester arrangement in the TT system, as in Figure 5.8.1.6.2.1 a and 5.8.1.6.2.1 f, show that for the TN system there would be no short-circuit currents in the case of a fault, but only earth-fault currents. Earth-fault currents, however, cannot trip an upstream overcurrent protective device in the required time period. Class B and C arresters in the TT system are therefore installed in L towards N. This ensures that in case of a defective arrester a shortcircuit current can be generated in the TT-system which will trip the next backup overcurrent protective device. As, however, lightning currents basically arise towards earth (PE), an N–PE arrester must form the bond between N and PE. The N–PE lightning current arrester must meet especially high demands as it must be able to carry the lightning partial currents of L1, L2, L3 and N nondestructively. The following rated voltages, Uc, are relevant to the application of arresters in the TT-system: arresters between L and N Uc ≥ 1.1 × UN
arresters between N and PE Uc ≥ 1.1 × UN × 0.5
that is, at least ≥ 250 V AC. Thus, for a 230/400 V TT system: with arresters between L and N Uc ≥ 1.1 × 230 V = 253 V
with arresters between N and PE Uc ≥ 1.1 × UN × 0.5 = 126.5 V
that is, at least UC ≥ 250 V. The lightning current-carrying capacity of class B arresters is rated in accordance with lightning protection levels I, II, III/IV of IEC 61024-1. Concerning the lightning current carrying capacity of the arresters between N and PE the following data for lightning protection level must be achieved as a minimum:
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Overvoltage protection of low voltage systems I II III/IV
Iimp ≥ 100 kA (10/350 μs) Iimp ≥ 75 kA (10/350 μs) Iimp ≥ 50 kA (10/350 μs).
Class C arresters are also installed between L and N as well as between N and PE. A discharge capacity of iN > 20 kA (8/20 μs) is required for the arrester between N and PE in connection with class C arresters. Figure 5.8.1.6.2.2 a shows lightning current and surge arresters in the TT system. As in the TN system, class D surge arresters are installed after the residual current circuit breaker. The surge current discharged by these surge arresters usually is so low that it will not be interpreted as residual current by the residual current circuit breaker. Nevertheless, a surge current proof residual current circuit breaker should be provided. Figures 5.8.1.6.2.2 b to e show installations of this kind.
Figure 5.8.1.6.2.2 a
Application of arresters in the TT system
Figure 5.8.1.6.2.2 b
Lightning protection equipotential bonding in the TT system: Mounting diagram DEHNport® / DEHNgap B
Components and protective devices: construction, effect and application
Figure 5.8.1.6.2.2 c
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Lightning protection equipotential bonding in the TT system: Mounting diagram DEHNbloc® / DEHNgap B
Figure 5.8.1.6.2.2 d Overvoltage protection in the TT system: Mounting diagram DEHNguard®/DEHNgap C, DEHNguard® T/DEHNgap C
Figure 5.8.1.6.2.2 e
Overvoltage protection of terminal equipment in the TT system: Mounting diagram surge protective adapter S/SF protector (alternative protective gear: NSM protector, NM–DK 280)
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Overvoltage protection of low voltage systems
5.8.1.6.2.3 IT-system. Overcurrent protective devices, residual current devices, insulation monitoring devices, as well as fault voltage-operated protective devices in special cases, are permitted for the IT-system as ‘protection in case of indirect contact’. Whereas, in the TN- or TT-system the ‘protection in case of indirect contact’ at first fault is guaranteed by the corresponding disconnection conditions of the overcurrent protective devices or residual current devices, there is only an indication of fault in the IT-system. A contact voltage that is too high cannot occur because an earth reference is made in the IT-system at first fault. With regard to its operating state, the IT-system then changes over into a TN- or TTsystem. An IT-system can, therefore, safely continue after the first fault, so that processes or productions (e.g., in the chemical industry) already begun can still be finished. At the first fault the protective conductor PE takes the potential of the defective phase, which is not dangerous because through the protective conductor all exposed conductive parts and touchable metal parts have this potential, so there are no dangerous potential differences to be bridged. Nevertheless, it must be considered that in case of the first fault, the IT-system potential of the non-faulty conductors to earth corresponds to the potential between the phases. Thus, in a 230/400 V IT-system there is a potential of 400 V at the non-faulty arresters in the case of a defective arrester. This possible operating state must be taken into account on selecting the arresters with regard to their rated voltage. For the use of arresters of class B, C and D in the IT-system the following rated voltages are applicable: Uc ≥ 1.1 × UN × √ 3
thus, for a 230/440 V–IT-system, Uc ≥ 1.1 × 230 V × √ 3 Uc > 440 V
For a second fault in the IT-system a protective device must then be tripped. With respect to the use of arresters in the IT-system in connection with a protective device for the ‘protection in case of indirect contact’ the statements of section 5.8.1.6.2 are applicable. Thus, in the IT-system too, the installation of class B and class C arresters upstream of the residual current circuit breaker is advisable. Figure 5.8.6.2.3 a shows lightning current and surge arresters in the IT-system. Different arresters in the IT-system are shown in Figures 5.8.1.6.2.3 b and c. 5.8.1.6.3 Selection of arrester backup fuses. Arrester data sheets usually indicate the maximum permissible backup fuse for the arrester. This indication is required by the product standards IEC 61343-1/DIN VDE 0675 part 6.
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Figure 5.8.1.6.2.3 a
Application of arresters in the IT system
Figure 5.8.1.6.2.3 b
Lightning protection equipotential bonding in the IT system: Mounting diagram DEHNport®
Figure 5.8.1.6.2.3 c
Surge protection in the distribution cabinet in the IT system: Mounting diagram DEHNguard® / DEHNguard® T
The primary task of this arrester backup fuse is to safeguard the shortcircuit capability. Standardized testing of the arrester’s short-circuit capability will prevent dangerous sparking of the arrester in the case of an internal short circuit (which may be due to a surge current that exceeds the nominal discharge capacity of the arrester) and the generated 50 Hz short-circuit current. Special types of arrester have integrated this
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backup fuse in their enclosure. Most arresters on the market, however, are not equipped with such a backup fuse. Therefore, the next upstream system fuse can be taken as the backup fuse for the arrester if its nominal value does not exceed that of the maximum permissible fuse (Figure 5.8.1.6.3 a). If, however, the nominal value of the system fuses F1–F3 exceeds the nominal value of the maximum backup fuses for the arresters, separate backup fuses having the nominal value of the maximum permissible backup fuse must be installed before the arrester (Figure 5.8.1.6.3 b). In addition to securing short-circuit capability there is still another function of an arrester backup fuse which is especially important for class B arresters (lightning current arresters). These are mostly designed as spark gap arresters in view of the high electrical and mechanical stress on discharging a lightning current. This guarantees a high nominal discharge capability of the arrester. Spark gap arresters generate a 50 Hz
Figure 5.8.1.6.3 a
Use of system fuses as arrester backup fuses
Figure 5.8.1.6.3 b
Application of separate arrester backup fuses
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mains follow-current which must be safely quenched after the decay of the lightning interference. This mains follow-current can be as high as the prospective short-circuit current at the place of installation of the lightning current arrester. Spark gap arresters are usually able to quench mains follow-currents having a prospective short-circuit current value of about 4 kAeff (50 Hz). If the prospective short-circuit current exceeds the arrester mains follow-current quenching capability, the backup fuse must disconnect the mains follow-current. Most service entrances have a prospective short-circuit current below 3 kAeff (50 Hz) so that there are few practical cases where the backup fuse must disconnect a mains follow-current higher than 4 kA. In particular, arresters based on spark gaps (i.e. lightning current arresters), due to the operation of which a mains follow-current can be generated, load their upstream fuses (arrester backup fuses) with mains short-circuit currents. To keep this loading of parts of the power system as low as possible, the spark gaps must be designed in such a way that not every discharge process generates a mains follow-current. Spark gaps meeting these requirements are constructed as multiple gliding spark gaps (as used in the lightning current arresters DEHNport©, DEHNbloc©, DEHNbloc© NH). On the operation of this type of spark gap, two partial arcs will be generated which oppose the emergence of a mains follow-current already from the beginning of the arc by the total voltage drop of both arcs. In Figure 5.8.1.6.3 c a lightning current arrester with tandem gliding spark gap is compared with a usual simple spark gap with respect to the frequency of a generated mains follow-current. This diagram reveals that
Figure 5.8.1.6.3 c
Comparison of the follow-current frequency (in %) of lightning current arresters with spark gaps
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mains follow-currents are less frequent with a multiple gliding spark gap and that the stressing of the arrester backup fuse and the upstream power system by mains short-circuit currents is considerably reduced. With respect to the use of lightning current arresters in power systems and fuses it must be taken into account that they are first loaded by lightning surge currents followed by the mains short-circuit currents. In contrast to mains follow-currents, lightning surge currents in the power system cannot be avoided as these are impressed currents. The performance of NH fuses at lightning surge current loading has been closely examined. Figure 5.8.1.6.3 d shows the fuse characteristics. Depending on the nominal current of the fuse and the surge current in the test, there are three different characteristics of NH fuses: (i) no melting, (ii) melting and (iii) explosion. (i)
(ii)
No melting. The energy input by the lightning surge current is too low for the fuse strip to be melted. An installation of the arresters (according to Figure 5.8.1.6.3 a) guarantees the continued supply to the downstream consumer as is the case at a configuration according to Figure 5.8.1.6.3 b. Melting. The energy of the lightning surge current is high enough to melt the fuse strip of the NH fuse and thus to interrupt the current path through the fuse. Figure 5.8.1.6.3 e shows the oscillogram of a fuse melting by lightning surge currents. Typical for the fuse performance is that the impressed lightning surge current keeps on flowing without being influenced by the behaviour of the fuse. After the melting integral of the fuse has been exceeded by the lightning surge current, an arc will be generated in the fuse which will be realized by the potential over the fuse. For the arrester configuration according to Figure 5.8.1.6.3 a, the
Figure 5.8.1.6.3 d
Performance of NH fuses during the impulse current loading 10/350 μs
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Figure 5.8.1.6.3 e
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Current and voltage at a melting 25 A NH fuse during a lightning impulse current loading (10/350 μs)
downstream consumer system then will be disconnected. Thus, the solution variant according to Figure 5.8.1.6.3 b comes to the fore. Sometimes it is suggested to choose fuses of size F4–F6 selectively to the fuses F1–F3. Practically this means that the relation of the nominal currents of the fuses F1–F3 to F4–F6 is 1.6: 1. This selective characteristic of fuses is only relevant with regard to the mains follow-currents (50 Hz) but not with regard to lightning surge currents. To emphasize this statement consider the following example. Under the aspect of selectivity let the nominal current of the fuses F1–F3 be 160 A and the nominal current of the fuses F4–F6 be 100 A. This configuration is loaded by a lightning surge current of 25 kA (10/350 μs) for each path. At such a loading F1–F3 as well as F4–F6 will be tripped according to Figure 5.8.1.6.3 d. Such a configuration is not selective under lightning surge current loading! Thus, the downstream consumer system would be disconnected. More severely still, the voltage drop of the melting fuses F4–F6 2 kV (according to 5.8.1.6.3 e) occurs in the arrester branch, that is to say in parallel with the protected consumer-system. This voltage drop is a driving voltage for downstream arresters and might cause their overloading. To avoid this effect, arrester fuses F4–F6 must be as strong as possible which, in practice, means that F4–F6 only must be used, if F1–F3 are stronger than the indicated maximum permissible arrester backup fuse. The nominal current of F4–F6 then shall be as high as the maximum permissible arrester backup fuse. (iii) Explosion. The energy of the lightning surge current is so high that the fuse strip of the NH fuse evaporates in an explosion. As a result, the enclosure of the NH fuse may split (Figure 5.8.1.6.3 f). Beside these mechanical
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Different problems require solutions for the arrester backup fuses in their fields of application. Consider the following: (i)
Protection against indirect contact in case of defective arresters. This is the task of the backup fuses of all arresters of classes B, C and D (for arresters in class D, additional residual current circuit breakers can be used). For this purpose the fuses must be designed in such a way that the defective arresters will be safely disconnected from the low-voltage system in the required time. (ii) Securing short-circuit withstand capability of the arresters. To guarantee the short-circuit withstand capability indicated by the producer the permitted maximum backup fuse must, under no circumstances, be exceeded. (iii) Disconnection of too high mains follow-currents. Particularly in the case of lightning current arresters based on spark gaps, mains follow-currents may arise. On application of the permitted maximum backup fuse, the maximum follow-current quenching capacity of the arrester is also
Figure 5.8.1.6.3 f
NH fuse burst due to lightning impulse current loading
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reached. If there is a weaker backup fuse, mains follow-currents will be disconnected which might be safely quenched by the arrester itself. Therefore, the backup fuse of a lightning current arrester must be as strong as possible and separate backup fuses in the arrester branch should be avoided if the system conditions allow it.
If the system fuses F1–F3 (Figure 5.8.1.6.3 b) are weaker than the maximum permitted arrester backup fuse and additionally F1–F6 are required (allowing the disconnection of the arrester branch for maintenance) then for F4–F6 NH-disconnecting blades should be used. To conclude the subject of ‘arrester backup fuses’ consider yet again the follow-current extinguishing capability of the lightning current arrester DEHNport® Maxi introduced in section 5.8.1.2. Figure 5.8.1.6.3 g shows the typical breaking oscillogram (uninfluenced short-circuit surge current 37 kAeff’, cos φ = 0.23) of the arrester DEHN® Maxi in RADAX-flow technology. The spark gap arc voltage shown in the left part of the Figure is in its amplitude almost equal to the system voltage. The typical ‘dipping’ of the system voltage of conventional spark gaps will not occur. This excludes interference in electronic devices which are sensitive to voltage dips or voltage supply deviations. In the right part of the oscillogram the effective limitation of the mains follow-current is readable. It represents the uninfluenced (i.e., the theoretically possible) as well as the following short-circuit current through the arrester. Obviously it is only a very low share of the theoretically possible current that loads the arrester and thus the whole low voltage system. A further effect of the high arc resistance is the reduction of the duration of current flow. The oscillogram shows that, even in case of an impulse short-circuit current of 37 kAeff, the pre-arcing current through the examined arrester in RADAX-flow technology is only about 1.7 kA. If this value is transferred to a diagram, as is usual for the selectivity considerations of overcurrent protective devices (fuses, circuit breakers), one obtains Figure 5.8.1.6.3 h. This shows the let-through current integral (∫ I 2t) of a RADAX-flow arrester at different short-circuit currents. For better classification the melting integrals of NH fuses of different nominal currents
Figure 5.8.1.6.3 g
Interruption of a short-circuit current by RADAX-flow technology (DEHNport® Maxi)
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Figure 5.8.1.6.3 h
Selectivity limit current DEHNport ® Maxi at different backup fuses
are indicated. Arresters in RADAX-flow technology can, as Figure 5.8.1.6.3 h shows, effectively limit short-circuit currents of 50 kAeff. The integral of the let-through current remains lower than the melting integral of a 40 A NH fuse, meaning that this fuse will not trip. The letthrough current limitation secures the selectivity between the overcurrent protective devices in the low-voltage consumer system and the lightning current arresters. On using an arrester of class B (lightning current arrester) in RADAX-flow technology in the main current supply system the tripping of the backup fuse at the service entrance or meter board by mains follow currents is avoided. Operation of the lightning current arrester remains practically unnoticed by the user.
Sources IEC 61643–1: ‘Surge protective devices connected to low-voltage power distribution systems – Part 1: Performance requirements and testing methods’. International Electrotechnical Commission, 3 rue de Varembe, Geneva, Feb. 1998 E DIN VDE 0675 Teil 6: ‘Überspannungsableiter zur Verwendung in Wechselstromnetzen mit Nennspannungen zwischen 100 V und 1000 V’. (VDE Verlag, GmbH, Berlin/Offenbach) Nov.1989 E DIN VDE 0675-6/A1 (VDE 0675 Teil 6/A1): ‘Überspannungsableiter zur Verwendung in Wechselstromnetzen mit Nennspannungen zwischen 100 V und 1000 V’. Änderung A1 zum Entwurf
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DIN VDE 0675-6 (VDE 0675 Teil 6) (VDE Verlag, GmbH, Berlin/Offenbach) March 1996 E DIN VDE 0675-6/A2 (VDE 0675 Teil 6/A2): ‘Überspannungsableiter. Teil 6: Verwendung in Wechselstromnetzen mit Nennspannungen zwischen 100 V und 1000 V’. Änderung A2 zum Entwurf DIN VDE 0675-6 (VDE 0675 Teil 6) (VDE Verlag, GmbH, Berlin/Offenbach) Oct. 1996 IEC 61312-1: ‘Protection against lightning electromagnetic impulse – Part 1: General principles’. International Electrotechnical Commission, Geneva, Feb. 1995 IEC 60664-1: ‘Insulation coordination for equipment within low-voltage systems – Part 1: Principles, requirements and tests. International Electrotechnical Commission, Geneva, Oct. 1992 IEC 60364-4-41: ‘Electrical installations of buildings – Part 4: Protection for safety’. Chapter 41: ‘Protection against electric shock’. International Electrotechnical Commission, Geneva, Oct. 1992 IEC 61008-1: ‘Residual current operated circuit-breakers without integral overcurrent protection for household and similar uses (RCCBs). – Part 1: General principles’. International Electrotechnical Commission, Geneva, Dec. 1996 IEC 61024-1: ‘Protection of structures against lightning – Part 1: General principles’. International Electrotechnical Commission, Geneva, March 1990 E DIN VDE 0100-534/A1 (VDE 0100 Teil 534/A1): ‘Elektrische Anlagen von Gebäuden. Auswahl und Errichtung von Betriebsmitteln. Schaltgeräte und Steuergeräte, Überspannungs-Schutzeinrichtungen – Änderung A1 (Vorschlag für eine Europäische Norm)’. (VDE Verlag, GmbH, Berlin/Offenbach) Oct. 1996 DEHN u. SÖHNE: ‘Installation of SPD for power supply systems and equipment’. DS 655/E/397. (Dehn + Söhne, Neumaret) March 1997 DEHN u. SÖHNE: ‘Energy coordination – The selective surge protection’. DS 641/E/597. (Dehn + Söhne, Neumaret) May 1997 HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’ (VDE Verlag, Berlin; Pflaum Verlag, München, Fourth edn, 1993) HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept’ (VDE Verlag, Berlin; Pflaum Verlag, München, 1993) RAAB, V.: ‘Blitz und Überspannungsschutz-Massnahmen in NS-Anlagen’, Elektropraktiker, Berlin, Teil 1, 1996, 50, (11), pp. 944–951; Teil 2, 1996, 50, (12), pp. 1043–1046. HASSE, P., and EHRLER, J.: ‘Konzeptionelles Vorgehen beim Blitz und Überspannungsschutz komplexer Anlagen’, Elektrotechnik, 1996, (2), pp. 53–58; 1996, (3), pp. 69–73; 1996, (6), pp. 49–54. POSPIECH, J., NOACK, F., BROCKE, R., HASSE, P., and ZAHLMANN, P.: ‘Blitzstrom–Ableiter mit Selbstblas-Funkenstrecken – Ein neues Wirkprinzip für den Blitzschutz in Niederspannungsnetzen’, Elektrie, Berlin, 1997, 51, pp. 9–10. RAAB, V., and ZAHLMANN, P.: ‘Folgestrombegrenzender Blitzstrom-Ableiter für Hauptstromversorgungssysteme’, Elektropraktiker, Berlin, 1997, 51, p. 12. HASSE, P., ZAHLMANN, P., POSPIECH, J., and NOACK, F.: ‘Generationswechsel bei Blitzstrom–Ableiter für Niederspannungsanlagen’, etz, 1998, No. 7–8
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5.8.2 Arresters for information technology According to IEC 61644-1/DIN VDE 0845 the generic term ‘surge protective devices (SPDs)’ in the field of information technology does not only mean modules but also includes protective circuits which limit the overvoltages in systems and equipment to permissible values. Protective circuits gradually reduce surges by the series connection of overvoltage limiting modules and decoupling elements (Figure 5.8.2 a). Overvoltage limiting elements with decreasing limiting voltage and decreasing energy loadability are connected in series. Decoupling elements can be resistors, inductors, capacitors or filters. There are two types of arrester depending on the requirements and loading at their place of installation in accordance with the concept of lightning protection zones. These are, namely, (i) lightning current arresters (which are tested by an impulse current wave 10/350 μs) and (ii) surge arresters (which are tested by an impulse current wave 8/20 μs). Highest demands, with regard to their discharge capability, are made on lightning current arresters. Within the scope of the lightning and surge protection system they are installed at the interface of the lightning protection zone 0A/1. They prevent disturbing lightning partial currents from penetrating into the information technology network. To guarantee interference-free and surge-proof operation of information technology equipment a disturbance arising in the information system must be limited to a level which is below the interference or destruction limit of the equipment. The interference and destruction
Figure 5.8.2 a
Graded protection (stepped protection in accordance with DIN VDE 0845)
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limits of the equipment, however, are largely unknown and not indicated. A starting point is offered by the indicated surge immunity against impulse shaped surges which has been tested in EMC surge immunity tests according to IEC 61000-4-5/EN 61000-4-5. To avoid disturbances or even the destruction of information technology equipment, surge arresters must limit the disturbing influences to values below the surge immunity of the equipment to protect. In contrast to the selection of protective devices in power systems which have uniform conditions in the 230/400 V system regarding voltage and frequency, there are different kinds of signals to be transmitted in information technology systems in terms of the following:
• • • • •
voltage current signal supply frequency type of signal
(e.g., 0–10 V) (e.g., 0–20 mA, 4–20 mA) (symmetrical, unsymmetrical) (DC, LF, HF) (analogue, digital).
Each of these electrical parameters of the signal to be transmitted can contain the information which shall be actually transmitted. Signals must therefore not be influenced by the installation of lightning current and surge arresters in information technology systems. As for power engineering, there are different types of arresters for the individual places of application in the information technology, such as (i) in a permanent installation (Figure 5.8.2 b), (ii) at socket outlets (Figure 5.8.2 c) and (iii) at equipment inputs (Figure 5.8.2 d). Figure 5.8.2 e shows the installation of lightning current and surge arresters at computing centre interfaces in accordance with the concept of lightning protection zones. To reduce the influence of the electromagnetic field, building or room shielding measures have been realized at the interfaces of lightning protection zones 0 and 1 as well as at lightning protection zones 1 and 2, as has already been detailed in Section 5.2. The power system is included into the lightning protection equipotential bonding by lightning current arresters at the interface of lightning protection zones 0 and 1. The local equipotential bonding at the transition of the lines from lightning protection zones 1 to 2 is achieved by surge arresters. The surge protection of the information technology system is structured analogously. Arresters used in the information technology side of a system protected as described will be introduced by way of examples in the following Sections. To facilitate understanding the protective devices are classified according to whether they are mainly used in measuring and control systems (chapter 5.8.2.1) or mainly in data networks/systems (chapter 5.8.2.3). Combined protective devices for power and information technology equipment inputs (chapter 5.8.2.2) are also introduced.
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Figure 5.8.2 b
Blitzductor®s CT for protecting the measuring and control technology of a petrochemical system (installed in a protective cabinet)
Figure 5.8.2 c
Data socket outlets with surge arresters
Figure 5.8.2 d
Pluggable surge arresters for use at terminal equipment
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Figure 5.8.2 e
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Lightning partial current proof interface connection for a computer centre with asymmetrical interface (V24/RS 232 C)
Sources IEC 61644-1 Ed.1: ‘Surge protective devices connected to telecommunications and signalling networks – Part 1: Performance requirements and testing methods’. International Electrotechnical Commission, Geneva, Oct. 1998 DIN VDE 0845 Teil 1: ‘Schutz von Fernmeldeanlagen gegen Blitzeinwirkungen, statische Aufladungen und Überspannungen aus Starkstromanlagen. Massnahmen gegen Überspannungen’ (VDE Verlag, GmbH, Berlin/ Offenbach) Oct. 1987 E DIN VDE 0845 Teil 2: ‘Schutz von Einrichtungen der Informationsverarbeitungs und Telekommunikationstechnik gegen Blitzeinwirkungen, Entladung statischer Elektrizität und Überspannungen aus Starkstromanlagen. Anforderungen und Prüfungen von Überspannungs-schutzeinrichtungen’ (VDE Verlag, GmbH, Berlin/Offenbach) Oct. 1993 IEC 61000-4-5: ‘Electromagnetic compatibility (EMC) – Part 4: Testing and measurement techniques (Section 5): Surge immunity test’. International Electrotechnical Commission, Geneva 1995 HASSE, P., and WIESINGER, J.: ‘EMV-Blitz-Schutzzonen-Konzept München (Pflaum Verlag, Berlin/Offenbach: VDE Verlag, Berlin/Offenbach) DEHN u. SÖHNE: ‘Selection and installation of surge protective devices. Type Blitzductor® CT for protection of control and instrumentation systems acc. to IEC 61312-1. DS 656/E/897’, Aug. 1997
5.8.2.1 Arresters for measuring and control systems Blitzductor®s as protective devices for measuring and control systems have had a proven record for decades. The energy coordinated arrester family Blitzductor® CT will serve as an example to describe the construction, effects and application of this type of arrester.
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5.8.2.1.1 Blitzductor® CT: Construction and mode of functioning. The Blitzductor® CT is designed in two parts (Figure 5.8.2.1.1 a): Protection modules are fitted on a universal base (which can be used almost independently from the operating parameters of the circuit to be protected like a modular terminal block). The Blitzductor® CT, as a fourpole structure (Figure 5.8.2.1.1 b), has two input and two output terminals to connect one double wire (type D) or two single wires (type E). Since it has a width of only 12 mm (2/3 module) and a height of 58 mm a space-saving installation is possible. A choice of more than 40 protective modules is available to provide for optimal discharge capability, protection and performance of the surge protective device for the interface to be protected. These can be plugged into the universal base (Figure 5.8.2.1.1.c, a). By means of a contact
Figure 5.8.2.1.1 a
Blitzductor® CT with different protective modules
Figure 5.8.2.1.1 b
Blitzductor® CT, type MD, for application in earth-free signal lines (e.g., telephone lines)
Components and protective devices: construction, effect and application
Figure 5.8.2.1.1 c
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(a) Blitzductor® CT: left: plug-in protective module; right: base
mechanism in the base, the protective module can be exchanged during its live state without interruption of the signal transmission. With these base elements a universal pre-wiring of the system becomes possible without even knowing the later operating parameters. If, later, the operating parameters are known then adequate protective modules are employed. This changes the modular terminal blocks into an adjusted protective device. This is particularly advantageous when planning in accordance with the concept of lightning protection zones. Use of the Blitzductor® CT bases, which will be already inserted at the pre-installation stage, means that space can be reserved for complete surge protection. The protective devices are safely earthed via the DIN rail (according to EN 50 0229) and the snap-on base support. To realize the complex protection philosophy there are also screen terminals at the base (for contacting the screens of cables). Direct or indirect earthing of the cable screen is possible by the insertion of a gas discharge arrester into the base bay (Figure 5.8.2.1.1 c, b). Thus earthing and equipotential bonding systems can be realized which are adjusted according to the system to protect. There are three ‘performance categories’ of the Blitzductor® CT. These protective types of module include: (i) the lightning current arrester, (ii) the surge arrester and (iii) the combined arrester. Thus (i)
(ii)
Protective module type B (Figure 5.8.2.1.1 d) is designed as a ‘lightning current arrester’ for impulse currents Iimp: 2.5 kA (per wire) wave shape 10/350 μs. Protective module type M is dimensioned as a ‘surge arrester’ for nominal discharge currents isn: 10 kA (per wire) wave shape 8/20 μs (Figure 5.8.2.1.1 e).
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Figure 5.8.2.1.1 c
(b) Blitzductor® CT: left: contacts: base/protective module; right: circuit
Figure 5.8.2.1.1 d
Blitzductor® CT, protective module type B: top: basic circuit diagram; bottom: rated discharge current IIMP = 2.5 kA (10/350 μs) per wire
Figure 5.8.2.1.1 e
Rated discharge current isn = 10 kA (8/20 μs) for protective modules, type M
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module ME (Figure 5.8.2.1.1 f) protects earthed signal • Protective wires (a typical application is for example the Pt 100 four-phase
• • •
measurement). Protective module MD (Figure 5.8.2.1.1 g) is provided for non-earthed wire pairs (as for symmetric signal wires which are connected via isolating transformers). Protective module ME/C (Figure 5.8.2.1.1 h) protects optocoupler inputs or inputs with intrinsic protective circuit (clamping diodes) and therefore has decoupling resistors at the output. Protective module MD/HF is designed for the protection of HFtransmission links and is equipped with a diode-matrix (Figure 5.8.2.1.1 i).
Figure 5.8.2.1.1 f Basic circuit diagram, module ME
Figure 5.8.2.1.1 g Basic circuit diagram, module MD
Figure 5.8.2.1.1 h Basic circuit diagram, module ME/C
Figure 5.8.2.1.1 i Basic circuit diagram, module MD/HF
Figure 5.8.2.1.1 j
Basic circuit diagram, module MD/Ex
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Overvoltage protection of low voltage systems module MD/Ex (Figure 5.8.2.1.1 j) (having a 500 V AC • Protective withstand capability to earth) is provided for instrinsically safe meas-
uring circuits. (iii) Protective module B is designed as a ‘combined arrester’ for impulse currents Iimp: 2.5 kA (10/350 μs) per wire, however, with a protection level like a surge arrester protective module M (Figure 5.8.2.1.1 k).
Basically, there are two types of Blitzductor® CT: E types (for connecting two single wires and for limiting surges between every wire and earth) and D types (for connecting a double wire and for limiting surges between the two wires). The voltage limiting characteristic of both types is shown in Figure 5.8.2.1.1 l. Other characteristics to consider include: (i)
Nominal voltage. The nominal voltage indication on the Blitzductor®s CT is the upper value of the signal voltage range which can be transmitted over the protective device under nominal conditions without any limiting effects of the protective device. The nominal voltage is indicated as a DC
Figure 5.8.2.1.1 k
Blitzductor® CT, protective module type B . . . . Top: basic circuit diagram; bottom: rated discharge current IIMP = 2.5 kA (10/350 μs) per wire, however, protective level like surge arrester (M)
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Figure 5.8.2.1.1 l
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Surge limitation of the Blitzductor® CT types . . . E and . . . D
value. On AC voltage transmission the AC peak value must not exceed the specified nominal voltage. Figure 5.8.2.1.1 m shows nominal voltages for different types of Blitzductor® CT. (ii)
Protection level. The protection level of the Blitzductor® CT characterizes its performance in limiting the output voltage. The specified protection level value is higher than the maximum value of the limiting voltages in the tests, the measured limiting voltage being the maximum voltage measured at the terminals of the surge protective device during the loading with surge currents and/or surge voltages (with specified impulse waveshape and amplitude). The standardized procedure is as follows. voltage at a 1 kV/μs steepness of the applied test impulse • Limiting This test (Figure 5.8.2.1.1 n) determines the operating characteristic of gas discharge arresters. These protective elements have a ‘switch characteristic’: The mode of function of a gas discharge arrester can be described as a switch, the resistance of which can ‘jump’ automatically from > 10 GΩ (in the inactive state) to values < 0.1 Ω (active state) if a certain voltage is exceeded, so that the overvoltage is almost shortcircuited (Figure 5.8.2.1.1 o). The activating voltage of the gas discharge arrester depends on the rate of rise (du/dt) of the incoming impulse. Hence, the higher the rate of time the higher the activating voltage of the gas discharger arrester. To compare the operating values of different gas discharge arresters a rate of rise of 1 kV/μs will be applied at the electrodes of the gas discharge arrester and the activating value will be determined. voltage at nominal discharge current • Limiting This test (Figure 5.8.2.1.1 p) is for determining the limiting characteristic (Figure 5.8.2.1.1 q) of protective elements with constant limiting characteristic.
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Figure 5.8.2.1.1 m
Nominal voltage data for different Blitzductor® CT types
Figure 5.8.2.1.1 n
Test assembly for the determination of the limiting voltage at a voltage rate of rise du/dt = 1 kv/μs
Figure 5.8.2.1.1 o
Sparkover characteristic of a gas-filled surge arrester, at du/dt = 1 kv/μs
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Figure 5.8.2.1.1 p
Test assembly for the determination of the limiting voltage at nominal discharge current isn
Figure 5.8.2.1.1 q
Limiting voltage at nominal discharge current
(iii) Nominal current The nominal current IN of the Blitzductor® CT characterizes the maximum permissible operating current of the measuring and control circuit to protect (Figure 5.8.2.1.1 r ). IN is determined by the current carrying capacity and the power loss of the impedances used for the decoupling between gas discharge arresters and fine protective elements and by the follow-current extinguishing capability of the gas discharge arresters. It is indicated as a DC value. Table 5.8.2.1.1 a indicates the nominal currents of different types of Blitzductor® CT. (iv) Cut-off frequency The cut-off frequency describes the behaviour of the Blitzductor® CT in relation to frequency (Figure 5.8.2.1.1 s). The cut-off frequency is the frequency which causes (under defined test conditions) an attenuation loss aE of 3 dB (compare E DIN VDE 0845 Part 2: 1993-10). This frequency usually refers to a 50 Ω system.
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Figure 5.8.2.1.1 r
Nominal current of Blitzductor® CT
Table 5.8.2.1.1 a
Nominal currents of the Blitzductor® CT-types
Figure 5.8.2.1.1 s
Typical frequency response of a Blitzductor® CT
(v)
Energy coordination, coordination characteristics The regulations for energy coordination specified in section 5.8.1.6.1 are also valid for information technology systems. Owing to the low operating currents of these systems, however, a coordination of arresters by ohmic resistor elements is also possible here. The Blitzductor® CT has integrated decoupling elements so that external decoupling measures can be avoided: These protective devices can be directly installed side by side.
Whereas, in the case of a low-voltage consumer system, one can generally proceed from a surge immunity of the system which has been specified in the scope of the insulation coordination, proceeding along similar lines would be a failure for information technology interfaces. Only by legal demands for an adequate immunity of the interfaces of information technology equipment due to the EC-general regulations for EMC and the standardization of reproducible testing methods is it possible to describe the important parameters needed for the surge protection of
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input circuits. To decide whether the equipment to protect can withstand the residual let-through impulse of an upstream arrester, a comparison of the arrester let-through parameters and the impulse parameters of the specified equipment interface immunity is necessary. This point is shown in Figure 5.8.2.1.1 t. The standard series IEC 61000-4 . . . /EN 61000-4 . . . has been stated for testing a piece of equipment with regard to its immunity against various electrical transients. Testing with high-energy transient surges as they arise for the case of switching overvoltages or induced lightning overvoltages is described in IEC 61000-4-5/EN 61000-4-5. As the description of the interference immunity test reveals, there are parallels to the voltage proof test of insulations. However, on analysing both testing procedures as well as their final background and the test techniques used it is observed that the only common parameter of the tests is the voltage impulse wave of 1.2/50 μs of the unloaded generator. Although the ‘voltage proof test’ examines the insulation of the test object, thus interpreting by this means ‘sparkover’ or ‘puncturing’ of the insulation as a failure, the specimen might otherwise ‘react’ in the ‘interference immunity test’. Such a reaction, for example, can be the limitation of the test impulse by means of protective elements (diodes, varistors, gas discharge arresters). In contrast to the voltage proof test, this reaction or response of the protective elements is not considered as a failure. Functional endurance, during the test, is the most important, so that depending on the test specimen, a temporary degradation of the performance is permissible. In addition to the differences in testing approach and evaluation of both tests there is another considerable difference in the current–time loadings at the ‘response’ of the test specimen. Whereas the current flow, in the case of insulation sparkover or puncture in the test circuit, is usually almost negligible at voltage proof tests, there will be an energetic loading caused by the impulse current at the response of the device protection during the interference immunity test. The kind of testing used for the equipment to protect is important for the dimensioning of surge protective devices for information technology:
Figure 5.8.2.1.1 t
Basic mode of functioning of the Blitzductor® CT
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Overvoltage protection of low voltage systems
a given voltage surge withstand capability the output level of the • At arrester only must be below the voltage surge withstand capability of
•
the terminal equipment in order to guarantee a sufficient protection. If, however, the dimensioning of the arrester depends on the given interference immunity of the terminal equipment, both of the following conditions must be met: (i) the protection level of the arrester must be lower than the voltage surge withstand capability of the terminal equipment; and (ii) the maximum output energy of the arrester must be lower than the maximum permissible input energy of the terminal equipment (Figure 5.8.2.1.1 u).
To decide whether the equipment to protect withstands the residual let-through impulse of a Blitzductor® CT, a comparison of the Blitzductor®-let-through values with the impulse parameters of the interference immunity test specified for the equipment interface (acc. to IEC 61000-4-5/EN 61000-4-5) (Figure 5.8.2.1.1 n) must be carried out. By introducing ‘coordination characteristics’ (KK) (Figure 5.8.2.1.1 v) a Blitzductor® CT can easily be coordinated with the equipment to be protected: characteristics provide information about the discharge • Coordination capability of the Blitzductor CT (input characteristic) and about its ®
•
protective effect related to a 2 Ω hybrid impulse (output characteristic). By determining the permissible input loading of the equipment interface, based on its basic interference immunity conforming to standards, the coordination characteristic (input characteristic) of each interface can be ascertained and is comparable to the output characteristic of the coordination characteristic of the Blitzductor® CT.
Figure 5.8.2.1.1 u
Verification of safe coordination by comparison of the admissible energy loading of a device interface tested in accordance with standard IEC 61000-4-5 with the ‘cut-off energy’ of the protector Blitzductor® CT
Components and protective devices: construction, effect and application
Figure 5.8.2.1.1 v
221
Coordination characteristics (KK) of the Blitzductor® CT family
Analogously to such an ‘adjustment’ of the Blitzductor® CT to the equipment interface the ‘coordination’ of cascaded Blitzductor®s CT can be achieved. In addition to the operating parameters (such as operating voltage, nominal current, transmission frequency etc.) it only need be considered that the ‘input’ of a Blitzductor® CT or terminal equipment must fit with the ‘output’ of an upstream Blitzductor® CT. The necessary ‘input’ of the first Blitzductor® CT (of this mutually and equipment coordinated ‘protective chain’) is determined by the threatparameters of the whole system. Figure 5.8.2.1.1 w shows such a coordination with the protector family Blitzductor® CT under application of the coordination characteristics (KK). Blitzductor® CT types, with their coordination characteristics (KK), are listed in Table 5.8.2.1.1 b. A protective cascade, as designed by the producer under the aspects of sufficient safety such as the protector Blitzductor® CT family, is able to guarantee in a modern concept of lightning protection the trouble-free running of the system over a long period of time. Thus, the integral responsibility of the arrester producer is becoming a new factor in the cooperation of protector producer and protector applier at a time when the producer liability is of special importance.
Sources EHRLER, J., and HASSE, P.: ‘Energetisch koordinierte Überspannungsschutzgeräte erfüllen die Anforderungen moderner Informationstechnik’, Elektrotechnik, 1996, (12), pp. 73–76 DEHN + SÖHNE: ‘Blitzductor® CT. Energy coordination in communication/ signalling systems’. DS 643/E/197 DEHN + SÖHNE: ‘Selection and Installation of surge protective devices. Type Blitzductor® CT for protection of control and instrumentation systems acc. to IEC 61312-1’. DS 656/E/Aug. 1997
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Figure 5.8.2.1.1 w
Table 5.8.2.1.1 b
Example for the energy coodinated application of the Blitzductor® CT by means of their coordination characteristics (KK) Blitzductor® CT types and their coordination characteristics
HASSE, P., and ZAHLMANN, P.: ‘Koordinierter Einsatz von Blitzstrom und Überspannungs-Ableitern im Blitzschutz – Umsetzung von DIN VDE 0185 Teil 103, E DIN VDE 0675 Teil 6, Teil 6/A1, Teil 6/A2 und E DIN VDE 0100 Teil 534 A1 in die Praxis. 2 (VDE/ABB Fachtagung, Neu Ulm, Nov. 1997) IEC 61000-4-5: ‘Electromagnetic compatibility (EMC) – Part 4: Testing and measurement techniques – (Section 5): Surge immunity test. International Electrotechnical Commission, Geneva 1995
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5.8.2.1.2 Blitzductor® CT: Selection criteria. Ten of the most important selection criteria (SC) for arresters in measurement and control systems are presented here through the example of the Blitzductor® CT protector family. Their application will be described. SC A: What discharge capability is necessary? Types B . . . or M . . . ? The selection of the discharge capability of the Blitzductor® CT depends upon which protection requirements shall be fulfilled by this arrester. A distinction has to be made as to whether the measurement and control system (or the telecommunication system) is only endangered by surges (which are effective as impulse currents being simulated by a 8/20 μs wave) or whether by partial lightning currents (simulated by 10/350 μs impulse currents): protection, MCR-cable leading beyond the building. In this • Lightning case (Figure 5.8.2.1.2 a) the terminal equipment to be protected is in a
•
building with lightning protection. The measuring, controlling and regulating (MCR) or telecommunication cable (which connects the terminal equipment with a sensor) is a line leading beyond the building to a sensor in the field. As the building has lightning protection, the application of a lightning current arrester is necessary. Here the Blitzductor® CT types B or B . . . are suitable. No lightning protection, but MCR-cable leading beyond the building. Here the building with the terminal equipment to be protected has no lightning protection (Figure 5.8.2.1.2 b). Direct lightning strikes are not expected. Lightning current proof arresters type B or type B . . . are only necessary if the MCR-cable can be charged by lightning
Figure 5.8.2.1.2 a
Lightning protection, measuring and control cable crossing buildings
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Overvoltage protection of low voltage systems
Figure 5.8.2.1.2 b
•
•
No lightning protection, but measuring and control cable crossing buildings
strikes into neighbouring buildings (close-up strikes). If not, only Blitzductor® CT types M . . . are used. Lightning protection but no MCR-cable leading beyond the building. In this case (Figure 5.8.2.1.2 c) the MCR/telecommunication cabling does not have any lines leading beyond the building. Although the building has lightning protection no lightning partial current can be coupled into the considered part of the telecommunication system (the MCRsystem is in lightning protection zone 1). So, in this case surge arresters which are characterized as type M . . . in the Blitzductor® CT family are used. No lightning protection, no MCR-cable leading beyond the building. The building has no lightning protection and there is no MCR/ telecommunication cable leading beyond the building (Figure 5.8.2.1.2 d). To protect the MCR devices only surge arresters are necessary. Protective modules type M . . . are used.
SC B: Longitudinal or transverse surge protection. Types . . . E or . . . D? Longitudinal surges always arise between signal wires and earth, whereas transverse surges are generated between two signal wires. The interferences in the signal circuits are mostly longitudinal surges. This means, for the selection of protective devices, that usually fine protective devices are used between signal wires and earth, that is, the Blitzductor® CT, type . . . E. For certain inputs to equipment, such as isolating transformers, a fine protection between wire and earth is not necessary. Gas discharge arresters can protect against longitudinal surges. However, having a different impulse sparkover characteristic, gas discharge arresters can also
Components and protective devices: construction, effect and application
Figure 5.8.2.1.2 c
Lightning protection, but no measuring and control cable crossing buildings
Figure 5.8.2.1.2 d
No lightning protection, no measuring and control cable crossing buildings
225
cause transverse surges. That is why, in such a case, fine protection as offered by the Blitzductor® type . . . D is necessary between the signal wires. SC C: Which cases require Blitzductor® CT with output decoupling Types . . . E/C? Sometimes it is necessary to protect equipment inputs against longitudinal and transverse surges. The inputs of such electronic MCR equipment are usually already provided with protective circuits or have optocoupler inputs to separate the potential of the signal circuit from the
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Overvoltage protection of low voltage systems
internal circuit of the MCR equipment. This requires additional measures for decoupling the Blitzductor® CT from the input circuit of the equipment to be protected. Decoupling is guaranteed by additional decoupling elements between fine protective elements and output terminals of the Blitzductor® CT, type . . . E/C. SC D: Which cases require Blitzductor®s CT with higher cut-off frequencies? Types . . . D/HF? Like every transmission system the protective circuit of the Blitzductor® CT also has a sort of low-pass characteristic. An indication of the cutoff frequency (Section 5.8.2.1.1) shows from what frequency the amplitude of the signal to be transmitted will be attenuated by more than 3 dB. To keep the reaction of the Blitzductor® CT on the transmission system within the permissible limits, the cut-off frequency must be higher than the signal frequency of the signal circuit. The indication of the cut-off frequency is applicable for sinusoidal parameters. In the field of data transmission, however, there are mostly no sinusoidal signal forms. Therefore, it must be taken into account that the maximum data rate of the Blitzductor® CT is higher than the transmission rate of the signal circuit. On transmitting pulse shaped signals where the rising and the falling pulse edge is evaluated it must be considered that this edge changes within a certain period from ‘low’ (L) to ‘high’ (H) or from H to L. This time interval is important for the recognition of an edge and for the passing of a ‘prohibited area’. Thus, this signal needs a frequency bandwidth which is considerably wider than that necessary for the fundamental wave of this oscillation. The cut-off frequency of the protective device must therefore be levelled correspondingly high. A rule of thumb is that the cut-off frequency must not be lower than the fivefold fundamental wave frequency. Here the types BD/HF or MD/HF are necessary. SC E: What about the nominal current IN of the Blitzductor® CT? Owing to the electrical characteristics of the components used in the protective circuit of the Blitzductor® CT the signal current which can be transmitted over this protective device is limited. This means for the application that the nominal current IN of the Blitzductor® CT must be higher than (or equal to) the operating current of the MCR system. SC F: What about the nominal voltage UN of the Blitzductor® CT? The nominal voltage UN of the Blitzductor® CT must be higher than the maximum arising operating voltage of the MCR circuit so that the protective device will not show any limiting effect under normal conditions. The maximum operating voltage to be expected in a signal circuit usually
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can be compared with the nominal voltage of the transmission system (under consideration of tolerances). In the case of signal circuit current loops (e.g., 0–20 mA) the open circuit voltage of the system can be rated as the maximum possible operating voltage. SC G: To what do the voltage indications refer: wire/wire or wire/earth? Signal supply in MCR circuits can be symmetrical or asymmetrical. On the one hand, the operating voltage of the system can be indicated as wire/wire voltage and, on the other hand, as wire/earth voltage. This must be considered on selecting the protective device Blitzductor® CT. For different circuits of the Blitzductor® CT fine protective elements different nominal voltages are indicated. The different relativities of the nominal voltages of the Blitzductor® CT modules have been explained in Section 5.8.2.1.1. SC H: For what are the series impedance data of the Blitzductor® CT? For the coordination of the protective elements decoupling impedances are installed into the Blitzductor® CT. Being directly in the signal circuit they can influence it. Especially in current loops (0 . . . 20 mA, 4 . . . 20 mA) the installation of Blitzductor® CT can cause the maximum permissible ohmic resistance of the signal circuit to be exceeded, a fact that must be clarified before installation. SC I: What about the application of the Blitzductor® CT-coordination characteristics (KK)? For equipment used in different electromagnetic environmental conditions, IEC 61000-4-5/EN 61000-4-5 specifies different test severity levels regarding the immunity against impulse shaped interferences. The test severity runs from level 1 to 4, severity level 1 claiming the lowest immunity (to the equipment to be protected) and level 4 the highest. As described in section 5.8.2.1.1 this means that the ‘let-through energy’ related to the Blitzductor® CT protection level must be lower than the immunity level of the equipment to be protected. By means of the Blitzductor® CT coordination characteristics (KK) a coordinated application of the Blitzductor® CT for the protection of programmable controllers is possible. If, for example, a programmable controller has been tested according to test severity level 1, the coordinated Blitzductor® CT only must have a maximum ‘let-through energy’ which corresponds to this interference level, thus it must have output characteristic 1. In practice, this means that severity level 4 tested programmable controllers can work interference-free if the Blitzductor® CT output has a protection level corresponding to test severity degree 1, 2, 3 or 4. Thus, it is very easy for the user to select suitable protective devices.
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SC J: Single or multistage protection. Types B and M . . . or only type B . . . ? Depending on the infrastructure of the building and the protection requirements of the concept of lightning protection zones it may be necessary that lightning and surge arresters are either installed spatially separated or in one position in the system (Figure 5.8.2.1.2 e). In the first case, the application of the Blitzductor® CT with protective module type B as a lightning current arrester as well as Blitzductor® CT protective module type M . . . as a surge arrester is necessary. In the second case lightning and surge protective measures shall be carried out in one position in the system; here the combined arrester Blitzductor® CT, type B . . . is applied.
Sources DEHN + SÖHNE: ‘Selection and installation of surge protective devices. Type Blitzductor® CT for protection of control and instrumentation systems acc. to IEC 61312-1’. DS 656/E August 1997 IEC 61000-4-5:1995: ‘Electromagnetic compatibility (EMC) – Part 4: Testing and measurement techniques (Section 5): Surge immunity test’. International Electrotechnical Commission, Geneva 1995
5.8.2.1.3 Blitzductor® CT: Examples of application. The following three examples of application show the selection of protective devices of the Blitzductor® CT family by means of the above described selection criteria (SC) A to J. The result of every single step of the selection is entered into a selection table under the column ‘single result’. The column ‘con-
Figure 5.8.2.1.2 e
Single and multistep protection
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secutive result’ then shows the influence of the particular single result on the consecutive selection result. At the end of every selection table the final result ‘The applicable Blitzductor® CT’ can be read.
Source DEHN + SÖHNE: ‘Selection and installation of surge protective devices. Type Blitzductor® CT for protection of control and instrumentation systems acc. to IEC 61312-1. DS 656/E/897
5.8.2.1.3.1 Lightning/surge protection for electronic vehicle weighbridges. Electronic vehicle weighbridges (for road and railway vehicles) are susceptible to incoupled surges due to the large distance between measuring sensor and the evaluation unit (especially at outdoor weighing machines). The damaging of components and the failure of the whole weighing system is a considerable impairment to a commercial enterprise. Some examples concerning how to select lightning surge protective devices for a weighing machine are now described. The electrical measurement of the non-electric parameters of force or mass is made indirectly by measuring electrical resistance. Strain gauges are used as ohmic transducer elements. These consist of resistance foils which are coated on the carrier mostly in ‘meanders’. The extension or compression of a strain gauge along the printed conductor causes a change in length and cross section of the printed conductors and thus a change in their ohmic resistance. Strain gauges are coated onto a deforming carrier in such a way that two strain gauges are in extension and two strain gauges are in compression. These gauges are coupled in a bridge so that strain gauges stressed in equal directions are located in diametrically opposing branches (Figure 5.8.2.1.3.1 a). This bridge will be supplied with a DC voltage.
Figure 5.8.2.1.3.1 a
Basic diagram: Electronic weighbridge system
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Overvoltage protection of low voltage systems
The resistance changes due to the extension are very small and regarding the limits concerning the thermal stressing of the strain gauges, the bridge diagonal voltage is only some millivolts within the nominal range of the bridge supply voltage of up to 12 V. To compensate for the influence of temperature and voltage drop on long connecting cables two compensating leads are run from the measuring sensor to the evaluation unit. This procedure is called the six-conductor technique. Table 5.8.2.1.3.1 a indicates the single results which are due to the
Table 5.8.2.1.3.1 a
Lighting/surge protection for electronic vehicle weighbridges: Selection procedure (SC: selection criterion)
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individual selection criteria SC (A to J) and the consecutive selection results as well as the final result: Blitzductor® CT, type BE 12 (for circuit, see Figure 5.8.2.1.3.1 b; for technical data, see Table 5.8.2.1.3.1 b). Figure 5.8.2.1.3.1 c shows the protection of an electronic weighing machine (with four measuring sensors) using Blitzductor® CT type BE 12. To standardize the equipment of the weighing system with protective devices, all measuring leads have been equipped with the same Blitzductor® CT types. It is proven practice to assign one protector each to the wire pairs for supply, compensation and measuring. On subsequent installation of protective devices into the measuring circuits, the weighing system must be re-calibrated. The Blitzductor® CT may only be installed into the measuring circuits of weighing systems to be calibrated if the protective devices have been confirmed by an authorized testing institute of the EC (e.g., the Federal Institute of Technical Engineering) together with the weighing machine. Lightning and surge protection of the 230 V supply of the weighing system is also necessary (for reasons of clarity this is not shown in the Figure 5.8.2.1.3.1 c).
Source DEHN + SÖHNE: ‘Selection and installation of surge protective devices. Type Blitzductor® CT for protection of control and instrumentation systems acc. to IEC 61312–1’. DS 656/E Aug. 1997
5.8.2.1.3.2 Lightning/surge protection for field-bus systems. Because of the automation process individual sections of production are interconnected by field-bus systems. Automation systems can be established with field-buses where decentral control systems are also included (Figure 5.8.2.1.3.2 a). Such systems are especially endangered by incoupled surges due to their spatial extension. If such field-bus system
Figure 5.8.2.1.3.1 b
Blitzductor® CT, type BE 12: Basic circuit diagram
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Overvoltage protection of low voltage systems
Table 5.8.2.1.3.1 b
Blitzductor® CT-type BE 12: Technical data
components are damaged there is relatively little hardware loss but a great deal of production loss due to the subsequent production standstill. The field-bus is a serial bus system having technical and functional characteristics for the networking of automation units at the lower and medium performance level. Well-known bus systems for automation technology include: Profibus®, Interbus-S, DIN Messbus, D-Net, Suconet, Bit-Bus, SINEC L1, PLS-Net, SINEC L2 DP and CANbus.
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Figure 5.8.2.1.3.1 c
Suppressor circuit for electronic weighbridge system with four measuring sensors
Figure 5.8.2.1.3.2 a
Basic diagram: Field-bus system
In most cases it is a serial interface (type RS 485) which is connected to a combined transmitting and receiving line (party-line). The transmission process of the RS 485 interface makes a difference evaluation of the wire signal voltages. Owing to the twisting of the wires the bus line is insensitive to inductive incouplings between its wires (transverse surges). Thus, the surge threat for the RS 485 interface is in the transient potential increase of the signal wires to earth (longitudinal surges). Table 5.8.2.1.3.2 a again shows the step-by-step procedure to determine the suitable protective devices. This is a two-stage protective system
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Overvoltage protection of low voltage systems
Table 5.8.2.1.3.2 a
Lightning/surge protection for field-bus system: Selection procedure (SC: selection criterion)
out of the lightning current arrester Blitzductor® CT, type B 110 and surge arrester Blitzductor® CT, type MD/HF 5 (for circuits, see Figure 5.8.2.1.3.2 b; for technical data, see Table 5.8.2.1.3.2 b). Figure 5.8.2.1.3.2 c shows the protection of an actuator, distributed inputs and outputs, sensors and programmable controllers connecting field-bus systems with the selected Blitzductors. Lightning and surge protection of the 230 V supply is also necessary (but not shown in Figure 5.8.2.1.3.2 c for reasons of clarity).
Components and protective devices: construction, effect and application
Figure 5.8.2.1.3.2 b
Table 5.8.2.1.3.2 b
(a)
235
Figure 5.8.2.1.3.2 b (b) Blitzductor® CT, type MD/HF 5
Blitzductor® CT-types B 110 and MD/HF 5: Technical data
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Overvoltage protection of low voltage systems
Figure 5.8.2.1.3.2 c
Suppressor circuit for field-bus system
Source DEHN u. SÖHNE: ‘Selection and installation of surge protective devices. Type Blitzductor® CT for protection of control and instrumentation systems acc. to IEC 61312-1. DS 656/E Aug. 1997
5.8.2.1.3.3 Surge protection for electrical temperature measuring equipment. Electrical temperature measuring of media in technological processes is performed in all industrial fields. The areas of application can be very different: from food processing to chemical processes to the air-conditioning of buildings. Generally, there is a large distance between the location of the measuring sensor and the measured-data indicator or processing equipment. Into these long bonding lines surges can be incoupled which are not necessarily caused by atmospheric discharges. The following description contains a suggestion of how to protect a PT 100 standard resistance thermometer against surges. The building where the measuring equipment is installed has no lightning protection. The temperature is determined by measuring the electrical resistance. The resistance thermometer (PT 100) has a resistance value of 100 Ω at 0 °C. Depending on the temperature, this value changes by 0.4 Ω/K. To determine the temperature, a constant measuring current is impressed causing a voltage drop at the resistance thermometer which is proportional to the temperature. This measuring current is limited to 1 mA in order to avoid self-heating of the resistance thermometer. Thus, at the PT 100 there will be a voltage drop of 100 mV at 0 °C, which will be transmitted to the place of indication or evaluation (Figure 5.8.2.1.3.3 a).
Components and protective devices: construction, effect and application
Figure 5.8.2.1.3.3 a
237
Basic diagram: electrical temperature measuring equipment
An example of the different possible connection systems for a PT 100 measuring sensor is shown by the four-conductor connection in Figure 5.8.2.1.3.3 a. So, the influence of the conductor resistance and its temperature-sensitive fluctuations on the measuring result are excluded. The PT 100 sensor is supplied by an impressed current. Changes in the conductor resistance will be automatically compensated for by the adjustment of the supply voltage. There is a high-resistance pick-up at the sensor by the measuring transducer of the changing measuring voltage Um depending on the temperature of the measuring resistance. Table 5.8.2.1.3.3 a shows how to proceed step-by-step with the selection of suitable protective devices. For the Blitzductor® CT, type ME 5, surge arresters are necessary (for circuit, see Figure 5.8.2.1.3.3 b; for technical data, see Table 5.8.2.1.3.3 b). Figure 5.8.2.1.3.3 c shows the protection of electrical temperature measuring equipment. To standardize the equipment of the temperature measuring system with surge protective devices, supply and measuring lines are protected by the same Blitzductor® CT-types. It is proven practice to assign one protector each to the wire pairs for supply and for measurement. Surge protection of the 230 V supply for the PT 100 measuring transducer, as well as of the 4–20 mA current loop (beginning there), is also necessary but not shown in Figure 5.8.2.1.3.3 c for reasons of clarity.
Source DEHN + SÖHNE: ‘Selection and installation of surge protective devices. Type Blitzductor® CT for protection of control and instrumentation systems acc. to IEC 61312-1’. DS 656/E Aug. 1997
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Table 5.8.2.1.3.3 a
Surge protection for electrical temperature measuring equipment: Selection procedure (SC: selection criterion)
5.8.2.1.3.4 Blitzductor® CT applications: Further cases. Table 5.8.2.1.3.4 a lists further cases of application for different Blitzductor® CT-types. 5.8.2.1.4 Arresters for intrinsically safe measuring and control circuits and their application. In areas where gases, vapours, fogs or dusts are caused by treating or transporting inflammable material, which together with the air can form a dangerous explosive atmosphere, special explosion protection measures must be taken. To avoid the situation where the
Components and protective devices: construction, effect and application
Figure 5.8.2.1.3.3 b Table 5.8.2.1.3.3 b
Basic circuit diagram: Blitzductor® CT, type ME 5 Blitzductor® CT, type ME 5: Technical data
239
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Overvoltage protection of low voltage systems
Figure 5.8.2.1.3.3 c
Table 5.8.2.1.3.4 a
Suppressor circuit for electrical temperature measuring equipment
Examples for the use of Blitzductor® CT
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electrical operating facilities become the sources of ignition in explosive atmospheres these are designed to have different types of protection. One type of protection which is used worldwide in the measuring and control technique is Intrinsic Safety Ex(i). ‘Intrinsic safety’ protection is based on the principle of current and voltage limitation in a circuit. Power is kept at such a low level that neither by sparks nor by unpermissible surface heating of the electric components can the surrounding explosive atmosphere be ignited. Not only the voltage and current of the electric equipment but also the energy storing inductors and capacitors in the whole circuit must be limited to safe maximum values. Thus, for safe operation (e.g., a measuring and control circuit) neither a spark due to the opening and closing of the circuit (e.g., at switch contacts) nor a fault (e.g., a short circuit or an earth fault) will cause ignition. Furthermore, heat ignition by the equipment and lines in the intrinsically safe circuit must be eliminated both for the normal state as well for the possibility of a fault. Application of the ‘intrinsic safety’ type of protection, thus, is limited to relatively low-performance circuits. It is achieved by limiting the available energy in the circuit. In contrast to other types of protection, this limitation is not only to individual devices but to the whole circuit. This system is divided into ‘Ex-zones’ and, in general, this division depends on the probability and the permanence of an explosive atmosphere. Zones with dangerous explosive atmosphere due to gases, vapours and fog are ranked as Ex-zones 0 to 2 and those with dangerous explosive atmosphere due to dusts as Ex-zones 20, 21 and 22. Depending on how explosive the different materials are, there are explosions groups I, IIA, IIB and IIC for which the corresponding minimum ignition curves are specified. The ignition characteristics of the explosive material include a minimum ignition curve that indicates the maximum values for the operating voltage and operating current. Explosion group IIC contains the most explosive materials, such as hydrogen and acetylene. When heated, these gases have different ignition temperatures which are specified by classifying them according to temperatures (T1–T6). At the interface between Ex-area and non-Ex-area (safe area), safety barriers or measuring transformers with an Ex(i)-output circuit will be inserted for separation. The safety-technical maximum values of a safety barrier or a measuring transformer with Ex(i)-output circuit are specified by the test certificate of an authorized testing agency. These are, namely, (i) the maximum output voltage (U0), (ii) the maximum output current (I0), (iii) the maximum external inductance (L0) and (iv) the maximum external capacitance (C0). The planner/installer must examine in every single case whether these maximum values are met by the connected equipment in the intrinsically safe circuit (such as field equipment, cables and surge protective devices). Corresponding values are indicated on the type label of the approved equipment or in the prototype test certificate.
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Intrinsic safety protection entails all currents, potentials and electric energy storage mechanisms, but not externally incoupled overvoltages due to atmospheric discharges, which may arise in large industrial plants after direct, close-up and remote lightning strikes. In the case of direct or close-up lightning strikes the voltage drop causes a potential increase of some 10 to 100 kV at the earthing system. As a potential difference this affects all equipment connected at distant locations. Such potential differences will exceed the insulation resistance of the equipment. In the case of remote lightning strikes, overvoltages are generated in lines which will damage the inputs of electronic equipment as transverse voltage (voltage difference between the wires). Thus, as protection against lightning or surge hazards the relevant arresters must be installed. Figure 5.8.2.1.4 a shows the consideration of surge arresters in intrinsically safe measuring and control circuits. As an example of the Blitzductor® CT MD/Ex 24 (Figure 5.8.2.1.4 b) with a certificate from the Federal Institute for Physical Engineering (Physikalisch Technische Bundesanstalt PTB, Braunschweig), the specific selection criteria for this protective device will now be explained. This surge protective device has the equipment mark ‘Eex ia IIC T6’ which has the following meaning: (i)
Eex: The testing agency certifies the accordance of this electrical equipment with the harmonized European Standards EN 50 014 ‘Electrical Apparatus for Potentially Explosive Atmospheres. General Requirements’ and EN 50 020 ‘Intrinsic Safety i’.
Figure 5.8.2.1.4 a
Application of surge arresters in the intrinsically safe measuring and control circuit, calculation of L0 and C0
Components and protective devices: construction, effect and application
Figure 5.8.2.1.4 b (ii)
243
Blitzductor® CT, type MD/Ex24 (colour blue)
Regarding the safe current and voltage limitation there are two categories to be considered: Category ib specifies that in case of a fault in the intrinsically safe circuit the intrinsic safety must be preserved. Category ia requires that on the occurrence of two independent faults the intrinsic safety must still be preserved.
• •
The Blitzductor® CT MD/Ex 24 is assigned to category ia with its highest demands and so it may be installed also with other equipment which is in Exprotection zone 0 and 20. (iii) II C: Classification into explosion groups. Explosive gases, vapours and fogs are classified according to the spark energy necessary to ignite the most explosive mixture with air. Equipment is classified according to the gases with which it can be used. Group II applies for all fields of use, such as the chemical industry, coal and cereal processing, however not in underground mining. Danger of explosion is highest in group II C because it considers mixtures of lowest ignition energy.
• •
The certificate of the Blitzductor for explosion group II C therefore meets the highest demands for a hydrogen in air mixture. (iv) T6: Classification according to temperatures. In the case of a hot-surface ignition of an explosive atmosphere a material-typical minimum temperature is necessary. The ignition temperature is a material classification figure which characterizes the ignition reaction of the gases, vapours, or dusts at a hot surface. For economical reasons gases and vapours are classified according to temperatures. Temperature class T6 means that the maximum surface temperature of the component must not exceed 85 °C in operation as well as in the case of a fault and the ignition temperature of the gases
244
Overvoltage protection of low voltage systems and vapours must be higher than 85 °C. Thus, the T6 classification is the highest demand for the Blitzductor® CT.
In accordance with the PTB-certificate of conformity the following electrical parameters must be considered: external inductance (L ) and maximum external capacitance • Maximum (C ). Owing to the special component selection in the Blitzductor CT 0
®
0
• •
the internal inductance and capacitance values of the different individual components are negligible. Maximum input current (Ii). The highest permissible current which may be supplied through the terminal parts is 500 mA without cancelling the intrinsic safety. Maximum input voltage (Ui). The highest voltage with which the surge protective device Blitzductor® CT may be loaded is 26.8 V without cancelling the intrinsic safety.
Concerning the practical application of arresters in intrinsically safe circuits (Figure 5.8.2.1.4 e) the requirements for the insulation resistance need special care. The insulation between an intrinsically safe circuit and the equipment chassis or other parts which can be earthed should withstand the effective value of an AC test voltage being twice as high as that of the intrinsically safe circuit or 500 V (depending on which value is higher). Equipment having an insulation resistance ≥ 500 V AC is considered as earthed. Intrinsically safe equipment (e.g., underground lines, measuring transducers, formers, sensors etc.) usually has an insulation resistance of > 500 V AC. Intrinsically safe circuits must be earthed for safety reasons. They may also be earthed, if necessary, for reasons of function. This earthing may be realized only at one point by connection with the equipotential bonding. Surge protective devices having a DC operating voltage to earth < 500 V DC, provide an earth of the intrinsically safe circuit. An intrinsically safe circuit is considered as not earthed if the DC operating voltage of the protective device is > 500 V DC. The Blitzductor® CT, Type MD/Ex 24 meets this requirement. Figure 5.8.2.1.4 c shows how to use the Blitzductor® CT MD/Ex surge protective devices to protect a transducer and a sensor. In order not to worsen the arrester protective level due to voltage drop (of the interference current to be discharged), care must be taken of the consequent equipotential bonding between the equipment to be protected and the surge protective device. In Figure 5.8.2.1.4 c this is achieved by an additional equipotential line between the equipment and the Blitzductor® CT. Figure 5.8.2.1.4 d shows a special case of application. As a surge protective device in the Ex-area, the (ex-certified) Blitzductor® CT MD/Ex is used. As a surge protective device in the non-Ex-area, however, a (not Ex-
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Figure 5.8.2.1.4 c
Application of Blitzductor® CT, type MD/Ex in the intrinsically safe measuring and control circuit of an Exsystem
Figure 5.8.2.1.4 d
Application of different Blitzductor®s in an intrinsically safe circuit, which is partly in the Ex-area
certified) Blitzductor® CT, ME is used having a protection level between cores to earth/equipotential bonding of much less than 500 V. In the latter case this is necessary because the insulation resistance of the transducer is < 500 V AC.
Sources MÜLLER, K. P.: ‘Überspannungsschutz in eigensicheren MSR-Kreisen’. de (der elektromeister + deutsches elektrohandwerk), 1997, H. 20, pp. 1913–1916
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Overvoltage protection of low voltage systems
Figure 5.8.2.1.4 e
Blitzductor® CT, type MD/Ex for the protection of a pipeline valve station
EN 50 014: ‘Electrical apparatus for potentially explosive atmospheres. General requirements’ (VDE Verlag, GmbH, Berlin) March 1994 EN 50 020: ‘Electrical apparatus for potentially explosive atmospheres. Intrinsic safety “i” ’ (VDE Verlag, GmbH, Berlin) April 1996
5.8.2.1.5 Arresters for cathodic protection systems. Underground metal facilities (e.g., containers and piping) are subject to electrochemical corrosion, with the metals being the electrodes and the surrounding soil the electrolyte. A characteristic of the electrochemical corrosion is the dependence of the corrosion process on the electrodes’ potential (potential of metal in soil). If there is metal in the soil, positively charged ions enter into the soil and vice versa; also positive ions from the electrolyte (soil) are taken up by the electrode (metal). In this context we speak of the ‘dissolution pressure’ of the metal and the ‘osmotic pressure’ of the electrolyte. Depending on both pressures, either the positive ions of the buried metal facility are increasingly dissolved (thus it becomes negative with regard to the soil) or positive ions from the soil increasingly deposit at the metal (then the metal facility becomes positive with regard to the soil). If buried facilities out of different metals are connected outside the soil (e.g., within the scope of equipotential bonding) then current flows in the external circuit from the positive to the negative electrode; in the soil, however, from the negative to the positive electrode. So, the more negative metal facility delivers positive ions to the soil, thus becoming the anode of the created galvanic element with the consequence of being dissolved (corroded) as time passes. Such corrosion
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can be avoided by current supply where a mains-operated rectifier supplies a current over an anode through the soil into the endangered metal facility, thus becoming a corrosion protected cathode. Figure 5.8.2.1.5 a shows the basic diagram of such a cathodically protected system for a pipeline. The measuring sensor picks up the potential of the pipeline to the surrounding soil, initiating the optimal value of protective current at the adjustable rectifier. Cathodically protected systems can be endangered by surges due to lightning discharges and faults in high-voltage overhead lines or traction power supply (running in parallel to the pipeline). Protection is offered by (Figure 5.8.2.1.5 b) Blitzductor® KKS, type AD I for the impressedcurrent anode circuit, and Blitzductor® KKS, type APD for the measuring
Figure 5.8.2.1.5 a
Cathodic protection system: Basic design
Figure 5.8.2.1.5 b
Blitzductor® KKS, type APD
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Overvoltage protection of low voltage systems
sensor circuit. Technical data are provided in Table 5.8.2.1.5 a. Figure 5.8.2.1.5 c shows how these surge arresters are used. 5.8.2.1.6 Arresters in Euro-card format. Arresters in Euro-card format have an especially space-saving design (Figure 5.8.2.1.6 a). They contain a graded protective circuit as shown in Figure 5.8.2.1.6 b. Such protective cards can be inserted into individual enclosures (Figure 5.8.2.1.6 c), into 19″-racks (Figure 5.8.2.1.6 d) or into complete protective cabinets (Figures 5.8.2.1.6 e). 5.8.2.1.7 Arresters in LSA-Plus-technology. Information technology distribution boxes are often realized using LSA technology, a quickconnection system without stripping, soldering or screwing: By means of a special tool the wires are simply pressed into the contact slots of the LSA rails. The wire insulation will be cut automatically and the copper core will be pushed between two spring-loaded contact tags. At the same time the tool also cuts off unnecessary wire ends. Figure 5.8.2.1.7 a shows components of an LSA-Plus system by means of which it is possible to construct, for example, small terminal junction Table 5.8.2.1.5 a
Blitzductor® KKS, types AD I and APD: Technical data
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249
Figure 5.8.2.1.5 c
(a) Basic diagram
Figure 5.8.2.1.5 c
(b) Application of the Blitzductor® KKS in a corrosion protection cabinet
Figure 5.8.2.1.5 c
Protection of a cathodic protection system with Blitzductor® KKS types APD and ADI
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Overvoltage protection of low voltage systems
Figure 5.8.2.1.6 b Circuit of the arrester shown in Figure 5.8.2.6 a (shown for two single wires)
Figure 5.8.2.1.6 a unit design
16 pole arrester in drawout-
Figure 5.8.2.1.6 c
Protective cards in aluminium housing for wall mounting
Figure 5.8.2.1.6 d
19″-drawout-unit housing for protective cards
Components and protective devices: construction, effect and application
Figure 5.8.2.1.6 e
251
Arresters in Eurocard design, mounted in a protective cabinet
boxes with the same economy as large distribution boxes or mains distribution frames with more than 10 000 connections. Terminal blocks and disconnection blocks are to be placed on terminal strips: the terminal blocks the cable wires and the jumping wires are con• At nected at opposite contacts. Between these terminal contacts there are
•
pick-off contacts where, for example, surge protective modules can be plugged in. In contrast to the terminal block, the disconnection block is constructed so that a disconnection plug can interrupt the contacts between the cable wire and the jumper wire side which is necessary to include in a protective decoupling link.
Figure 5.8.2.1.7 b shows protective devices designed especially for the LSA-Plus system. The protection plugs for one balanced line (Figure 5.8.2.1.7 b, lower left), consisting of ‘coarse protection’, ‘decoupling unit’ and ‘fine protection’, contain series links and must therefore be plugged into the LSA disconnection block (Figure 5.8.2.1.7 c). There is one protection block each for 10 balanced lines (Figure 5.8.2.1.7 b top right) which will also be plugged into the disconnection block.
Source HASSE, P., and WIESINGER, J.: “EMV Blitz-Schutzzonen-Konzept’ (Pflaum Verlag; München: VDE Verlag, GmbH, Berlin/Offenbach) 1994
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Overvoltage protection of low voltage systems
Figure 5.8.2.1.7 a system
LSA-Plus
Figure 5.8.2.1.7 b system
Arresters for LSA-Plus
Figure 5.8.2.1.7 c
Connection of communication technology lines at the entry to lightning protection zone 1 of the water purification unit Frauenau/Lower Bavaria
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253
5.8.2.2 Combined protective devices for power supply inputs and information technology inputs Equipment and systems connected to power technical and information technology networks, forming their own lightning protection zone and where the line routing leads to wide induction loops (Figure 5.8.2.2 a), will be input-protected by surge arresters which are designed for the connection of power lines as well as for information technology lines. The principle of protection is to realize the equipotential bonding between the systems in the case of overvoltage directly at the inputs of the device or of the system (Figure 5.8.2.2 b). It is the task of the protective elements S1 and S2 to limit the transverse voltages between the
Figure 5.8.2.2 a
Danger to information technology equipment connected to two systems due to induced lightning overvoltages
Figure 5.8.2.2 b
Topology of a protector for equipment or systems at two networks
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Overvoltage protection of low voltage systems
conductors (‘differential mode protection’) and to lead the longitudinal currents from the conductors (‘common mode protection’) to the common equipotential bonding bar. Figure 5.8.2.2 b shows the equipment to be protected in shunt to the protective device. This guarantees that overvoltages between the power mains and the information technology mains are limited in such a way that the puncture voltage of the equipment between the inputs E1 and E2 will not be exceeded. Furthermore, it guarantees that the common-mode currents can be conducted from the power mains into the information technology mains and vice versa. Moreover, dangerous surges between the conductors of one system cannot arise. Figures 5.8.2.2 c and d show surge arresters for realizing such ‘protective bypasses’.
Source HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen Konzept’ (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach, 1994)
Figure 5.8.2.2 c Surge arrester for the power input and the aerial input of a TV set/radio receiver
Figure 5.8.2.2 d Surge arrester for the power input and the data input of a computer terminal
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5.8.2.3 Protective devices for data networks/systems In the following Sections protective devices for different data networks will be introduced which can be used as part of the concept of lightning protection zones at the building input (e.g., LPZ-interface 0A(0B)/1), in the active distributor (HUB), in the terminal block (e.g., LPZ-interface 1/2), or at the terminal equipment (e.g., LPZ-interface 2/3). 5.8.2.3.1 Protective devices for application-neutral cabling. The European Standard EN 50173 ‘Information technology – Generic cabling systems’ offers: generic universally applicable cabling system and an open market for • acabling components a flexible cabling scheme where modifications can be realized easily • and economically to building professionals for cabling installation before • instructions specific requirements are known (that means early in the initial plan-
•
ning stage of construction or renovation) a cabling system for industry and the standardization committees for network use supporting actual products and acting as a basis for future product development.
This European Standard defines a universal cabling system which can be used in places with one or several buildings. It treats cablings with symmetric copper cables and optical fibre cables. The universal cabling covers a wide range of services including speech, data, text, still and moving pictures. Generic cabling consists of the following functional elements: distributor (CD) • campus primary • building cable (BD) • secondarydistributor cable • floor distributor (FD) • tertiary cable • cable distribution cabinet (alternatively) • information technology terminal. • Groups of these functional elements are connected to partial systems of the cabling. A universal cabling system consists of three partial systems: (i) primary, (ii) secondary and (iii) tertiary cabling. Together these partial systems form a universal cabling structure as shown in Figure 5.8.2.3.1 a. By means of distribution boards any mains topologies such as bus, radial and annular topologies can be achieved.
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Overvoltage protection of low voltage systems
Figure 5.8.2.3.1 a
Structure of generic cabling
(i)
The ‘primary cabling’ partial system goes from the campus distributor to the building distributor(s) which are usually in different buildings. It contains any primary cables, their first points of contact (at the campus and the building distributors) and the distribution facilities in the campus distributor. (ii) One partial system of the ‘secondary cabling’ goes from the building distributor(s) to the floor distributor(s). That partial system contains the secondary cables, their mechanical points of connection (at the building and floor distributors) and the distribution facilities in the building distributor. (iii) The ‘tertiary cabling’ partial system goes from the floor distributor to the connected information technology terminal(s). That partial system contains the tertiary cables, their (mechanical) points of connection at the floor distributor, the distribution facility in the floor distributor and the information technology terminals.
The equipment terminal cabling connects the information technology terminal with the terminal equipment. It is carried out according to local requirements and is therefore not covered by the range of application of this European Standard. Between the campus and building distributor optical fibre cables are usually used as data lines. So, no arrester from the field side is needed. The star couplers for distributing the optical fibre cables, however, are powered by 230 V and so arresters for the power engineering system (chapter 5.8.1) may be necessary. The secondary (building distributor to floor distributor) and tertiary connections (between floor distributor and terminal equipment) are often symmetric cables (e.g., twisted pair-cables). Cable lengths (max. 500 or 90 m) (Figure 5.8.2.3.1 b), where high longitudinal voltages can be induced when lightning strikes the building, would overload a HUB insulation strength or that of a network card in the terminal equipment. Therefore, surge protection measures must be carried out to protect both
Components and protective devices: construction, effect and application
Figure 5.8.2.3.1 b
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Application-neutral cabling systems
building/floor distributors (HUB) as well as telecommunication outlets (terminal equipment). Protective devices used for the above purpose are specified according to the type of network. Usually, the following types of networks apply: Ring • Token Ethernet 10 Base T • Fast Ethernet 100 Base TX. • Figure 5.8.2.3.1 c shows where the protective devices can be used: HUB and patchpanel a NET-Protector with surge protective • Between modules 4 TP (Figure 5.8.2.3.1 d, Table 5.8.2.3.1 a) is installed (Figure
•
5.8.2.3.1 e). At the terminal equipment a surge arrester, type ÜGKF/RJ45 4TP (Figure 5.8.2.3.1 f, Table 5.8.2.3.1 b) can be used, where all four core pairs are protected which provides a completely neutral application. However, it must be taken into account that the power input of the terminal equipment is also protected. The combined surge protective device DATA-Protector (Figure 5.8.2.3.1 g, Table 5.8.2.3.1 c), for example, can be used, or (as shown in Figure 5.8.2.3.1 h) surge arresters type ÜGKF/RJ45 for the data input and type SF-Protector (cf. Section 5.8.1.4 b, Figure 5.8.1.4 b) for the power input.
Sources EN 50173: ‘Information technology. Generic cabling systems’ (Beuth Verlag, GmbH, Berlin) Nov. 1995 DEHN + SÖHNE: ‘Surge protection: Safety for your data networks. Advice and equipment for optimized system solutions’. DS647 Oct.1996 DEHN + SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998
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Overvoltage protection of low voltage systems
Figure 5.8.2.3.1 c
Protectors in an application-neutral cabling system
Figure 5.8.2.3.1 d
NET-protector
Figure 5.8.2.3.1 e
NET-protector between HUB and Patchpanel
Components and protective devices: construction, effect and application
Figure 5.8.2.3.1 f (a) Surge arrester, type ÜGKF/RJ45 4TP Table 5.8.2.3.1 a
259
Figure 5.8.2.3.1 f (b) Basic circuit diagram: ÜGKF/ RJ45 4TP
NET-Protector for floor distribution boards (HUB) and other network components in 19″ modular packaging system
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Overvoltage protection of low voltage systems
Table 5.8.2.3.1 b
Surge arrester, type ÜGKF/RJ45 4TP: Technical data
Figure 5.8.2.3.1 g (a) Combined surge protector DATAProtector RJ45 4TP
Figure 5.8.2.3.1 g (b) Basic circuit diagram
Components and protective devices: construction, effect and application Table 5.8.2.3.1 c
261
Combined surge protective device DATA-protector RJ 45 4TP: Technical data
Figure 5.8.2.3.1 h Surge arresters, type KF/RJ45 and SF protector protect terminal
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Overvoltage protection of low voltage systems
5.8.2.3.2 Protective devices for token ring cabling. For token ring cabling the systems are connected in the ring topology and communicate according to the methods specified in IEEE 802.5. As floor distributors, mostly controllable ring distributors are used to perform the network control of the different terminal equipment and the signal amplification. Long cables present no problems. The maximum data transmission rate is 16 Mbps. (A Herm–Aphrodite plug, also known as an IVS connector, serves as the connector; it serves as both a plug and socket.) Figure 5.8.2.3.2 a shows the principle of token ring cabling and where the necessary protective devices should be installed. At the interface of lightning protection zones 0A/1 (cable input at the building) lightning current arrester type TR8 (Figure 5.8.2.3.2 b,
Figure 5.8.2.3.2 a
Protectors in token ring cabling
Figure 5.8.2.3.2 b (b) Basic circuit diagram
Figure 5.8.2.3.2 b
(a) Lightning current arrester, type TR8 (surface housing) for two token ring lines
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263
Table 5.8.2.3.2 a) is used. A type FS HA surge arrester (Figure 5.8.2.3.2 c, Table 5.8.2.3 a), which should be mounted at the rearside of the floor distributor between data line and front plate as shown in Figure 5.8.2.3.2 d, protects the floor distributor (interface lightning protection zones 1 and 2). The surge arrester FS HA is a pluggable Herm–Aphrodite connector (IVS plug) also usable to protect the terminal equipment (interface lightning protection zones 2/3) (Figure 5.8.2.3.2 e). Table 5.8.2.3.2 a
Lightning current arrester TR8 and surge arrester FS HA: Technical data
264
Overvoltage protection of low voltage systems
Figure 5.8.2.3.2 c (a) Surge arrester, type FS HA (b) Basic circuit diagram
Figure 5.8.2.3.2 d
Figure 5.8.2.3.2 d (a) Ring line distributor of a token ring network
(b) Basic diagram
Components and protective devices: construction, effect and application
Figure 5.8.2.3.2 d
265
(c) Detail
Figure 5.8.2.3.2 d
Application of the FS HA surge arrester
Figure 5.8.2.3.2 e
Terminal with surge protectors: (energy side) type SFProtector; (data side) type FS HA
Sources IEEE Std 802 (Revision of ANSI/IEEE Std 802.5–1985): ‘Local area networks: Token ring access method and physical layer specifications’ (IEEE, New York, May 1989) DEHN u. SÖHNE: ‘Surge protection: Safety for your data networks. Advice and equipment for optimized system solutions’ DS647 Oct. 1996 DEHN u. SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998
5.8.2.3.3 Protective devices for Ethernet twisted pair cabling. For highperformance PC networks the twisted pair cabling system is used. Two types of cabling are specified: Ethernet 10 Base T and Fast Ethernet 100 Base TX. The structure of Ethernet 10 Base T is a ‘twisted pair’ cabling having
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Overvoltage protection of low voltage systems
a tree topology with cable lengths up to 100 m. The terminal equipment communicating by the transmission method is specified in IEEE 802.3. Bonding elements are RJ45 connectors. HUBs located in floor distributors are designed to support network management and the repeater function. The data transmission rate of the system is 10 Mbps. Fast Ethernet 100 Base TX was developed from Ethernet 10 Base T. With a higher data transmission rate of 100 Mbps this system continuously meets the growing requirements of data technology. The topology connectors and pin assignments are the same as those of the Ethernet 10 Base T. Owing to the active components in the floor distributor, large networks with widespread cabling systems can be realized. Figure 5.8.2.3.3 a is a proposal for how to protect an Ethernet ‘twisted pair’ cabling. The floor distributor (HUB) is protected by the NET-Protector 4 TP introduced in section 5.8.2.3.1 (Figure 5.8.2.3.1 d). This surge protective device is suitable for both Ethernet 10 Base T and Fast Ethernet 100 Base TX and fits the universal cabling as specified in EN 50173, class D (cat. 5). To protect the data input of the terminal equipment, surge protected data socket outlets DSM-RJ45–10 Base T with shielded RJ45-sockets (Figure 5.8.2.3.3 b, Table 5.8.2.3.3 a) can be used. HUB and terminal equipment can also be protected by the pluggable surge arrester ÜGKF/ RJ45 4TP (Figure 5.8.2.3.1 f, Table 5.8.2.3.1 b), as shown in Figure 5.8.2.3.3 c. Data and power input of the terminal equipment can be commonly provided with the combined surge protective device DATAProtector RJ45 4TP (Figure 5.8.2.3.1 g, Table 5.8.2.3.1 c).
Figure 5.8.2.3.3 a
Protectors in Ethernet twisted-pair cabling
Components and protective devices: construction, effect and application
Figure 5.8.2.3.3 b (a) Data socket outlet (with surge arrester) DSMRJ45-10 Base T protects data input of the terminal
Figure 5.8.2.3.3 b (b) DSM-RJ4510 Base T
267
Figure 5.8.2.3.3 b (c) Basic circuit diagram
Sources ANSI/IEEE 802 Edition: ‘Information technology – Telecommunications and information exchange between systems – Local and metropolitan area networks – Specific requirements. Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications’ (IEEE, New York, March 1996) EN 50173:1995-11: ‘Informationstechnik. Anwendungsneutrale Verkabelungssysteme’. Deutsche Fassung EN 50173 (Beuth Verlag GmbH, Berlin, 1995) DEHN u. SÖHNE: ‘Surge protection: Safety for your data networks. Advice and equipment for optimized system solutions’. DS647 Oct. 1996 DEHN u. SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998
5.8.2.3.4 Protective devices for Ethernet coax-cabling. Coaxial cabling systems do not require floor distributors and additional amplifiers. Two different types of coaxial Ethernet networks are distinguished: Thickwire according to IEEE 802.3, 10 Base 5, also called • Ethernet ‘Yellow Cable’. Thinwire according to IEEE 802.3, 10 Base 2, also called • Ethernet ‘Cheaper Net’. Their data transmission rate is 10 Mbps. The yellow coated ‘Ethernet Thickwire’ cable (rigid inner conductor, four shielding layers) has excellent electrical characteristics and can have a segment length up to 500 m. Connections to the cable segment are possible by means of a transmission/receiver unit (transceiver). Transceivers are connected by N-connectors or crimp snap-in connectors to the coaxial bus cable. It is possible to connect up to 100 transceiver stations in a 500 m segment. Up to 50 m long cable sets connect transceivers and stations. These sets are also called ‘drop-cables’.
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Overvoltage protection of low voltage systems
Table 5.8.2.3.3 a
Surge arrester DSM-RJ45–10 Base T: Technical data
By contrast ‘Ethernet Thinwire’ cable only has a shield and singlestranded conductor which is shielded by an outer wire fabric and so it is much more flexible than the ‘Ethernet Thickwire’ cable. The segment length of the thin Ethernet cable, however, is limited to 185 m with only 30 connections to be made at one cable segment. External transceivers are not necessary for these connections, but BNC-T connectors or
Components and protective devices: construction, effect and application
Figure 5.8.2.3.3 c
269
Compact-HUB and terminal are protected by type ÜGKF/RJ45 surge arresters. There is an SF-Protector to protect the power input of the terminal.
EAD outlets can be used as the Ethernet-connection cards in the stations already have integrated transceivers. The coaxial cables of both systems consist of wire and shield, the shield being earthed at one point (mostly at the server of the system). The shield is also a common return for the data transmission. Figure 5.8.2.3.4 a shows a proposal of how to protect a system. Ethernet Thickwire only allows two protectors per segment. These should be installed at the building entrance or at the floor entrance. Any number of protectors can be used with Ethernet Thinwire and it is recommended to protect every network card. The Ethernet Thickwire cable 10 base 5 in Figure 5.8.2.3.4 b (Table 5.8.2.3.4 a) is protected by a ÜGKF/N-L protector, whereas the ÜGKF/B-L surge arresters are used in the Ethernet Thinwire system 10 Base 2 in the Figure 5.8.2.3.4 c (Table 5.8.2.3.4 a).
Sources ANSI/IEEE 802 Edition: ‘Information technology – Telecommunications and information exchange between systems – Local and metropolitan area networks – Specific requirements. Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications’ (IEEE, New York, March 1996)
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Overvoltage protection of low voltage systems
Figure 5.8.2.3.4 a Table 5.8.2.3.4 a
Protectors in Ethernet coax-cabling Surge arresters, types ÜGKF/N-L and ÜGKF/B-L: Technical data
Components and protective devices: construction, effect and application
Figure 5.8.2.3.4 b
271
(a) Ethernet thickwire segment connected to the star coupler by an ÜGKF/N-L protector
Figure 5.8.2.3.4 b (b) Surge arrester, type ÜGKF/N-L with N-plug/socket
Figure 5.8.2.3.4 b (c) Basic circuit diagrams of the surge arresters ÜGKF/N-L and ÜGKF/ B-L (indirect shield-earthing possible by gas-filled surge arresters)
DEHN u. SÖHNE: ‘Surge protection: Safety for your data networks. Advice and equipment for optimized system solutions’. DS64 Oct.1996 DEHN u. SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998
5.8.2.3.5 Protective devices for standard cabling. Interfaces V.24 (RS 232 C), V.11 (RS 422) and Twinax for IBM hardware are often used to connect EDP systems such as terminals and printers. Interfaces RS 232 C (V.24) and RS 422 (V.11) are used with usual telephone cables in the startopology. Consider the following notes: (i)
V.24 (RS 232 C). This is a serial interface with a data transmission rate of up to 19.2 kbps. Standard bus drivers are able to support data transmission
272
Overvoltage protection of low voltage systems
Figure 5.8.2.3.4 c
(a) Application of surge arresters in the T-branch of an Ethernet-thinwire segment
Figure 5.8.2.3.4 c (b) Surge arrester ÜGKF/B-L to protect the network card in a workstation
(ii)
Figure 5.8.2.3.4 c (c) Surge arrester ÜGKF/B-L with BNC-plug/socket
lines of up to 15 m length, while special bus drivers are able to cover a distance of up to 300 m line length. By the use of an interface converter for RS 232 to TTY transmission, distances of more than 300 m can be reached. Usually 25-pole D-subminiature sockets and 9-pole connectors are used as connectors. V.11 (RS 422) This is a serial interface using two balanced lines for data transmission rates of up to 2 Mbps. Line lengths up to 1000 m are possible. The 15-pole D-subminiature socket is often used for mechanical connection.
Components and protective devices: construction, effect and application
273
(iii) Twinax cabling. The IBM standard is carried out with a shielded Twinax cable comprising a wire pair. In one Twinax line up to eight terminals can be connected in the bus topology. A data transmission rate of up to 1 Mbps is possible. The Twinax connector is used at the host computer (e.g., AS 400) as well as at the terminal.
Figure 5.8.2.3.5 a shows cabling protection with V.24(RS 232 C) and V.11(RS 422) interfaces. Figure 5.8.2.3.5 b shows the basic circuit diagram for data transmission in an IBM Twinax system. Figure 5.8.2.3.5 c shows the corresponding protection arrangement.
Figure 5.8.2.3.5 a
Protectors in a cabling system with V.24 (RS 232 C) and V.11 (RS 422) interfaces
Figure 5.8.2.3.5 b
Data transmission in the IBM Twinax system
274
Overvoltage protection of low voltage systems
Figure 5.8.2.3.5 c
Protectors in an IBM Twinax system
Figure 5.8.2.3.5 d (b) Surge arrester, type FS 25 E protects terminal input
Figure 5.8.2.3.5 d
(a) Surge arresters, type FS 25 E protect control unit (every terminal cable is protected)
Figure 5.8.2.3.5 d
(c) Surge arrester, type FS 25 E
Components and protective devices: construction, effect and application
275
The lightning current arrester Blitzductor® CT, type BE, 5 V, is installed to protect the V.24 (RS 232 C) / V.11 (RS 422) cabling at the building input. Surge arresters type FS 15 E (15-pole) or type FS 25 E (25-pole) protect the sockets (Figure 5.8.2.3.5 d, Table 5.8.2.3.5 a). If
Table 5.8.2.3.5 a
Surge arresters, types FS 25 E and FS 15 E: Technical data
276
Overvoltage protection of low voltage systems
there are TTY interface converters in such a system, then a type ÜSD-25TTY/B-KS surge arrester (Figure 5.8.2.3.5 e, Table 5.8.2.3.5 b) can be applied. The IBM Twinax system can be protected by type ÜGKF/Twinax surge arresters (Figure 5.8.2.3.5 f, Table 5.8.2.3.5 c).
Table 5.8.2.3.5 b
Surge arrester, type ÜSD-25-TTY/B–KS: Technical data
Components and protective devices: construction, effect and application Table 5.8.2.3.5 c
277
Surge arrester, type ÜGKF/Twinax: Technical data
Sources DEHN + SÖHNE: ‘Surge protection: Safety for your data networks. Advice and equipment for optimized system solutions’. DS647 Oct. 1996 DEHN + SÖHNE: ‘Surge protection. Main catalogue UE’98 Ed’. DS570/E 1998
5.8.2.3.6 Protective devices for data telecontrol transmission by an ISDN base terminal. Different services are offered across common public networks using ISDN (‘integrated services digital network’). Voice
278
Overvoltage protection of low voltage systems
Figure 5.8.2.3.5 f (b) Basic circuit diagram Figure 5.8.2.3.5 e (a) Surge arrester, type ÜSD-25TTY/B-KS for TTY-interface
Figure 5.8.2.3.5 f
(a) Surge arrester, type ÜGKF/Twinax protects IBM-terminal
Figure 5.8.2.3.5 f (c) Basic circuit diagram Figure 5.8.2.3.5 f
(b) ÜGKF/Twinax
Components and protective devices: construction, effect and application
279
frequencies as well as data can be transmitted digitally using ISDN. The supply line of the digital local exchange is a balanced line. A network terminal (NT) is the transfer interface for the user. The terminal base has 2 B-channels with 64 kbps each and a D-channel with 16 kbps. The NT is supplied with interface Uk0, the user’s interface is S0. A four-line bus topology can be up to 150 m long, a direct connection from point to point can be up to 1000 m long. Digital terminal equipment such as telephones, faxes or extensions may be connected to this interface. Figure 5.8.2.3.6 a shows where to use what type of protector. When protective devices are installed before the NT (Uk0 interface), the requirements of the telecommunication companies are to be observed. The Blitzductor® CT, type B arrester described in section 5.8.2.1.1 is installed at the lightning protection zone interface 0A/1 (Figure 5.8.2.3.6 b, Table 5.8.2.1.3.2 b). At the user’s interface (So interface) of the NT the pluggable surge arrester ÜGKF/RJ45 ISDN S0 (Figures 5.8.2.3.6 c, Table 5.8.2.3.6 a) is installed. There are one or two-pole data sockets (with surge protection) DSM1 × RJ45 ISDN So or DSM-2 × RJ45 ISDN So for ISDN terminals (Figures 5.8.2.3.6 d, Table 5.8.2.3.6 b). Systems with LSA-PLUS-terminals are protected by surge arresters such as type DPL 10 F/ISDN So (Figure 5.8.2.3.6 e, Table 5.8.2.3.6 c).
Figure 5.8.2.3.6 a
Protectors for long-distance data transmission with an ISDNbase terminal
280
Overvoltage protection of low voltage systems
Figure 5.8.2.3.6 b Lightning current arrester Blitzductor® CT, type B
Figure 5.8.2.3.6 c RJ45 ISDN So
Figure 5.8.2.3.6 c (a) Surge arrester ÜGKF/RJ45 ISDN So on the user side of the NTBA
(b) Surge arrester ÜGKF/
Figure 5.8.2.3.6 c (c) Basic circuit diagram
Components and protective devices: construction, effect and application Table 5.8.2.3.6 a
Figure 5.8.2.3.6 d
281
Surge arrester, type ÜGKF/RJ45 ISDN So: Technical data
(a) Data socket outlet (with surge arrester) DSM–2 × RJ45 ISDN So protects ISDN terminals (Fax and telephone)
282
Overvoltage protection of low voltage systems
Figure 5.8.2.3.6 d
(b) Data socket outlets (with surge arresters) types DSM– 1 × RJ45 ISDN So and DSM-2 × RJ45 ISDN So
Figure 5.8.2.3.6 d
(c) Basic circuit diagrams
Figure 5.8.2.3.6 e (b) Basic circuit diagram
Figure 5.8.2.3.6 e (a) Surge protective block, type DPL 10F/ISDN So for 10 double wires to plug into LSA-PLUS disconnection block
Components and protective devices: construction, effect and application Table 5.8.2.3.6 b
283
Data socket outlets (with surge arresters), types DSM1 × RJ45 ISDN SO and DSM-2 × RJ45 ISDN So: Technical data
284
Overvoltage protection of low voltage systems
Table 5.8.2.3.6 c
Surge protective block, type DPL 10 F/ISDN So: Technical data
Sources DEHN + SÖHNE: ‘Surge protection: Safety for your data networks. Advice and equipment for optimized system solutions’. DS647 Oct. 1996 DEHN + SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998.
5.8.2.3.7 Protective devices for data telecontrol transmission by ISDN primary multiplex terminal. The primary multiplex terminal has 30 B channels with 64 kbps each and a D channel with 64 kbps. Data transmissions up to 2.048 Mbps can be carried out via a primary multiplex terminal. The NT is supplied with interface U2m; the user’s interface is S2m. Large
Components and protective devices: construction, effect and application
285
extension units or data lines with high data volumes are connected to this interface. The S2m interface is operated using normal telephone lines. Figure 5.8.2.3.7 a shows the basic arrangement of the protective devices. At the interface of lightning protection zone 0A/1 again a lightning current arrester Blitzductor® CT, type B (introduced in Section 5.8.2.1) (Figure 5.8.2.3.7 b) is used. In the user’s system surge arresters Blitzductor® CT, type MD/HF (also described in Section 5.8.2.1.1) (Figure 5.8.2.3.7 c, Table 5.8.2.3.7 a) are applied.
Figure 5.8.2.3.7 a
Protectors for long-distance data transmission with ISDNprimary–multiplex terminal equipment
Figure 5.8.2.3.7 b Lightning current arrester Blitzductor® CT, type B to protect the U2m interface
Figure 5.8.2.3.7 c Surge arrester Blitzductor® CT, type MD/HF ( for high-frequency applications)
286
Overvoltage protection of low voltage systems
Table 5.8.2.3.7 a
Surge arrester Blitzductor® CT-type MD/HF: Technical data
Sources DEHN + SÖHNE: ‘Surge protection: Safety for your data networks. Advice and equipment for optimized system solutions’. DS647 Oct. 1996 DEHN + SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998
5.8.2.3.8 Protective devices for data telecontrol transmission by analogue a/b-wire terminal. In industrial as well as in private sectors, analogue long-distance data transmission via modem is commonly used. The data transmission rate is determined by hardware components of the modem. The TAE system with N coding is specified by the German Telecom as a plug-in connector. The exchange lines as well as branch exchange lines are mostly carried via terminals blocks. The LSA-PLUS terminals
Components and protective devices: construction, effect and application
Figure 5.8.2.3.8 a
287
Protectors for long-distance data transmisssion with analogue a/b-wire connection
Figure 5.8.2.3.8.b circuit diagram
(b) Basic
Figure 5.8.2.3.8 b (a) Lightning current arrester, type DPL 10G in LSAPLUS technique for protection of 10 double wires
Figure 5.8.2.3.8 c (b) Surge arrester, type DPL 1F/ALD, 110 V
Figure 5.8.2.3.8 c (a) Surge arresters, type DPL 1F/ALD, 110 V, protect the rank distributor
Figure 5.8.2.3.8 c (c) Basic circuit diagram
288
Overvoltage protection of low voltage systems
described in Section 5.8.2.1.7 are widely used for this purpose. Terminal equipment is often connected via TAE sockets with F coding. Figure 5.8.2.3.8 a shows the arrangement of protective devices in such a system. Lightning current arresters (e.g. Blitzductor® CT, type B) (Figure 5.8.2.3.7 b) or DPL 10 G (at LSA-PLUS terminals) (Figure 5.8.2.3.8 b, Table 5.8.2.3.8 a) are installed at the interface of the lightning protection zones 0A/1 (line input of the lightning protected building). The lines at the disconnection block are protected by surge arresters DPL 1F/ALD, 110 V (Figure 5.8.2.3.8 c, Table 5.8.2.3.8 b). The telephones are connected to TEA sockets (with surge protection) DSM-TAE-3x6 NFN-PWM (Figure 5.8.2.3.8 d , Table 5.8.2.3.8 c). The modem is protected by a combined surge protective device, type FAX-Protector TAE/N (Figure 5.8.2.3.8 e, Table 5.8.2.3.8 d).
Table 5.8.2.3.8 a
Lightning current arrester, type DPL 10 G: Technical data
Components and protective devices: construction, effect and application Table 5.8.2.3.8 b
289
Surge arrester, type DPL 1 F/ALD, 110 V: Technical data
Figure 5.8.2.3.8 d (b) Basic circuit diagram Figure 5.8.2.3.8 d (a) TAE-socket outlet (with integrated surge arrester for a/b wires) type DSM-TAE-3 × 6 NFN–PWM with three TAE-sockets with N/F/N coding
290
Overvoltage protection of low voltage systems
Table 5.8.2.3.8 c
TAE socket outlet (with surge arrester), type DSM–TAE-3 × 6 NFN-PWM
Figure 5.8.2.3.8 e (a) Combined surge protector, type FAX-protector TAE/N protects a/b-wire-input and 230 V-energy supply of the modem
Components and protective devices: construction, effect and application
Figure 5.8.2.3.8 e (b) Combined surge protector, type FAX-protector TAE/N Table 5.8.2.3.8 d
Figure 5.8.2.3.8 e diagram
FAX-Protector TAE/N: Technical data
291
(c) Basic circuit
292
Overvoltage protection of low voltage systems
Sources DEHN + SÖHNE: ‘Surge protection: Safety for your data networks. Advice and equipment for optimized system solutions’. DS647 Oct. 1996 DEHN + SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998
Chapter 6
Application in practice: Some examples
Here are some practical examples of how the protective measures described are carried out and how the protective devices introduced are used in electrical systems with sensitive electronic equipment. These are also systems which were seriously interfered with or even damaged by lightning previously. Since protective measures were completed the well-targeted application of protective devices has been working troublefree for years, even during violent thunderstorms and direct lightning strikes. It is now over 20 years since the development of surge limiters for highly sensitive electronic systems was initiated. At that time structures were equipped with the new protective devices and with ‘lightning current counters’. Today, there is more than a decade of reliable information on the efficiency of these surge protective devices, including those systems that failed five times and more per year in the previously unprotected stage. A lightning/surge current counter which can also register the response of surge protective devices is shown in Figure 6 a. This is designed according to the current transformer principle (Figure 6 b) and registers surge currents with peak values exceeding 200 A. Such a counter can be installed directly into the down conductor of a lightning protection system (Figure 6 c) or the earth bonding line of a protective device without reducing the cross section. Often it is necessary to carry out surge voltage/surge current tests not only in the laboratory or during the production of protective devices but also in the field. Here the portable ‘hybrid generator’ shown in Figure 6 d has been proven. In the case of a short circuit it emits a standardized 8/20 μs surge current with a maximum peak value of 10 kA, whereas in open circuit it generates the standardized surge voltage wave 1.2/50 μs with a peak value up to 10 kV.
294
Overvoltage protection of low voltage systems
Figure 6 a
Lightning/surge current counter
Figure 6 b
Lightning/surge current counter: Layout and interior circuit
Figure 6 d
Figure 6 c
Portable hybrid generator
Lightning/surge current counter installed at a down conductor
Application in practice: Some examples
295
6.1 Industrial plants As explained in Section 4.1.1, the necessary protective measures and the required lightning protection levels for a particular industrial plant are determined by means of risk analysis as a first step. In a second step the lightning protection zones will be determined according to the management plan introduced in Section 4.1.3 (in accordance with IEC 61312–1) (Figure 6.1 a). Modern construction techniques using steel skeletons, reinforced concrete and often metal facings allow integration of these metal parts into the lightning protection system. If lightning protection matters have been considered during the construction planning stage, advantageous architectural solutions can often be found.
6.1.1 Fabrication hall A step-by-step procedure for a factory hall built of prefabricated concrete elements (Figure 6.1.1 a) follows: lines bonding the reinforcement of the foundation socket • Connection (for the hall pillars) with the reinforcement of the pillars and with a
• •
ring type earth electrode are laid around the hall (Figure 6.1.1 b). Reinforcement of the pillars is interconnected and the connection lines are brought out at the bottom and top (Figures 6.1.1 c and d). Figure 6.1.1 e shows a finished pillar with the brought out reinforcement basket connection, ready to be placed into the foundation socket.
Figure 6.1 a
Industrial plant: lightning protection levels = PL (acc. to a risk analysis) and lightning protection zones = LPZ (in accordance with the LEMP-management plant)
296
Overvoltage protection of low voltage systems
Figure 6.1.1 a
Factory hall made out of prefabricated concrete parts, where the metal reinforcements are integrated into the lightning protection system (total view)
reinforcement mats are interconnected by continuous steel wires • Floor (Figure 6.1.1 f ), brought out near the pillars for final connection with
• • •
the ring equipotential bonding bar (Figure 6.1.1 g). Reinforcement connection wires brought out on top of the pillars (Figure 6.1.1 h) are to be connected with the steel construction of the attic (Figures 6.1.1 i and j). All piping or lines entering the factory building (such as water, heating, oil, compressed air pipes or power, telephone, data and signal lines) enter through a reinforced cable duct (the reinforcement of which will be connected with the hall reinforcement) at a point where the lightning protection equipotential bonding will also be carried out. All foundation reinforcements will be included into the earthing system (Figure 6.1.1 k), the individual reinforcement mats being interconnected by a continuous wire and corresponding clamps (Figure 6.1.1 l). Earthing systems of individual buildings of the whole structure to be protected shall be interconnected to a meshed surface earthing (Figure 6.1.1 m).
6.1.2 Store and dispatch building In this example the building is a computer-controlled high-bay warehouse (Figure 6.1.2 a) with dispatch area (Figure 6.1.2 b), made out of reinforced concrete supports, reinforced prefabricated concrete wall elements and a metal roof (Figure 6.1.2 c). The following Figures show how lightning protection measures are realized during the progress of construction:
Application in practice: Some examples
Figure 6.1.1 b Foundation socket with brought out reinforcement connection wire
Figure 6.1.1 d
297
Figure 6.1.1 c Reinforcement basket of a hall pillar (lying down, during fabrication) with connection line
Detail of Figure 6.1.1 c Figure 6.1.1 e Finished hall pillar (lying) with brought out reinforcement connection line
Figure 6.1.1 f Continuously interconnected reinforcement mats of the floor
Figure 6.1.1 g Brought out connection wire of the reinforcement mats provided for later connection to the ring equipotential bonding bar
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Overvoltage protection of low voltage systems
Figure 6.1.1 i Connection of the reinforcement with the attic support construction
Figure 6.1.1 h Reinforcement connection wire brought out at the pillar head
Figure 6.1.1 k Foundation reinforcement is included in the earthing system
Figure 6.1.1 j Connection of the attic support construction
Figure 6.1.1 l Terminal to connect reinforcement mats with steel strip
of the foundations for the building supports are to be • Reinforcements interconnected and provided with connection wires to the outside
•
(Figure 6.1.2 d); the reinforcement baskets will then be interconnected. Steel reinforcements of the supports are to be continuously connected (Figure 6.1.2 e).
Application in practice: Some examples
Figure 6.1.1 m
Building earthings interconnected to a meshed surface earthing
Figure 6.1.2 a warehouse
High-bay
Figure 6.1.2 b
299
Dispatch area
of foundation and support are to be connected (Figure • Reinforcements 6.1.2 f ). reinforcements are to be connected with the metal roof con• Support struction by clamps made to carry lightning currents (Figures 6.1.2 g). • Steel reinforcements of the prefabricated wall elements for the
300
Overvoltage protection of low voltage systems
Figure 6.1.2 c
Dispatch building
Figure 6.1.2 d
Reinforcement baskets with brought out connection wires
• •
high-bay warehouse (lightning protection zone 2) are already continuously connected by the producer (for later shielding purposes) and are provided with fixed earthing terminals (at which the wall elements then will be interconnected) (Figures 6.1.2 h). Figure 6.1.2 i shows such interconnected wall elements. Reinforcement steel mats in the store floor are to be interconnected; connection wires (for the ring equipotential bonding bar) are brought out at the walls (Figure 6.1.2 j).
Application in practice: Some examples
Figure 6.1.2 e Continuously interconnected support reinforcement
Figure 6.1.2 g
301
Figure 6.1.2 f Reinforcement steels of foundation and support are connected
Connection of the support reinforcement with the metal roof construction
is the way to create in the building (lightning protection zone 1) a • This completely shielded room (lightning protection zone 2) for the com-
•
puter controlled high-bay warehouse. Metal piping for water, heating, and compressed air entering the building through a supply duct are to be included into the lightning protection equipotential bonding by pipe clamps (made to carry lightning currents) on entering lightning protection zone 1 (Figure 6.1.2 k).
302 Overvoltage protection of low voltage systems
Figure 6.1.2 h Continuous reinforcement steels of the wall elements are prepared for shielding purposes
Figure 6.1.2 i Reinforcements of two wall elements interconnected at brought out fixed earthing terminals
Figure 6.1.2 j Interconnection of the steel mats in the floor with brought out connecting lugs for ring equipotential bonding bar
lines are to be provided with lightning current arresters on • Power entering lightning protection zone 1 of the building (Figure 6.1.2 l). technology lines will be connected across the protective • Information cabinet shown in Figure 6.1.2 m on entering the building (lightning
•
protection zone 1). On entering the high-bay warehouse (lightning protection zone 2) all electric lines are to be provided with surge arresters in the distribution (outside at the store wall) (Figure 6.1.2 n).
6.1.3 Factory central heating The central heating system of a factory, shown in Figures 6.1.3 a, has two 20 m high metal chimneys the protected area of which (lightning
Application in practice: Some examples
303
Figure 6.1.2 l Lightning current arrester at the input of power lines into lightning protection zone 1 Figure 6.1.2 k Inclusion of metal pipings into the lightning protection equipotential bonding at the entry into lightning protection zone 1
Figure 6.1.2 m Information technology lines (e.g. telephone lines, fire-alarm lines, control lines) are taken over a protective cabinet at the building input
304
Overvoltage protection of low voltage systems
Figure 6.1.2 n
Electrical lines entering lightning protection zone 2 of the highbay warehouse are connected with surge arresters
protection level III, α = 45°) is not sufficient (as shown in the side view of Figure 6.1.3 a, C) to avoid direct lightning strikes into the central heating. Also in this example it will be demonstrated step-by-step how lightning/surge protection is going to be carried out for a central heating system with steel pillars, sheet steel walls and a metal roof construction. Consider the following: 6.1.3 b shows the reinforcement of the ground plate (all struc• Figure tural steel mats being interconnected) and the metal plate foundations
• • • •
for the tubular steel pillars which are to be interconnected for reasons of earthing and shielding. The tubular steel pillars serve as down conductors (Figure 6.1.3 c). Figure 6.1.3 d shows how the reinforcement baskets of the metal chimneys’ foundations are interconnected. The tubular steel of the chimneys is to be bonded with the foundation reinforcement (Figure 6.1.3 e) to serve as ‘air terminations/down conductor/earthing’. Metal roof and sheet steel wall elements are to be bonded with the tubular steel pillars and the metal roof-supporting construction, thus
Application in practice: Some examples
(a) External view
(c) Side view Figure 6.1.3 a
• • •
305
(b) Front view
(d) Internal view Central heating
serving as ‘air terminations, down conductors and shield’ (Figure 6.1.3 f) and forming an inside lightning protection zone 1. All metal aggregates are to be connected with the base reinforcement (as directly as possible) via preinstalled fixed earthing terminals (chapter 5.2, Figure 5.2 g) (Figure 6.1.3 g). Electrical lines, on entering lightning protection zone 1, are to be provided with lightning current arresters in the switchgear cabinet (Figure 6.1.3 h). Figure 6.1.3 i shows the electrical line protected by surge arresters on
306
Overvoltage protection of low voltage systems
Figure 6.1.3 c Steel tube supports connected with the ground plate reinforcement as down conductors Figure 6.1.3 b Continuous ground plate reinforcement and metal plate foundations
Figure 6.1.3 d Reinforcement baskets of the chimney foundations
Figure 6.1.3 f
Figure 6.1.3 e Metal chimneys connected with the foundation reinforcement
Metal roof and wall elements are interconnected
Application in practice: Some examples
Figure 6.1.3 g
307
Metal aggregates sets are connected as closely as possible with the ground reinforcement by fixed earthing terminals
Figure 6.1.3 h Lightning current arresters at the entry of electrical lines into lightning protection zone 1
Figure 6.1.3 i Surge arresters at the crossing of electrical lines from lightning protection zone 1 into lightning protection zone 2 (control cabinet)
entering the control cabinet of the central heating unit which is lightning protection zone 2.
6.1.4 Central computer The central computer (Figure 6.1.4 a) of the factory is in the office building and is used for accounting, book-keeping, operations scheduling,
308
Overvoltage protection of low voltage systems
Figure 6.1.4 a
Computer centre of a factory
material tracking, production control and stock control. A long failure of this computing centre (e.g., due to surges) would not only paralyse the automatic operating process but also would mean an immeasurable financial loss for the company. Data transfer occurs over a four-wire current loop 20 mA current interface. 25-pole D-subminiature plugs are used as terminal facilities. The office building has been structured according to the concept of lightning protection zones where the interfaces of incoming lines are treated accordingly at the lightning protection zone boundary 0/1. The computer room in the office building is designated as lightning protection zone 2, as described below. The power cable is connected to surge arresters at the boundary of lightning protection zone 1/2 (Figure 6.1.4 b). For the datalines, surge protected data socket-outlets are installed at this zone crossing. They are mechanically and electrically compatible with the computer interfaces. These socket-outlet type surge arresters have a front-side ‘protected output’. They are installed into a 19 inch protective cabinet where they offer the possibility to jump, thus this cabinet can also serve as a terminal block (Figures 6.1.4 c and 6.1.4 d).
Sources HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen-Konzept’ (Pflaum Verlag, München, VDE Verlag, Berlin/Offenbach, 1994)
Application in practice: Some examples
Figure 6.1.4 b
309
Connection of mains and data lines of a computer centre at the interfaces of lightning protection zones 1/ 2 with surge arresters
Figure 6.1.4 c Front view of the 19 ″-protective cabinet for data lines
Figure 6.1.4 d
Detail of Figure 6.1.4 c
HASSE, P.: ‘EMV- orientiertes Blitz-Schutzzonen-Konzept mit Beispielen aus der Praxis’. Aus: ‘Elektromagnetische Verträglichkeit’ (VDE Verlag, Berlin/ Offenbach, 1991), pp. 59–150
6.1.5 European installation bus (EIB) Just as with any other electrical lines the bus network will also be included in the lightning/surge protection measures, that is lightning current arresters will be installed at the boundary of lightning protection zone
310
Overvoltage protection of low voltage systems
0A/1 (Figure 6.1.5 a). For surge protection of the bus line (Figure 6.1.5 b) there is an EIB surge-arrester terminal (Figures 6.1.5 c, Table 6.1.5 a) which, for example, can be mounted in a switch box (as Figures 6.1.5 d show). Figures 6.1.5 e show further application of this bus surge arrester for protection of bus devices in a factory. Figure 6.1.5 f shows the comprehensive protection of EIB lines crossing several buildings.
Figure 6.1.5 a
Inclusion of the bus network into the lightning protection equipotential bonding (Source: ZVEI/ZVEH)
Figure 6.1.5 b
Application of surge arresters at bus devices
Figure 6.1.5 c BUStector
(a) EIB-surge arrester
Figure 6.1.5 c (b) Basic circuit diagram
Application in practice: Some examples Table 6.1.5 a
311
EIB-surge arrester BUStector: Technical data
Figure 6.1.5 d
(a) Basic diagram
Figure 6.1.5 d
(b) Practical execution
Figure 6.1.5 d
(a, b and c) Mounting of the EIB-surge arrester in a switch box (Source: ZVEI/ZVEH)
Figure 6.1.5 d
(c) Practical execution
312
Overvoltage protection of low voltage systems
Figure 6.1.5 e
(a) at the connector
Figure 6.1.5 e
(b) at the line coupler
Figure 6.1.5 e
(a and b) Mounting examples for EIB-surge arresters (Source: ZVEI/ZVEH)
Figure 6.1.5 f
Lightning/surge protection of factory buildings with EIB-systems
Application in practice: Some examples
313
6.1.6 Other bus systems Other bus systems are equally integrated in the lightning protection concept by lightning current and surge arresters. It must always be considered that the local surge protection of the bus components (e.g., in a local lightning protection zone) includes both the power lines and the bus lines (Figure 6.1.6 a). This is shown, for example, by the SIMATIC ET 100 bus system (interface RS 485) in Figure 6.1.6 b.
6.1.7 Fire and burglar alarm system Fire and burglar alarm systems need long conductor loops through buildings and structures, encountering a considerable danger (especially
Figure 6.1.6 a
Surge protection for mains supply and bus lines: (left) SPSprotector; (right) Blitzductor®
Figure 6.1.6 b
Surge protection for SIMATIC ET 100
314
Overvoltage protection of low voltage systems
to the central alarm) due to surges. The minimum interference immunity of such systems is standardized in EN 50 130, prescribing the selection of the arresters to be used. There are two kinds of examining principles for fire and burglar alarm systems: line technique. According to the closed-circuit principle every • DC signal line (which has several detectors) is continuously controlled.
•
If a detector gives an alarm, the corresponding signal line will be interrupted and thus the alarm is given in the central alarm. Here only the signal line can be identified: not, however, the signalling detector. Impulse line technique. Here the information of a signalling detector will be transmitted in digital signals. By means of the transmission protocol the signalling detector can be identified.
The lines, just as those for any other network in buildings and systems, must be included in the lightning/surge protection: ®
the boundary of lightning protection zone 0 /1 the Blitzductor • At CT, type BE, for example, is used for lines which cross several A
•
buildings (selected according to the operating voltage of the signal line). At the central alarm (which is mostly designed as the local zone of protection) all inputs and outputs (signal line inputs, optical/ acoustical signal line outputs) will be equipped, for example, with a suitable Blitzductor® CT, where it should be taken into account that the nominal current of these arresters (at system operation) is not exceeded. In case of nominal currents > 1 A, for example, the surge protection device DEHNrail with adequate nominal voltage should be used.
The Blitzductor® CT, type BD, 110 V, for example, is recommended to protect telecoms lines (for the self-dial device). The power supply line of the central alarm will be protected as usual by the lightning current arrester (e.g., DEHNport® , 250 V), decoupling element (e.g., in the case of insufficient line length, DEHNbridge) and surge arrester (e.g., DEHNguard®). Figure 6.1.7 a shows a typical fire alarm system in the DC line technique; here, also, are the necessary protective devices. Figure 6.1.7 b shows the protection of a burglar alarm system using the DC line technique. The surge protection for the lightning protection zone crossing 1/2 for the Siemens fire central alarm, type BMS, is shown in Figure 6.1.7 c and in Figure 6.1.7 d for the Siemens burglar central alarm, type IT. For both of these protection proposals it is pointed out that the Blitzductor®s
Application in practice: Some examples
Figure 6.1.7 a
Protection of a fire-alarm system using DC line-technique
Figure 6.1.7 b
Protection of a burglar alarm system using DC line-technique
315
CT, type ME/C, are energy coordinated with the protective device type, 8 P/G, recommended by Siemens for such systems (Figure 6.1.7 e).
Source EN 50130–4: ‘Alarm systems. Part 4: Electromagnetic compatibility – Product family standard: Immunity requirements for components of fire, intruder and social alarm systems’ (International Electrotechnical Commission, Geneva, 1995)
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Overvoltage protection of low voltage systems
Figure 6.1.7 c
(a) Surge protection of the SIEMENS fire-alarm system, type BMS
Figure 6.1.7 c
(b) Example for the surge protection of a fire-alarm system
6.1.8 Video control system Video systems are used in industrial plants for object monitoring and access control. Figure 6.1.8 a shows the basic structure of such systems. They are included in lightning/surge protection systems as described below: of the video camera must not be subject to direct lightning • Location (lightning protection zone 0 ): for example, at the outer façade of B
Application in practice: Some examples
317
Figure 6.1.7 d
Surge protection of the SIEMENS burglar alarm system, type IT
Figure 6.1.7 e
Energy coordinated application of Blitzductor® CT, type ME/C and SIEMENS ÜSS, type 8 P/G
•
the building in the protection zone of the air terminations of the building’s lightning protection system, or the camera mast will be provided with an air termination rod. The system cable between camera and terminal box will be run in the shaft of the metal mast. Connection between terminal box (or transmitter) and monitor (or receiver) can, for example, be realized by the existing telephone network (symmetric two-wire line) of the industrial plant, or there is a separate coaxial line network. As shown in Figure 6.1.8 b the choice of lightning and surge arresters will depend on the requirements (at the lightning protection zone interfaces).
318
Overvoltage protection of low voltage systems
Figure 6.1.8 a
Video-monitoring system: Basic construction
Figure 6.1.8 b
Protection for video-monitoring system
The protective devices ÜGK/B and ÜGKF/BNC, mentioned in Figure 6.1.8 b, are shown in Figures 6.1.8 c with their technical data being summarized in Tables 6.1.8 a and b. For surge protection of a video control centre where several monitoring lines arrive, the protective devices for the 19 inch case mounting, shown in Figure 6.1.8 c (c), can be used (technical data equal to ÜGKF/ BNC).
6.1.9 Radio paging system A radio paging system, as used in an industrial area, is shown in Figure 6.1.9 a. Note that: (i) the actuator, with microphone and selective call
Application in practice: Some examples
319
Figure 6.1.8 c (b)
Figure 6.1.8 c (a)
Figure 6.1.8 c (c) Figure 6.1.8 c
(a) Lightning current arrester ÜGK/B (b) Surge arrester ÜGKF/ BNC (c) Surge arrester ÜGKF/BNC III
generator, is in the control room or in the keeper’s lodge; (ii) one or two double wires transmit the signal to the amplifier which is installed together with the omni-directional antenna in the roof area of an exposed building; and (iii) the amplified signal will be led to the antenna by a coaxial cable.
320
Overvoltage protection of low voltage systems
Table 6.1.8 a
Arresters for video systems: Technical data
(a) Lightning current arrester, type ÜGK/B
Figure 6.1.9 a also shows what protective measures shall be taken: current arresters are to be used at the lines which are cross• Lightning ing several buildings. For example: Blitzductor®s CT, type BE (according to the signal voltage) for the signal line double wires; coaxial arresters, type ÜGK (according to the type BNC, N, or UHF attachment) for the aerial coaxial line; DEHNport® for the 230 V supply (such lightning current arresters certainly are installed anyhow, if there is a lightning protection system). and amplifier will be protected at the 230 V input by surge • Actuator arresters, for example, DEHNguard , type 275 (which must be suf®
ficiently decoupled from the lightning current arresters).
6.1.10 Electronic vehicle weighbridge As explained in the example in Section 5.8.2.1.3.1, electronic vehicle weighbridges are powered using the four or six-wire technique: that is, two wires each for the supply voltage, for measuring and for compensation purposes.
Application in practice: Some examples (b) Surge arrester ÜGKF/BNC
Figure 6.1.9 a
Protection of a radio/paging system
321
322
Overvoltage protection of low voltage systems
Earthing and equipotential bonding measures for the weighbridge (with the pressure gauges) are shown in Figure 6.1.10 a. Figure 6.1.10 b shows how the protective devices are to be used:
Figure 6.1.10 a
Earthing and equipotential bonding measures for a vehicle weighbridge
Figure 6.1.10 b
Protection of an electronic vehicle weighbridge
Application in practice: Some examples
323
®
There are lightning current arresters Blitzductor CT, type BE, 12 V, at • the voltage supply, the measuring and compensation lines as well as at
• • •
the weighbridges and also at the evaluating electronics. Data transfer between evaluating electronics and large-digital display usually travels by symmetric interfaces. For example, V.11 (RS 422), thus Blitzductor® CT, type BE/C, 12 V, is used here. Control and monitoring of the weighing system in this example is realized by a personal computer (PC) having the asymmetric interface V.24 (RS 232). A type FS 25 E surge arrester protects this input to the evaluating electronics (since the PC is in the same building). The 230 V input of the evaluating electronics will be protected by surge arresters DEHNguard®, type 275 (since this line is already provided with a lightning current arrester, for example, DEHNport® at the building input).
6.2 Peak-load power station Using the example of the peak-load power station St. Veit of the Allgäuer Überlandwerk (AÜW) in Kempten it can be demonstrated how new buildings with electronic equipment already in the existing structures can obtain the best protection according to the lightning protection zone concept, and how these measures are made compatible with those already existing. A new engine hall with gas turbines has been joined to the engine hall with diesel generators and the lightning protection system has been integrated into the comprehensive lightning protection concept (Figure 6.2 a). The volume to be protected is defined as lightning protection zone 1 and comprises: the engine hall of the gas turbines the four underground gas tanks with the tank domes and the gas pipelines the external gas distribution station the corresponding connection routes with power cables and telecommunication cables. The transition from lightning protection zone 0 to lightning protection zone 1 shall be explained in detail by considering the construction of the engine hall. The flat roof and the façades consist of usual reinforced concrete elements with welded reinforcement (Figure 6.2 b). At the four corners of the prefabricated concrete elements there are threaded bushings which are welded to the reinforcement. At these bushings the individual concrete elements can be bonded (Figure 6.2 d). The defined down conduction of the lightning protection system from the roof to the foundations has been realized here by additional round steel in the concrete pillars. Additional bonding points are provided to connect the
• • • •
324
Overvoltage protection of low voltage systems
Figure 6.2 a
General plan of the peak-load power station
Figure 6.2 b Steel reinforcement of the prefabricated concrete parts
Figure 6.2 c Threaded bushing welded to the reinforcement
Application in practice: Some examples
325
reinforcement of the façade elements to down conductors. The wall side adjoining the already existing engine hall with the diesel generators has been covered by continuous wire netting to guarantee a closed, electromagnetic shield. In the floor of the engine hall a net of strip iron is welded to the reinforcement and bonded with the reinforcement of the cartridge-type foundations (Figure 6.2 e). By these simple and rather favourable measures it was possible to obtain an appreciable basic shielding of the engine hall interior against the electromagnetic field from a lightning discharge. shielded cables have been used inside the volume to protect in • Only lightning protection zone 1, thus leading to a further reduction in
existing residual fields of interference for the electrical lines. All shielded cables from the engine hall area are run to the information technology cabinets, realized using closed sheet metal boxes, of the directly neighbouring control room. Inside the information technology cabinets and the connected cables a lightning protection zone 2 has thus been created. There is further cable routing to two protective cabinets where cable shields are connected and the active cores are protected by Blitzductor® KT (predecessor of Blitzductor® CT) surge arresters. These protective cabinets (Figures 6.2 f) are the central interface between the protected volume of the engine hall and the outer area.
There turned out to be a special problem in that the underground gas tanks and gas pipelines had to be cathodically protected. Here two different levels of equipotential bonding had to be created: equipotential bonding on the level of the mentioned direct earthing • the by the foundation earth electrodes equipotential bonding on the level of the cathodical protection • the potential.
Figure 6.2 d Electrical bonding of the reinforcement of the prefabricated concrete parts
Figure 6.2 e Bonding of the reinforcement steel by means of steel strips
326
Overvoltage protection of low voltage systems
Figure 6.2 f
Protective cabinets: control room (Source: P. Biebl); total view of the protective cabinets; cable input into the protective cabinet with arresters (Source: P. Biebl)
Figure 6.2 g shows the line treatment inside and around the gas distribution station. Those cable shields leading to equipment on the cathodic protection potential are connected to a cathodic corrosion protection equipotential bus bar (CCP–EBB). The gas tank bodies and the pipes coming from the tanks are directly connected to this equipotential bonding bar. The bushing of the cable shields and the gas pipes must be insulated from the earthed reinforcement of the gas distribution station. As the gas pipe in the distribution station is at earth potential, an insulating flange had to be inserted at the entrance and the output of the station. Equipment at earth potential and the corresponding cable shields have been bonded with the equipotential bonding bar (EBB) which is directly earthed. For the purpose of lightning protection equipotential bonding the equipotential bus bar lying at cathodic protection potential (CCPEBB) and the equipotential bus bar lying at earth potential (EBB) are interconnected by suitable explosion-protected disconnection spark gaps (Figure 6.2 h). A corresponding solution has been implemented at the entrance of the cables and gas pipes into the engine hall area.
Sources HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen-Konzept’ (Pflaum Verlag, München VDE Verlag, Berlin/Offenbach, 1994 LANG, U., and WIESINGER, J.: ‘Eine Methode des Blitzschutzes für nachrichtentechnische Anlagen – Das Denken in Blitz-Schutzzonen’, de der elektromeister + deutsches elektrohandwerk, 1990, (11), pp. 39–45
Application in practice: Some examples
Figure 6.2 g
Equipotential bonding in the gas distribution station
Figure 6.2 h
An explosion protected disconnection spark gap connects the equipotential bonding bar at cathodic protection potential with the equipotential bonding bar at earth potential
327
328
Overvoltage protection of low voltage systems
6.3 Mobile radio systems Mobile radio systems are often installed on existing buildings (in a radio technically favourable site). For these systems class III (according to DIN V ENV 61024–1) lightning protection is mostly provided. This must be independent of the host building’s systems so that they will not be additionally endangered. Determination of class III protection means a radius R = 45 m (of the rolling sphere) for the rolling sphere method to specify the position and height of the air terminations. A sphere with radius R = 45 m will be rolled over that part of the building where the components of the mobile radio system are located (Figure 6.3 a). Thus, there are lightning protection zones with different levels of potential lightning danger: LPZ 0 . Direct strike is possible, undamped electromagnetic lightning • fields (e.g., antenna masts). LPZ 0 . Direct strike impossible, undamped electromagnetic lightning • fields (e.g., parts of the roof surface). LPZ 1: Direct strike impossible, damped electromagnetic lightning • fields (e.g., interior of the base station). A
B
If an electrical line crosses a zone interface, it must be protected at the crossing point. For coaxial cables this is realized by connecting the shields to earthing couplings and by their equipotential bonding. Active power and telecommunication wires will be protected by lightning current arresters at the lightning protection zone boundary 0A/1 and by surge arresters at the zone boundaries 0B/1 and higher. According to class III lightning protection there is a total lightning current loading of 50 kA (10/350 μs) for the power and telecommunication cables. To avoid uncontrolled arcing due to a lightning strike, all mobile
Figure 6.3 a
Determination of the protected zone by means of the rolling sphere method (LPZ: lightning protection zone)
Application in practice: Some examples
329
radio systems on the roof such as metal installations of electrical systems and the lightning protection and earthing system (if there is any), must be interconnected by a meshed functional equipotential bonding (MFEB). This MFEB shall include the metal components of the base station, the antenna masts, cable racks and the lightning protection system of the host building (which might already exist). For the MFEB in the area of the components of a mobile radio system, a mesh width of about 5 × 5 m shall be kept, thus obtaining a network of low impedance. The line cross sections of the MFEB can be taken from Table 6.3 a. An example of realizing the meshed functional equipotential bonding for a host building without a lightning protection system is shown in Figure 6.3 b (a). Figure 6.3 b (b), for example, shows the integration of the meshed equipotential bonding for host buildings with an existing lightning protection system. The antenna mast must be connected as directly as possible with the MFEB. When using sector or radio relay antennas they must be placed in the protective area of the mast (Figures 6.3 c). At the mast foot the incoming coaxial cables must be screwed to a ground coupling, thus obtaining an electrically conductive connection (lightning current proof) between the phase of the coaxial cable and the antenna mast. The antenna cables are to be run in steel cable conduits (cable racks, cable gutters). This prevents the cables from direct lightning strikes and the lightning field influence on the aerial cable will be damped in the case of close-up strikes. It is necessary to ensure that there is a continuous bonding of the cable gutters. This is realized by screwing the cable racks or by bonding them by lightning current proof bridging ropes (Figures 6.3 d (b) ). In addition, ground couplings are used to integrate the aerial cable at the base station into the MFEB. The meshed functional equipotential bonding of buildings with existing lightning protection system will be earthed by connection to the air terminations (Figure 6.3 b (b) ). The meshed functional equipotential bonding of buildings without lightning protection will be earthed by an antenna earthing according to EN 50 083–1:1993–09. As the bonding conductor (earth conductor) between the MFEB on the roof and the antenna earthing, the following can be used:
Table 6.3 a
Minimum cross section of MFEB line
330
Overvoltage protection of low voltage systems
Figure 6.3 b
(a)
Figure 6.3 b
(b)
Figure 6.3 b
Meshed functional equipotential bonding for a mobile radio system on the roof of the host building: (a) without lightning protection system; (b) with lightning protection system
solid wire, 16 mm • single single wire, 25 mm • 50 mmsolid steel. •
2 2
copper insulated aluminium
2
•
As the earth conductor, the following can be also used: metal installations such as continuous metal water pipes, continuous metal heating pipes on condition that: (i) there is permission in accordance with the local regulations, (ii) there is permanent continuity of the different parts, and (iii) the cross sections are at least equal to those of the above mentioned materials.
Application in practice: Some examples
Figure 6.3 c
(a) Principle: protected zone
Figure 6.3 c
(b) Arrangement in practice
Figure 6.3 c
Sector antenna in the protected zone of the antenna mast
331
frame of the building • metal continuous reinforcement steel of the concrete building • façades, railings, and subconstructions of metal façades on condition • that: (i) their cross sections are at least equal to those of the above mentioned materials and their thickness is at least 0.5 mm and (ii) there is safe vertical continuity.
332
Overvoltage protection of low voltage systems
Antenna earthing is to be carried out using one of the following means: (i) foundation earth electrode, (ii) earth electrode rod 2.5 m long, or (iii) two horizontal earth electrodes at least 5 m long, laid at least 0.5 m deep and a distance of 1 m from the foundations. The minimum cross section of every earth electrode is 50 mm2 Cu or 80 mm2 steel. Usually the base station, subdistribution and cable junction form lightning protection zone 1 (Figure 6.3 d (a) ). The electrical supplying conductors (power line, telecommunication
Figure 6.3 d
(a) Basic circuit diagram
Figure 6.3 d
Figure 6.3 d
(b) Practical arrangement
Protection of base station, subdistribution (SD) and cable junction (CJ)
Application in practice: Some examples
Figure 6.3 d
333
(b) Practical arrangement
line) entering this lightning protection zone 1 must be included in the meshed functional equipotential bonding by lightning current arresters at the zone crossing (Figure 6.3 d (a) ). Application of lightning current and surge arresters is adjusted to the low-voltage system (TT, TN–C or TN–S system) taking into account the sufficient energy coordination of both arrester types. Practical examples of the arresters and decoupling inductances introduced in Section 5.8.1 are shown in Figures 6.3 e. Owing to narrow spaces the complete protective circuit for the 230 V supply is often gathered in a service entrance box (Figure 6.3 f ). All telecommunication lines entering lightning protection zone 1 at the cable junction must also be included in the meshed lightning protection equipotential bonding by lightning current arresters (Figure 6.3 d (a) ). Often, a combination of a lightning current and surge arrester (e.g., Combi-Arrester Blitzductor® CT, Type BD), depending on the telecom interface is applied: ®
connection (a/b-wire): Blitzductor CT BD, 110 V • Analogue ISDN U interface: Blitzductor CT BD, 110 V • ISDN U -interface: Blitzductor CT BD / HF, 5 V • ISDN S -interface: Blitzductor CT BD / HF, 5 V • ®
ko
2m
®
®
2m
Conductors between base station, subdistribution and cable junction are usually run in metal conduits on the roof (on both sides connected with the MFEB) so that they remain in lightning protection zone 1, not needing special protective devices.
Sources ENV 61024–1 (VDE V 0185 Teil 100): ‘Protection of structures against lightning. Part 1: General principles’. Central Secretariat: rue de Stassart 35, B-1050 Brussels Aug.1996 EN 50 083 Teil 1: ‘Cabled distribution systems for television and sound signals. Part 1: Safety requirements’ (International Electrotechnical Commission, Geneva, 1993)
334
Overvoltage protection of low voltage systems
Figure 6.3 e
(a) TT system
Figure 6.3 e
(b) TN–C system
Figure 6.3 e
(c) TN–S system
Figure 6.3 e
Energy coordinated application of lightning current- and surgearresters to protect the power supply input of mobile radio systems at different network configurations
Figure 6.3 f
Power connection box for TN–S system (compare Figure 6.3 e, C)
6.4 Television transmitter TV transmitters (Figure 6.4 a) are usually located at high altitude or on mountain tops (Figure 6.4 b), so they are particularly endangered by lightning. Power for the transmitter is taken from the public mains.
Application in practice: Some examples
Figure 6.4 a
Transmitter mast
Figure 6.4 b
Television transmitter on a mountain
335
336
Overvoltage protection of low voltage systems
Often an overhead line from the valley is changed into an underground cable at high altitude or on a mountain top. The protective insulation in the power input circuit and safe electrical insulation by a disconnection transformer is often the protective measure in the transmitter. An especially remarkable event involving lightning damage occurred at a transmitter of the Austrian Broadcasting Service (ORF) in Styria. At the time (1981) surge arresters with a nominal discharge capability of 5 kA (8/20 μs) according to IEC 99.1 were used to protect the transmitter. Such arresters are only designed for surge currents due to distant lightning strikes. In this case the surge arresters were damaged due to a direct lightning strike on the TV transmitter (Figure 6.4 c), leaving one phase of the power supply conductively connected to the station earth. Owing to the fact that in a totally insulated power input the neutral conductor is not connected to the station earth, a short-circuit current to release the back-up fuses could not be generated. A current of about 30 A had, in fact, been flowing through the station earth resistance of about 7 Ω for several months without being noticed. During that time all accessible parts of the transmitter station which were connected to the station earth (transmitter cabin, mast and associated equipment) carried mains voltage. Apart from the danger to personnel from the hazardous contact voltages at all conductive parts of the transmitter, there was also a considerable increase in the current consumption of the installation. This undesirable condition was only identified when the current consumption of the plant was subsequently analysed.
Figure 6.4 c
Surge arresters (having a rated discharge capacity of 5 kA, 8/20 μs) of the ORF TV transmitter ‘Braunhuberkogel’ in Styria damaged by lightning strike
Application in practice: Some examples
337
This example clearly demonstrates that, in the quest to attain total ‘protective insulation’, only arresters which are extremely robust (able to carry lightning currents non-destructively) and absolutely reliable in terms of their insulation should be used. After having turned the transmitter cabin into a lightning protection zone 1 new protective devices, namely, quenching spark gaps and highcurrent spark gaps, were installed in this installation in autumn 1982 (Figures 6.4 d to 6.4 f). Lightning current counters were installed in the
Figure 6.4 d
Power supply of the ORF TV transmitter ‘Braunhuberkogel’. Lightning current-proof surge protection at the crossing ‘overhead line/underground cable’
Figure 6.4 e
Power input with protective insulation and lightning current-proof surge protection of the transmitter cabin of the ORF TV transmitter ‘Braunhuberkogel’
338
Overvoltage protection of low voltage systems
Figure 6.4 f
(a) Transmitter cabin
Figure 6.4 f (b) Detailed view of Figure 6.4 f (a)
corresponding earth connection line of the arresters at the overhead line mast and in the transmitter cabin. These had recorded 29 lightning currents at the overhead line mast and 59 lightning currents in the transmitter up to the end of 1997. These lightning strikes have been controlled without damage or interference to the transmitter.
Sources HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen-Konzept’ (Pflaum Verlag, München VDE Verlag, Berlin/Offenbach, 1994) FELDHÜTTER, W., HASSE, P., and PIVIT, E.: ‘Überspannungsschutz des Netzeinganges eines Fernsehfüllsenders auch be direken Blitzeinschlägen’. 17th International Conference on Lightning Protection (ICLP), Den Haag, 1983, Paper 3.2 EN 60099–1: ‘Surge arresters. Part 1: Non linear resistor type gapped surge arresters for AC systems’ (International Electrotechnical Commission, Geneva, 1991)
Application in practice: Some examples
339
6.5 Mobile telecommunication facility A mobile facility (Figures 6.5 a) must be protected against dangerous contact voltages and surges. In this present case surge protection of the power connection (with total insulation) was required to guarantee safe uninterrupted operation in the event of direct lightning strikes and nuclear electromagnetic pulses (NEMP). Turning the facility into a lightning protection zone 1 and a NEMP protection zone 1 was the solution to the problem. All cable entries were protected at the interface of the lightning or NEMP protection zones 0 and 1. The lightning and NEMP interferences on the power connection side
Figure 6.5 a
Transportable, metal encased telecommunication facility with line inputs protected against lightning and NEMP (1 to 5)
340
Overvoltage protection of low voltage systems
must be limited by an arrester circuit so that the protective insulation will not be endangered. A suitable arrester circuit is shown in Figure 6.5 b. A group of lightning current arresters (Figure 6.5 c) out of five spark gaps which can quench the mains follow-current (quenching spark gaps) and a high current spark gap as a disconnection spark gap is installed between the phases (L1, L2, L3, N and PE) and the shielding case of the mobile facility. The minimum AC operating voltage of this arrangement of arresters is about 5 kV and the minimum impulse operating voltage about 10 kV. The insulation between the power input circuit and the
Figure 6.5 b
Basic circuit diagram of a surge protected power connection of a mobile operating facility with protective insulation in the input circuit
Figure 6.5 c
Lightning current arrester arrangement out of five quenching spark gaps and one high current spark gap
Application in practice: Some examples
341
shielding case of the mobile facility as well as the insulation between the input and output circuit of the isolating transformer are adjusted to these operating voltages. Surges below this level, such as switching surges, are carried by the insulation. During undisturbed operation, this group of arresters ensures double insulation. The basic insulation is provided by the quenching spark gaps which have a quenching capacity according to DIN VDE 0675 Part 6; the additional insulation will be realized by the high current spark gap. Voltage peaks will arise at the arrester arrangement before and during activation, the level of which depends on the steepness of the surges. Increasing voltage steepness makes the operating voltage of the group of arresters rise according to its impulse characteristic. Owing to the enclosed spike chokes, very steep voltage peaks will be damped and thus reliably protecting the insulation of the isolation transformer (Figure 6.5 d). In the internal network of the facility in lightning and NEMP protection zone 1, on the secondary side of the isolating transformer, the TN-C-S-system is used. Any surges arising on the secondary side prior to the reaction of the arresters will be limited by varistors. For protection against very high frequency surges, especially due to NEMP effects, additional RFI bushing filters are provided. The protective conductor PE of the power cable is not necessary if protective insulation is applied. However, by using standard power cables and plugs, the protective conductor PE will be automatically carried to the coupling socket of the cable at the transportable facility. It must not terminate here in an open circuit condition because in the event of a surge a sparkover would occur in the plug and socket facility. Therefore, the protective conductor PE should be treated as if it were a live conductor and is equipped with a quenching spark gap.
Figure 6.5 d
Coordinated surge characteristics of the arrester arrangement and the isolating transformer insulation
342
Overvoltage protection of low voltage systems
In the case of a direct lightning strike into a facility on a nondefinitively earthed vehicle the worst case condition occurs when the entire lightning current enters through the power supply. Therefore, an arrester arrangement is required to meet the lightning currents according to protection class III (compare Table 4.1.1 c): resistance and minimum operating voltage must not • Insulation change considerably even after multiple lightning current loadings
•
(this guarantees a long-term protective insulation of the power input). After activation of the arresters by a surge, the ensuing mains followcurrent must be quenched automatically.
As shown in Figure 6.5 b, these requirements are distributed among several spark gaps. In terms of their insulation characteristics these quenching spark gaps correspond to the basic insulation. They will be connected at their lower end and wired via the high-current spark gap to the casing of the power connection. This spark gap, working like a disconnection spark gap, can control the entire lightning current and has excellent and very reliable insulation characteristics corresponding to the requirements of additional insulation. The series connection of quenching and high current spark gaps thus constitutes a double insulation with lightning current conductive surge protection. The spark gaps are installed in a service entrance box which can be easily inserted into the mobile facility, as shown in Figure 6.5 e.
Figure 6.5 e
Mains connection box, installed into a mobile operating facility
Application in practice: Some examples
343
Sources HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen-Konzept’ (Pflaum Verlag, München;: VDE Verlag, Berlin/Offenbach, 1994) HASSE, P., MEUSER, A., PIVIT, E., and WIESINGER, J.: ‘Überspannungsschutz eines Netzanschlusses für transportable Betriebsstätten mit Schutzisolierung bei direkten Blitzeinschlägen’, etz Elektrotechn. Z, 1982, 103, (2), pp. 52–54 E DIN VDE 0675 Teil 6: ‘Überspannungsableiter zur Verwendung in Wechselstromnetzen mit Nennspannungen zwischen 100 V und 1000 V’ (VDE Verlag, GmbH, Berlin/Offenbach) Nov. 1989
6.6 Airport control tower The planning of the new control tower of Nuremberg Airport shall be used as an example for the application of LEMP management (IEC 61312–1) introduced in chapter 4.1.3.1. In accordance with the first step of the LEMP protection management plan (cf. Table 4.1.3 a), LEMP-protection planning was executed by the planner Dr R. Frentzel (TÜV South Germany, Munich) in coordination with operator and owner of the airport who provides the new tower • the including all technical installations traffic control as a user of the new tower with its own electronic • air equipment, architect (construction planning) • the the • engineering office (electrotechnical planning). The defined target of protection was to safeguard failure-free operation of the electrical and electronic systems of the air traffic control in the case of lightning interference as far as possible. As, in this stage of planning, no data about the electromagnetic surge immunity of the different electric and electronic devices and systems of the air traffic control were available, the requirement was to achieve the utmost protection for these devices and systems against the impact of lightning and against internal interferences, by means of the structural possibilities and by the guidelines for the system installation. Correspondingly the structure was rated as a lightning protection class I project (according to IEC 61024–1). The new control tower and the corresponding operations building were then subdivided into lightning protection zones and interference protection zones, in order to define rooms of different degrees of severity with regard to conducted and field interference. Such a subdivision also makes it possible to determine local equipotential bonding points at the lightning protection zone boundaries.
344
Overvoltage protection of low voltage systems
For the planning of the air terminations by which lightning protection zones 0A and 0B are determined, an existing CAD-3D-Tower-Model (scale 1:100) was used. As Figure 6.6 a shows, a sphere (corresponding to lightning protection class I) with radius 20 m is used for the rolling sphere method. The second step, ‘LEMP-protection’ according to Table 4.1.3 a, involves determining the strike-protected areas (lightning protection zone 0B) in the outer area by means of suitable sectional drawings of the structure. Owing to the defined target of protection and the structural conditions, two lightning protection zones of graded interference levels were determined in the inner area of the control tower and the operation building. All rooms which contain electronic systems and the cables that are important for the operation of the air traffic control were classified as lightning protection zone 2, where conducted and field interference are strongly reduced. All other rooms were classified as lightning protection zone 1 for which an effective electromagnetic shield is not realizable. In lightning protection zone 1, therefore a high residual lightning field and the resulting electromagnetic coupling on lines and devices must be taken into account. The malfunction and failure of equipment in lightning protection zone 1, for example of office PCs, are accepted. By a consequent realization of the planned zone division, however, interference from devices and systems in lightning protection zone 1 on those in lightning protection zone 2 will be avoided. The power technical system rooms in the basement were classified as being in interference protection zone 1, which is comparable to lightning protection zone 1 with regard to the prevalent interference level. All
Figure 6.6 a
Tower model (1:100) and to scale rolling sphere (r=20 m) (Source: Frentzel, R., TÜV South Germany)
Application in practice: Some examples
345
rooms of lightning protection zone 2 also belong to interference protection zone 2. The interference in interference zone 1 is due to power technical switching operations and feedback from the mains. In defining lightning protection zone 1 it was considered that the metal housings of the devices, such as switching cabinets out of sheet steel, already attenuate the high frequency field interference. The interior of the metal housings is therefore considered as being in interference protection zone 0. Figure 6.6 b shows the division into protection zones. Functions of lightning protection and EMC (such as air terminations, down conductors, foundation earth electrodes, lightning protection and surface equipotential bonding, shielding of buildings and rooms against electromagnetic fields, and earthing of information technology systems) have been attributed to the metal parts of the control tower and the operation building, as there are reinforcement mats, steel pillars, metal façades, metal roof coverings, lattices, railings, stilted floors, elevator constructions etc. The basis for these functions is an electrically conductive and possibly low-impedance connection of all metal parts. For the tower this is realized by an additional netting which is put into the reinforced floors, ceilings and walls (Figure 6.6 c). The welded netting consists of flat steel strips 30 mm × 3.5 mm with a grid size of about 5 m × 5 m and is welded to the reinforcement every 2 m. For the purpose of equipotential bonding with other metal parts, fixed earthing terminals or connection lugs are made to project from the concrete at the necessary points. Lightning protection zone 2 contains the systems of the air traffic control with the highest protection requirements. The electromagnetic shield of lightning protection zone 2 essentially consists of a multilayer reinforcement of usual mesh size 10–15 cm. For the basement, for example, it was quite easy to plan an effective shield because the floor, the walls and the ceiling are reinforced all over. Thus, sufficient shielding in lightning protection zone 2 against rooms with lightning protection or interference protection zone 1 as well as against lightning protection
Figure 6.6 b
Subdivision of the basement into protected zones (Source: Frentzel, R., TÜV South Germany)
346
Overvoltage protection of low voltage systems
Figure 6.6 c Schematic representation of the additional meshed network (Source: Frentzel, R., TÜV South Germany)
Figure 6.6 d Subdivision of the air traffic controller cabin into protected zones (Source: Frentzel, R., TÜV South Germany)
zone 0 (outer area) is achieved. The window openings in the basement are shielded by the conductive bonding of the gratings which cover the (reinforced) light shafts. If non-metallic doors are planned inside the shield of lightning protection zone 2, a shielding will be realized by inserting metal sheets into the doors. These metal sheets will also be bonded with the reinforcement via the metal door frames. Not quite as easy, however, was the planning of the shield of lightning protection zone 2 in the air traffic controller cabin (Figure 6.6 d) where, due to the panoramic glass, intensive electromagnetic fields, due to lightning, must be taken into account. Shielding lattices in front of the windows or shielded panes were not accepted by the air-traffic control, as these measures would lower the visibility. Therefore, the inner air-traffic controller cabin has been divided into lightning protection zone 1 and lightning protection zone 2. Lightning protection zone 2 comprises the space under the false floor where the entire cabling is laid. This volume is shielded by a conductive false floor and lateral sheeting. The base plate under the control bench is reinforced concrete. All shielding elements are low-impedance interconnected. This lightning protection zone 2 is extended to the control desks of the air traffic controllers. The necessary shielding effect will be reached by the use of desk casings the insides of which are covered by metal foil. These metallized plates will be contacted with the metal base frame of the desks which again will be low-impedance integrated into the conductive false floor.
Application in practice: Some examples
347
The down conductors in the control tower shaft have been planned as additional netting, as already described. In the area of the operation building which contains an office section, the partly reinforced walls with additional netting, the metal façades, and in the case of steel–glass constructions, the steel pillars are used as down conductors. By using the natural elements it is not necessary to install the usual externally mounted down conductors. For the tower a common earthing system has been planned to realize a high-voltage protective earth, low-voltage operational earth, functional earth and lightning protection earth. The earthing system will be realized by using a mesh-type earth electrode within the foundation plate, thus fulfilling the requirements of DIN 18 014. Also here the netting described is used to which the flat steel strips of the additional netting in the walls as well as the down conductors are bonded. The foundation reinforcement of the 1 m thick base plate is also included into the earthing measure by welding in order to reduce the earthing resistance and to achieve close-meshed shielding. Within the scope of the lightning protection equipotential bonding all metal installations, the electrical systems, the down conductors and the earthing system are interconnected in the basement. This bonding in the basement represents, at the same time, the equipotential bonding at the boundary from lightning protection zone 0 (0A or 0B) to lightning protection zone 1 or lightning protection zone 2. The following construction principles are also applicable for installations which will enter lightning protection zone 1 or lightning protection zone 2 in the other floors from the external area. All metal installations which enter the building will be included into the lightning protection equipotential bonding directly at their point of entrance. For this purpose reinforcement terminal points have been provided at the corresponding points on the inside of the outer walls. Piping will be bonded directly or via isolating spark gaps. In the case of electrical cables from the external area it is the lightning current conductive shield itself or the wires of the cables which will be connected via lightning current or surge arresters. The shield connection and the earthing of the arresters must be carried out with low-impedance. The selection of the protective devices must, on the one hand, take into account the probable threat, while, on the other hand, the requirements of the respective zone boundary and the immunity of the equipment to be protected. Generally, lightning current arresters should be installed at the crossing from lightning protection zone 0A into lightning protection zone 1 and surge arresters between lightning protection zone 1 and lightning protection zone 2. Sometimes there is a direct change over from lightning protection zone 0A to lightning protection zone 2. In such cases the corresponding combi-arresters (chapter 5.8) must be installed. From the producer of the arresters it is required that
348
Overvoltage protection of low voltage systems
the lightning current and surge arresters be coordinated and harmonized with regard to their sparkover characteristic and discharge capability. It is also in the basement where the lightning protection equipotential bonding of the larger installations inside the building must be carried out, as there are cable tray systems, heating pipes, ventilation or airconditioning lines, fire extinguishing conduits and guide rails of elevators. Corresponding terminals are also provided for these installations. Equipotential bonding must also be carried out at the boundaries of lightning protection zones 1 and 2 for all electrically conductive parts which cross the boundaries as well as for metal parts inside the lightning protection zone. With the above-described measures a low-impedance equipotential bonding network is obtained from which it is possible to realize a surface-covering earthing of the electronic systems at the common earthing system. The use of concrete reinforcement together with additional netting as down conductor/equipotential bonding means that proximities for these structural parts of the tower can be neglected. For other structural parts the safety distance must be calculated according to the proximity formula indicated in IEC 61024–1. With regard to the calculations for the area of the air-traffic controller cabin it should be considered that the next equipotential bonding level for the electric lines is the floor of the air-traffic controller cabin, see Figure 6.6 d. Apart from lightning discharge as an external source of interference there are switching operations within the power plants which are a dangerous internal source of interference for electronic systems. Such switching operations generate high-frequency field and line-conducted interference which can influence the electronic systems in different modes of coupling. As a measure to control such interference the alreadydescribed interference protection zones have been defined. The shields at the boundaries of the interference protection zones (i.e., the metal equipment casings at the boundary of the interference protection zones 0/1 and the structural shielding measures at the boundary of the interference protection zones 1/2) have a sufficient damping effect on the fields which are radiated by the equipment itself, under the condition that the equipment casings are included with low-impedance into the equipotential bonding. Conducted interference due to switching operations is effectively limited by using shielded cables in interference protection zone 2 and by the protection measures at interference protection zone boundary 1/2. To avoid undesired influence on electronic systems by power cables, defined distances between cables of different voltage levels are maintained. For example, consider a three-layer rack pile; the following configuration might be provided:
Application in practice: Some examples
1 (bottom): signal cables < 30 V • Level Level (middle): control, measuring, • < 60 V, 2control cables < 1 kV Level 3 (top): low-voltage cables < 1 kV. •
349
telecommunication cables
Protection management against electromagnetic lightning pulses means new requirements for the construction. Additional functions such as the carrying of lightning current, earthing and shielding of the building, and equipotential bonding are attributed to the metal structures of the building. Thus, an economic realization of an effective protection system is possible. The main difficulty is that after the construction phase most of the metal structures are no longer accessible. It is, therefore, absolutely necessary to guarantee that those parts which will be covered by concrete or soil meet the regulations and so stringent control is necessary during the construction phase.
Sources IEC 61312–1: ‘Protection against lightning electromagnetic impulse. Part 1: General principles’. Centrel de la Commission Electrotechnique Internationale. 3, rue de Varembe, Genève Jan. 1995 ENV 61024–1: ‘Protection of structures against lightning. Part 1: General principles’. European Committee for Electrotechnical Standardization, Central Secretariat, rue de Stassart 35, B-1050 Brussels Jan. 1995 DIN 18 014: ‘Fundamenterder’ (Beuth Verlag, Berlin) Feb.1994 FRENTZEL, R.: ‘Massnahmen des Blitzschutzes und der EMV für den neuen Tower am Flughafen Nürnberg’: DEHN u. SÖHNE Druckschrift Nr. 657 6. Forum für Versicherer: Blitz und Überspannungsschutz – Massnahmen der EMV, April 1998 pp. 79–85
Chapter 7
Prospects
The requirement for electronic information technology systems not to be disturbed or even damaged by direct or close-up lightning strikes has led to new quality requirements and a new dimension in the area of lightning protection engineering. Lightning protection has been integrated into the world of electromagnetic compatibility (EMC). The so-created concept of lightning protection zones has turned out to be a very efficient management method and is proven as a universal organizing principle in numerous complex problems. Meanwhile, the concept of lightning protection zones has been specified as generally the method most appropriate for the protection of any kind of structure with electronic equipment. To this end the Technical Committee (TC) 81 of the International Electrotechnical Commission (IEC) has elaborated upon the standard which shows the principles for protection against ‘electromagnetic lightning pulses’. This has been published as IEC 61312–1. This book has introduced practice-proven components and protective devices by which it is possible to plan and realize complete lightning/ surge protection concepts for many kinds of complex systems and structures. The protective measures exemplified and devices available are applicable, not only in new projects but also in existing systems which can be retrofitted so that a sufficient protection can still be attained. Subsequent installation, however, will be at higher cost and with a lower efficiency. The standards committees are currently working on standards which treat the following subjects: analysis as to the failure of electronic systems due to lightning • risk electromagnetic shielding effects of existing metal structure com• ponents against lightning fields coordinated application of lightning current and surge arresters at the • interfaces of the lightning protection zones
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of the concept of lightning protection zones to existing • application structural systems with electronic equipment. Along with the practical protection requirements, producers are accompanying these activities with improvements to protection devices. As a guiding example of such an improvement the lightning current arrester DEHNport® Maxi now safely extinguishes mains followcurrents of up to 50 kA.
Sources HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen-Konzept’ (Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach, 1994) IEC 61312–1: ‘Protection against lightning electromagnetic impulse – Part 1: General principles’ (International Electrotechnical Commission, Geneva) Feb. 1995
Index
abattoir 22 aerials 27–29, 31, 329 air termination 127–129 rods 128 roof superstructures 128, 129 wires 128 air termination systems 69, 78, 79, 84, 85, 87 air traffic control 343–346 aircraft, damage 36–38 airport control tower, protection 343–349 airports, damage 37 alarm systems 68, 313–317 protection 313–317 analogue a/b-wire terminal 286–292 angle of protection 78 animal breeding farm 17, 21 automatic feeding 17, 21 ventilators 17, 21 antenna mast 328, 329, 331, 332 Apollo 12 space ship 38 application-neutral cabling 255–261 arrester backup fuses 196–204 arrester classes 109, 115, 117, 120–122, 154–156, 160 arrester disconnecting devices 117–120 arrester tests 115–119, 227 disconnecting devices 117–119 operating duty 117, 118 test currents 115–117 thermal stability 117 arresters 24, 26, 79, 98–101, 113–126, 153–292 breaking capacity 120 combined 214, 228, 253, 254 coordination 120, 121, 125, 218, 220 cut-off frequency 217, 218, 226 decoupling 180–183 discharge capability 120, 124, 223 limiting voltage 215–217
N-PE 121, 122 nominal current 124, 217, 218, 226 nominal voltage 124, 214, 216, 226, 227 operating frequency range 124 protection level 119, 124, 215, 227 rated voltage 119, 124 standards 113–126 test values 99, 116 valve-type 167, 168 arresters, application in different system configurations 182–197 IT-system 184, 185, 196, 197 TN-system 184, 185, 188–192, 333, 334 TT-system 184, 185, 193–195, 333, 334 arresters for cathodic protection systems 246–249 arresters for equipment inputs 175, 176, 208 arresters for information technology 122–125, 206–292 arresters for lightning protection equipotential bonding 157–167 arresters for measuring and control systems 209–252 arresters for overhead lines 155–159 arresters for permanent building installations 167–174, 208 arresters for power engineering 113–122, 155–205 arresters for socket outlets 174–176, 208 arresters, graded application 178–183, 206 arresters in Euro-card format 248, 250, 251 arresters in LSA-Plus technology 248, 251, 252 arresters, selection 119, 120, 124, 125, 223–228
354
Index
atmospheric overvoltages 45–61 magnitude 60, 61 backup fuses for arresters 196–204 Blitzductor® 208–249 construction and mode of functioning 210–222 examples of application 228–240 selection criteria 223–228 building installations, protection 167–174, 208 building regulations 69, 70 building services control system 22, 23 buildings 39, 40, 69, 76, 77, 81–85, 88–92, 295–304 metal components 83, 84, 90, 92 protection 295–304 room shielding 84, 88–92 burglar alarm systems 313–315, 317 bus systems 309–313 cable coupling resistance 57 cable television 32 cables 56, 57, 61, 95–97, 138–143 ducts 95–97, 140, 141 shielding 138–143 supporting structures 142 cabling systems 255–257 generic 255, 256 primary 255, 256 secondary 255, 256 tertiary 255, 256 catastrophic damage 39–41 cathodic protection systems 246–249, 326, 327 central computer, protection 307–309 central heating, protection 302, 304–307 cereal processing 243 chemical industry 196, 243 chemical plant 11–13 close-up strike 45, 242 cloud-to-cloud lightning 45 coal processing 243 common mode protection 254 computer integrated business 1 computer integrated manufacturing 1 computers, damage 5, 6, 16–20, 32, 34, 35 computers, protection 55, 207, 209, 254, 307–309 connection components, standards 113 consequential damage 77 contact voltage 184 coordination between arresters and equipment to protect 178–183, 220
coordination characteristics 220–222, 227 corrosion protection 246–249 coupling of surge currents on signal lines 57–60 capacitive 59, 60 inductive 58, 59 ohmic 58 coupling path 43, 44 damage statistics 5–10, 70 data networks, protection 255–292 data telecontrol transmission 277–292 by analogue a/b-wire terminal 286–292 by ISDN base terminal 277–284 by ISDN primary multiplex terminal 284–286 DC line technique 314, 315 decoupling elements 206 decoupling of arresters 180–183 decoupling choke 180–183 decoupling length 180, 181, 183 differential mode protection 254 direct strike 45, 60, 242, 328, 336 disconnection 61, 62 disconnection spark gap 326, 327, 340, 342 disconnectors 167, 168, 170, 171 remote indication 170, 171 dissolution pressure 246 distribution cabinet 30 distributors 255–257, 262–264 down conductor systems 78, 79, 84, 85 drop-cable 267 earth bus 92, 131, 135, 146 earth electrode 90, 332 earth-fault current 193 earth ring bus 146–149 earthing systems 78, 79, 84, 85, 90, 111, 295, 296, 298, 299, 347 electrical systems of buildings 103–110 protection 103–110 surge protection standards 103–110 electrochemical corrosion 246, 247 electromagnetic cage 129, 130 electromagnetic compatibility (EMC) 2, 3, 43, 63, 68, 112, 114, 115, 351 standards 112, 114, 115 electromagnetic interference 67, 68 electromagnetic lightning fields 328 damped 328 undamped 328 electronic data processing systems 1, 9
Index electronic equipment protection 80 electrostatic discharge 7, 17, 20, 43 engine hall 323–325 equipment inputs, protection 175, 176, 208, 253, 254 equipotential bonding 13, 16, 48, 69, 78–81, 90–95, 97, 99, 111, 145–149, 190–192, 194, 195, 197, 207, 244, 302, 303, 310, 322, 325–329, 345, 347, 348 meshed functional equipotential bonding 329, 330 equipotential bonding bar 90–93, 147–149, 253, 296, 297, 326, 327 equipotential bonding lines 141, 147 equivalent earth resistance 47, 48 equivalent surface 76 Ethernet 10 Base T 265, 266 Ethernet coax-cabling 267–272 thickwire 267, 269, 271 thinwire 267–269, 272 Ethernet twisted pair cabling 265–269 European Installation Bus (EIB) 309–313 Ex-zones 241, 243–245 explosion-protected spark gap 150–152, 326, 327 explosions 10–13, 24, 27, 241, 243 nuclear 44, 68 explosive atmosphere 238, 241–243 external lightning protection 16, 69, 78, 79 factories, protection 295–323 factory hall, lightning protection 295–299 Faraday cage 13, 16 Faraday hole 13, 16 Fast Ethernet 100 Base TX 265, 266 fault voltage-operated protective device 185, 193, 196 Fax machine 281 field-bus systems, lightning/surge protection 231–236 financial loss 1, 8, 13, 16, 17, 22, 308 fire alarm systems 313–316 flashover 10, 16, 22 follow-current 199–204, 342, 352 fuses 196–204 gas discharge arresters 215–217, 224, 225 gliding spark gap 161, 163, 165, 166, 199, 200
355
hazardous areas, damage 10–15 high current spark gap 151–153, 337, 340–342 hospitals 39 houses, damage 27–36 hybrid generator 293, 294 impulse earth resistance 45, 48, 49 voltage drop 48, 49 impulse line technique 314 incoupling 22, 58 induced voltages in metal loops 49–56, 58 square-wave 49–54 transverse 50–52, 58 industrial plants, damage 15–24 industrial plants, protection 295–323 information technology equipment protection 73, 122–125, 206–292 insulation coordination 105, 106, 178 insulation monitoring device 185, 196 insulation resistance 244, 245, 342 insurance 9, 10 interference model 43 interference protection zones 344, 345, 348 interference sources 43, 44 internal lightning protection 16, 69, 78, 79 intrinsic safety 241–244 intrinsically safe measuring and control circuits 238–246 ISDN base terminal 277–284 ISDN primary multiplex terminal 284–286 kerosene tank 10–12 lightning current 2, 17, 27, 28, 32, 45–49, 55, 56, 67 components 46 parameters 46, 78, 160 partial 46, 47 rate of rise 49, 50 lightning current arresters 153–155, 157–167, 177–183, 188–203, 206, 207, 211, 222, 228, 234, 262, 263, 275, 280, 285, 287, 288, 307, 314, 319, 320, 323, 328, 340, 341, 352 lightning current counter 293, 294, 337, 338 lightning damage 7, 8, 10–41 direct 7, 8, 34 examples 10–41 indirect 7, 8, 34, 35
356
Index
lightning discharge 2, 3, 68 lightning electromagnetic impulse 43 lightning electromagnetic impulse protection (LEMP) 80, 82–102, 343, 344, 351 costs 101, 102 inspection 100, 101 installation 99, 100 planning 83–97 realization 97–99 supervision 99, 100 lightning interference standards 64 lightning protection levels 74, 75, 77, 78, 83, 155, 158, 194, 295 lightning protection systems 16, 67–102, 223–225, 351 building integrated 84–86 cable routing and shielding 94–98 efficiency 77 equipotential bonding networks 90–94 external 16, 69, 78, 79 flow diagram 75, 76 internal 16, 69, 78, 79 isolated 84–86, 128 partly isolated 84–86, 128 planning 83–97 protection levels 74, 75, 77, 78, 83 room shielding 84, 88–91 standards 69–103 zones 79–85, 92–99, 102 lightning protection zones 79–85, 92–99, 102, 177–179, 255, 295, 303, 304, 307–309, 323, 325, 328, 343–348, 351, 352 lightning strikes 45–57, 60, 242, 328, 336 close-up 45, 242 direct 45, 60, 242, 328, 336 remote 45, 56, 57, 60, 242 longitudinal current 254 low-voltage overhead lines 155–159 LSA-Plus technology 248, 251, 252 measuring and control systems, protection 209–252 meshed functional equipotential bonding (MFEB) 329, 330, 333 line cross section 329 mesh width 329 military applications 152 military installations 68 mobile radio systems, protection 328–334 mobile telecommunication facility, protection 339–343 modem 286, 288, 290
N-PE arresters 121, 122, 166, 167, 193, 194 NET-Protector 257–259, 266 network card 269, 272 network terminal 279, 284 NH fuses 200–204 explosion 201, 202 melting 200, 201 no melting 200 nuclear electromagnetic pulse (NEMP) 44, 339, 341 nuclear power station 68 oil refinery 10, 13, 14 optical fibre transmission system 144, 145, 256 optocoupler 145, 146 optoelectronic connection 143–146 osmotic pressure 246 overcurrent protective device 185, 187–189, 193, 196, 203 overhead lines, protection 155–159 overvoltage category 105–108 peak-load power station 323–327 petrol tanks 10, 11, 13, 15 temperature control 10, 11 pipeline 247, 249 pipeline valve station 246 potentially susceptible equipment 43, 44 power engineering systems, protection 113–122, 155–205 power stations, protection 323–327 power supply systems, damage 24–27 printing press 22–24 protection against direct contact 182, 184 protection in case of indirect contact 182, 184–188, 193, 196, 202 protection levels 74, 75, 77, 78, 83, 155, 158, 194, 295 angle of protection 78 efficiency 77, 78 lightning current parameters 78 mesh size 78 rolling sphere radius 78 protective bypass 254 protective circuit 206 protective devices for analogue a/b-wire terminal 286–292 protective devices for application-neutral cabling 255–261 protective devices for data networks/ systems 255–292
Index protective devices for Ethernet coaxcabling 267–272 protective devices for Ethernet twisted pair cabling 265–269 protective devices for ISDN base terminal 277–284 protective devices for ISDN primary multiplex terminal 284–286 protective devices for power supply inputs and information technology inputs combined 253, 254 protective devices for standard cabling 271–278 protective devices for token ring cabling 262–265 protective insulation 340, 341 quench gap 166, 167 quenching spark gap 337, 340–342 RADAX-flow technology 161, 164, 203, 204 radio paging system, protection 318–321 radio systems 29, 31, 32, 39, 254, 318–321, 328–334 rated surge voltage 105, 107, 108 reactive current compensation system 22 reinforcement 129–134 remote strike 45, 56, 57, 60, 242 residual current circuit breaker 17, 22 false tripping 17 residual current device 17, 22, 185–189, 193, 194, 196, 202 resistance thermometer 236 risk analysis 74–78, 80, 351 risk of failure 67 rockets 36, 38 rolling sphere method 84, 87, 128, 328, 344 drawing 87 scale models 87, 344 safety clearances 78 shielding 84, 88–92, 129–143, 351 buildings 129–138 cables 138–143 electronic cabinets 137 lines 138–141 metal façades 131, 136 rooms 84, 88–92, 130, 131 steel reinforcements 129–134 short-circuit current 193 socket outlets, protection 174–176, 208 spark gaps 150–153, 155, 157–159,
357
161–166, 198, 199, 200, 203, 204, 326, 327, 337, 340–342 explosion-protected 150–152, 326, 327 gliding 161, 163, 165, 166, 199, 200 high-current 151–153, 337, 340–342 isolating 150–153 quenching 337, 340–342 RADAX-flow technology 161, 164, 203, 204 sparkover voltage 150, 151 standard cabling 271–278 standards 67–126 arresters for information technology 122–125 arresters for power engineering 113–122 connection components 112, 113 electromagnetic compatibility 112, 114, 115 European 67 international 67 lightning protection 69–103 protective devices 113–126 surge protection of electrical systems of buildings 103–110 surge protection of telecommunications systems 110–112 state of limited overvoltage 105, 106 in-system 106 protective 106 store and dispatch building, lightning protection 296–304 strain gauges 229, 230 surge arresters 153–159, 167–197, 206–208, 211, 228, 234, 242, 253, 254, 257, 259–261, 263–272, 274–290, 307–314, 319–323, 328, 336 surge current 45, 46, 56–60, 63 cables 56, 57 coupling 57–60 surge current counter 293, 294 surge damage 5–10 surge immunity 207, 218, 219 surge limiter 123 surge protection 67, 68, 103–112, 224, 225 electrical systems of buildings 103–110 longitudinal 224, 225 standards 103–112 telecommunications systems 110–112 transverse 224, 225
358
Index
surge protective devices 153, 154, 178, 206, 257, 260, 261, 266: see also arresters surge voltage 45, 46, 63 surge withstand voltage 105, 107 switchbays 24, 26 switching electromagnetic impulse 43 switching overvoltage 6, 7, 22, 61–64 disconnection of a capacitance 61, 62 disconnection of a transformer 62 earth fault in the floating network 62 telecommunication systems, protection 53, 54, 110–112, 146–149, 223, 224, 279, 339–343 equipotential bonding 146–149 mobile 339–343 surge protection standards 110–112 telephone systems 17, 28, 31, 32, 34, 35, 39–41, 210 telephones 281, 288 television sets 32, 254 television transmitter, protection 334–339 temperature measuring equipment, surge protection 236–240 textile industry 16 token ring cabling 262–265
traffic lights 28, 32, 34 transceivers 267–269 transformer substation 24, 25, 27 transmitter mast 335, 336, 338 transverse voltage 50–52, 58, 253 Twinax cabling 273, 274, 276–278 valve-type arresters 167–170 disconnectors 167, 168, 170 protection characteristic 169 voltage and current characteristics 167, 169 varistors 170–174 U/I characteristic 172, 173 zinc oxide 170–172 vehicle weighbridge, lightning/surge protection 229–233, 320, 322, 323 video control system, protection 316–321 vital infrastructure 40, 41 warehouse protection 296–304 weighbridge 229–233, 320, 322, 323 wind power stations, damage 38–40 rotor blades 38, 39 zinc oxide varistors 170–173 discharge capability 172, 173 U/I characteristic 172, 173
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