High Voltage Surge Arrester Product programme
Safe, secure and economic supply of electricity – with ABB surge arresters A new generation of overvoltage protection – backed by 65 years of experience The ABB factory in Ludvika, Sweden is a pioneer in overvoltage protection of power equipment. Our surge arresters are the Silent Sentinels protecting electrical equipment in power systems and industries all over the world since 1938. ABB was also one of the pioneers in the introduction of gapless ZnO (metal-oxide) arresters in the late seventies. The porcelain-housed arresters, type EXLIM, and silicone polymer-housed arresters, type PEXLIM are the latest generation of ABB ZnO arresters. Both types use the same blocks known for their excellent energy capability and low protection levels. PEXLIM arresters are enclosed in composite housings of silicone polymer developed after years of research. While EXLIM arresters have a given place in the substation, the PEXLIM arrester range permits greater flexibility in substation installations and opens new areas of application, e.g. as transmission line arresters using the PEXLINK concept.
Availability Secure availability of power supply is high on the list of user demands. Users have difficulty to accept interruptions in supply that cost them loss of production or damage to sensitive equipment connected to the network. With the continued privatisation of the electrical industry, consumers can now collect steep fines or change suppliers with ease. Quality, both in design and manufacture, is the essential ingredient in building reliable equipment. Correct application of our arresters ensures reliable supply with minimum interruptions to the consumers. Expensive “down-time” for overhaul and repairs of major equipment is also reduced or eliminated. ABB
ABB
meets the demands of quality assurance as stipulated in ISO 9001. The products and the manufacturing process also comply with ISO14000 and we continuously strive to reduce any negative environmental impact.
Safety In order to protect other power equipment from dangerous overvoltages, the arresters themselves are employed in the most exposed locations. Hence, under extreme adverse conditions, they may be overstressed. However, our arresters are designed to fail safely and thus protect the other equipment even during such an event. Both the porcelainhoused and polymer-housed designs are tested according to the stringent criteria of IEC standard 60099-4 for safe short-circuit capability.
Insurance In a typical substation, the cost of providing adequate overvoltage protection using arresters is a very small fraction of the cost of the substation. This cost can easily be accepted if it is seen as an insurance premium for overall economy. Naturally, only the best insurance cover should be considered.
Economy Proper selection and placement of arresters permits the reduction in the insulation withstand strength of the major equipment in a station. This can have a significant impact on reducing the overall cost of the station. With their exceptional protection performance, ABB arresters are therefore the logical choice to protect the heavy investment in other capital equipment. They make a very attractive investment that improves both short-term and long-term profitability.
EXLIM Porcelain housed arresters — Our experience is your assurance Experience ABB ZnO arresters have been in service since 1979, which speaks of our long experience with this technology. Our arresters are in service in all climates and conditions, including
– Cold northern countries with very low temperatures (-60 ˚C) and ice – Hot deserts, with very high temperatures (+60 ˚C) and sand pollution – Earthquake-prone areas – Coastal locations with continuous salt pollution and strong winds. Stability and security EXLIM arresters have a robust and stable construction, well matched with that of the other apparatus in the substation. In the unlikely event of an overstress beyond design parameters, EXLIM arresters fail in a safe mode. During such an event, the internal arc created by the short-circuiting of the inner components is very
quickly transferred safely outside the housing by specially designed pressure-relief devices. This avoids violent shattering of the housing and thus the risk for damage to nearby equipment or injury to personnel is extremely low.
Wide range of application The range of EXLIM arresters is very wide. Single-column arresters are available with different rated voltages in a variety of energy ratings from IEC Line Discharge Class 2 to Class 5 (highest as per IEC) for all the transmission voltages worldwide. Built-up of standard components, the designs cater to both standard and non-standard applications.
EXLIM R
EXLIM Q
EXLIM P
EXLIM T
System voltages
52 - 170 kV
52 - 420 kV
52 - 550 kV
245 - 800 kV
Rated voltages
42 - 168 kV
42 - 420 kV
42 - 444 kV
180 - 624 kV
Nominal discharge current (IEC)
10 kA
10 kA
20 kA
20 kA
Line discharge class
Class 2
Class 3
Class 4
Class 5
ABB
ABB
6
PEXLIM silicone housed arresters — Flexibility at its best Building on experience PEXLIM arresters, using the same blocks as the EXLIM arresters, match their electrical performance. The substitution of a composite polymer material for porcelain leads to additional advantages by way of minimised weight, flexibility of erection and highly improved pollution, seismic and short-circuit performance.
Unique characteristics Silicone is highly hydrophobic. This is an advantage in its performance under polluted conditions – better still, any reduction in hydrophobicity under constant heavy pollution is recouped automatically after the pollution episode has passed or reduced. This unique feature of silicone is made possible via low molecular weight (LMV) silicone oil propagating through the pollution layer to keep leakage currents low and ultimately restore surface hydrophobicity. Silicone insulators therefore require little or no cleaning in service. The PEXLIM family of silicone-housed arresters comes in two different designs: Directly moulded and High strength (HS) tube design.
Design highlights – Directly moulded ABB employs a unique patented design to enclose the ZnO blocks under axial pre-compression in a cage formed of fibreglass-reinforced loops fixed between two yokes. An aramide fibre is wound over the loops resulting in an “open cage” design.
PEXLIM R
This results in high mechanical strength and excellent short-circuit performance. During manufacture, each arrester module is passed through a computer-controlled cleaning and priming process before being loaded in a vulcanizing press wherein silicone is injected to bond directly to the active parts, leaving no inter¬nal voids or air spaces. The result is a complete seal along the entire length of the arrester and hence no gaskets or sealing rings are required.
Flexibility with strength The low weight and slim profile permits erection in locations where space is limited. The arresters can be mounted at any angle, including underhung from the station structures or even the conductor themselves.
Super safety During overstress conditions, the “open-cage” design permits the arc to escape directly through the housing at several points; eliminating the need for any pressure-relief devices. Further, since silicone is a very soft material compared to porcelain, there is no chance of any damage to other equipment even very close to the arresters. Additionally, the material is self-extinguishing and easily fulfils the IEC standard in this regard. Hence, PEXLIM arresters may be employed on transformer tanks close to the bushings or on transmission towers at any point in the line without any danger.
PEXLIM Q
PEXLIM P
System voltages
52 - 170 kV
52 - 420 kV
52 - 420 kV
Rated voltages
42 - 192 kV
42 - 360 kV
42 - 360 kV
Nominal discharge current (IEC)
10 kA
10 kA
20 kA
Line discharge class
Class 2
Class 3
Class 4
ABB
ABB
HS PEXLIM — High strength silicone housed arrester
Tube design for higher mechanical strength In special cases with very high demands for mechanical strength, the moulded design may not provide the optimal solution, particularly at system voltages above 420 kV. Instead, what is required is a mix between the features of the standard EXLIM and the moulded PEXLIM designs. The high strength PEXLIM tube design provides the solution by offering comparable mechanical strength to EXLIM arresters, but with much less mass. The seismic and pollution performance is in line with the moulded
PEXLIM arresters and thus superior to conventional porcelain designs.
Design highlights - HS tube The basic concept is the replacement of the porcelain housing used with EXLIM arresters by a fibreglass tube housing onto which the silicone sheds are vulcanised. The metal flanges are integrated onto the tube prior to the vulcanising process. The ZnO blocks, internal arrangement, pressure-relief and sealing devices are similar to those used for EXLIM arresters.
HS PEXLIM P
HS PEXLIM T
System voltages
245 - 550 kV
245 - 800 kV
Rated voltages
180 - 444 kV
180 - 264 kV
Nominal discharge current (IEC)
20 kA
20 kA
Line discharge class
Class 4
Class 5
ABB
10
ABB
PEXLINK – Secure supply all the way
The concept The low weight and flexibility in erection associated with PEXLIM arresters, combined with automatic disconnecting device and suitable linkages, opens up interesting applications and is the basis of the PEXLINK Transmission Line Arrester (TLA) concept.
Lightning protection for transmission line insulators While substations are well protected from direct lightning by earth mats and shield wires, the transmission lines themselves have often been neglected in this respect. In areas exposed to high lightning activity, this may lead to frequent interruptions in the power supply. Even with fast re-closing of lines after a fault, brief interruptions are nonetheless unwelcome to consumers with process industries or sensitive equipment. Surge arresters connected across the insulators at specific locations (e.g. high tower footing impedance) along a transmission line minimize such interruptions and often eliminate them altogether. While the idea is not new, it could not be realized earlier since porcelain-housed arresters were too
ABB
heavy for easy suspension in the towers or lines and the risk of damage from falling porcelain was too great. PEXLIM arresters are the ideal choice for this application and the PEXLINK concept permits quick and automatic disconnection of overstressed arresters; eliminating the need for immediate replacement to permit line-reenergization.
Switching surge control of long transmission lines Long EHV lines are prone to high overvoltages along the line during switching operations. Traditionally, the solutions have been higher line insulation or the use of preinsertion resistors for the switching circuit breakers. The modern solution, which is more economical and maintenance-free, is the use of arresters at the line ends and, where required, at other points along the line. Here too, PEXLIM arresters have obvious advantages in view of their low weight and flexible erection as they can be attached directly to the breakers or the lines. Further details of the above as well as other applications can be found in catalogue 1HSM9543 12-10en.
11
12
ABB
Monitoring the health of surge arresters
Watching and waiting Well-designed and tested, ABB surge arresters are maintenance-free and have a long in-service life. Since they are sealed units, they cannot be examined periodically (in contrast with other HV equipment) and live-line tests are difficult and expensive – often costing more than the arresters themselves. The general principle is therefore to limit maintenance to occasional cleaning of the housing and to estimate their condition based on service years only. Increasing interest for on-line monitoring of all equipment, however, has resulted in development of some special equipment even for arresters.
Surge counter, EXCOUNT-A The simplest monitoring equipment is a surge counter. The main purpose of this instrument is to record the number of significant surges through the arrester to which it is permanently connected. An abnormally higher count of surges in one phase as compared to the other two may indicate potential problems. However, the information may not be sufficient for making a definite decision regarding the need for replacement.
ultimately occurs, leading to an arrester overload. Early detection of this harmful increase may prevent a failure and an unplanned shutdown. Hence, a good monitor should be able to detect the arrester leakage current and isolate and measure its resistive component. This may be done continuously or at intervals coinciding with regular maintenance of the station equipment.
Monitoring system – EXCOUNT-II ABB’s advanced monitoring system, EXCOUNTII, may be installed for direct monitoring of surge arresters while in-service and on-line. This system comprises a sensor unit mounted on each arrester; a common hand-held transceiver unit for remote reading and software for downloading and analysis of the readings. The sensor unit is connected at the earth terminal of the arrester and is fully short-circuit proof. Its built-in power supply is charged by solar cells as well as the electric field surrounding the arrester. The sensor unit registers not only the number of discharges through the arrester but also notes their amplitude and time-stamps each event. In addition, the total and resistive leakage currents are able to be measured. The information is fed by radio link from a safe distance to the transceiver whenever called upon to do so. By using suitable software, complete records can be stored for analysis. EXCOUNT-II can be used with any gapless ZnO arrester, irrespective of its make.
Resistive current is the key When a ZnO block ages or otherwise deteriorates, the arrester’s resistive current and hence power losses increase permanently. This results in an increase in the temperature, which, in turn, increases the resistive leakage current and so on until the housing can no longer dissipate the heat generated, and a so-called thermal runaway
ABB
13
Special solutions for high energy applications
Optimized savings Enormous savings can be achieved in the design and cost of special equipment, e.g. thyristors in the HVDC valves, capacitors in series compensation and similar, when the arresters and varistors (multi-column high-energy ZnO blocks) are carefully designed for each special application.
Series Compensation (SC) Overvoltage protection for series capacitors consists primarily of a large bank of high-energy ZnO blocks (termed “varistors” by ABB) connected in parallel with the capacitors. For both external and internal faults, the varistors must maintain the desired protection levels across the capacitors by shunting and absorbing a large amount of energy. It is sometimes uneconomic to design the varistors for every possible fault condition. In such cases, the varistors themselves are protected by parallel-connected spark gaps. When a pre-set level of energy has been absorbed or when the set temperature of the varistors is exceeded, the varistors are bi-passed by forced triggering of specially designed outdoor-type spark gaps. Since the gaps are not self-extinguishing, the current in the arc is interrupted by parallel-connected rapid-closing contacts of a specially designed breaker. ABB manufacturers all the required components for overvoltage protection in close co-operation with the supplier of the compensation scheme. Special standards govern the design and testing of components for this application and a high degree of specialized competence is required.
14
Energy varistors, MXE Depending on the desired protection levels, temporary overvoltage conditions and the energy absorption capability, the varistors are built up of multiple columns of series-connected ZnO blocks. ABB has the technique and the experience to manufacture such varistors. The energy impulses have a high-frequency component, leading to increased stress on the blocks and the housings which must be taken into account in the design of the varistors. Varistors may be housed in porcelain or polymer. The former has the advantage of accommodating multiple columns in each housing. The latter has the advantage of flexible and easy erection combined with compactness and low weight in the form of rackassembly. This alternative has a great advantage when expensive EHV insulated platforms are to be designed for accommodating them. Varistors with a single-impulse energy up to 140 MJ have been delivered.
Static Var Compensation (SVC) SVC schemes often require arresters with energy capability exceeding that provided by a single ZnO column. However, they are much smaller than those for SC schemes. Standard surge arresters (EXLIM and PEXLIM) are easily adapted to cope with these requirements.
High Voltage Direct Current (HVDC) The electrical stresses in a HVDC scheme range from sinusoidal stresses at power frequency (standard AC equipment) to complex stresses at high frequencies (AC and DC filters) to unidirectional stresses (DC equipment). Special care has to be taken when dimensioning the blocks and the arresters to account for the different effects of these stresses. Blocks for normal AC applications are unsuitable for DC application. The energy stresses can be substantial and must be taken into special consideration during the design to ensure adequate energy capability and current sharing. Arresters for HVDC schemes are specially designed and tested in accordance with CIGRÉ recommendations, which are universally accepted.
ABB
Expanding frontiers with continuous research and development
One step ahead of the competition ABB in Ludvika welcomes the challenges of new designs and applications and has always been at the forefront in arrester technology. This is possible thanks to our teams of dedicated technical staff, good management, allocation of large resources and the presence of three internationally recognised laboratories within walking distance from each other. We also have the good fortune to be actively associated with internationally reputed utilities in their search for better material and performance.
Technical facilities Two specially designed and equipped laboratories for ZnO material testing and for performing electrical tests on ZnO blocks are at the heart of our innovative and quality products. The former is also a pilot plant where new processes and recipes can be trialled full scale before being released to production. The latter has all the special equipment for running the tests and is, in fact, better equipped in this regard than most independent laboratories. There are three large, well-equipped and independent laboratories (STRI, ABB High Voltage Laboratory and ABB High Power Laboratory) within walking distance from the manufacturing plant in Ludvika. This permits us to thoroughly and continuously test our designs and products. Where needed, we employ other large independent laboratories like KEMA (Netherlands), CESI (Italy), IREQ (Canada), etc. All these laboratories are equipped with the most modern equipment for the purpose at hand.
margins. Different dimensions permit a large variety of standard arresters as well as client-specific solutions with regards protection levels and energy capability. Continuous basic and applied research is carried out in our laboratories with a view to improvement of energy capability, impulse-current, protective levels, mechanical strength, etc. At the same time, research in process techniques, coupled with intensive monitoring and frequent tests during production, ensures both reduced throughput times and rejects.
Resources ABB re-invests a very high percentage of its turnover in R&D. Our technical staff take an active role in International Standards work and our designs are often tested to meet forthcoming standards where they are deemed more stringent. This is an added benefit to the user since he can be confident that the arrester purchased today will also likely fulfil forthcoming requirements.
ZnO blocks, the heart of all operations The most important component for the arresters (and varistors) is the ZnO block. The sizes of blocks are matched to the demands for different line discharge (energy) classes as per IEC 600994 and ABB is one of the very few manufacturers to develop and manufacture class 5 blocks. Strong focus on quality, from raw material until finished ZnO blocks, ensure that they survive the designed stresses with ease and with good
ABB
15
Photo: Hasse Eriksson, Mats Findell Publication 1HSM 9543 11-01en, 2006-03 Edition 4, High Voltage Surge Arresters
NOTE: ABB Power Technologies AB is working continuously to improve the products. We therefore reserve the right to change designs, dimensions and data without prior notice.
ABB Power Technologies High Voltage Products 771 80 LUDVIKA Tel: +46 (0)240 78 20 00 Fax: +46 (0)240 78 36 50 E-post:
[email protected] Internet: www.abb.cm/arrestersonline
