MAGAZINE FOR CUSTOMERS OF THE PFISTERER COMPANIES IN SWITZERLAND AND SOUTH AFRICA
JunE 2011
Business
Business
Business
IXOSIL ESF/EST:
Tensorex C+:
page 4
page 5
2DIREKT: Transformer TRANSFORM, MEEE, Changes at connections today INMR World Congress PFISTERER Holding
New generation
Constant tension
Quality to counter power failures
page 6
HOT SPOT Contact page 2
Power-double
Medupi – Spitskop 400 kV overhead power line project page 7
A great step forward
New PFISTERER LSO (Local Sales Office) opened in Beijing page 8
Group
page 9
Group
page 9
Technology
Corona protection for composite insulators page 10
Business Editorial
Jürgen Kraus Director PFISTERER IXOSIL AG
Dear readers,
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CoC Components: Contact technology seminar series
Contact – quality to counter power failures The figures prove it: high quality contacts are the foundation of reliable power supply. Poor design, manufacture or installation causes the most power failures. PFISTERER is informing power system engineers worldwide in a series of seminars on contact technology. In focus: exchange of experience from the energy markets and the basics of contact technology.
The earthquake in Japan, the tsunami that followed and its effects have moved all of us deeply. The suffering of the people and the destruction of the infrastructure have reached almost unimaginable proportions, even though we cannot yet begin to count the final cost. Whether the actual cause lies under the heading of «residual risk» or, as has been suggested recently, lack of adequate planning, will probably never be decided definitively. This tragic event has made it clear to all of us how important and essential a reliable and safe infrastructure is, especially in the field of power supply. PFISTERER makes a significant contribution to this with its comprehensive product portfolio. To ensure that this continues requires not only the constant development of new, improved and manageable technology but also robust quality control and quality improvement. Even after the events in Japan, the hunger for energy from a continually growing population will not be stopped. This offers us the opportunity for substantial and sustainable growth. The points have been set in the right direction.
Alexander Häfliger nominated as Managing Director Alexander Häfliger, who has strenghened our team since June 2010 as Head of Business Services for the PFISTERER companies in Switzerland, was nominated as Managing Director of PFISTERER SEFAG AG on 1 April 2011. Our warmest congratulations go to him on his promotion and we wish him continued satisfaction and success in his challenging new task.
A Canadian power supplier wanted to know precisely and made an in-depth study of the causes of power failures. The results of the survey in the year 2009: just over 40% of all supply interruptions were caused directly by defective contacts and a further 9.7% had an indirect link to the design of the contacts. A groan goes up from the ranks of the transmission and distribution specialists when Martin Schuster presents the figures. It is no surprise to contact technology expert. «There have been contacts since electricity began to flow into households and businesses. They have done their duty for decades. But for many years now, knowledge of the basic principles and their significance has been dwindling.» There are several reasons. In the past, standard cables dominated the power systems and there was a connection specialist for each type of cable. In recent years, the energy markets have changed rapidly, and with them the energy supply companies. Supply areas have grown together, new cable materials have come to the fore and the growing demand for power has led to ever-larger cable cross-sections. Up to seven different types of cable in a single distribution system is not a rarity. At the
same time, the fitters today have become all-rounders in the utility provision areas of electricity, water and gas. What are needed now are reliable contacts suitable for flexible utilization that can be fitted easily and securely. Technology in change Not a new experience for PFISTERER. The company has based its success on periods of breakthrough. Such as in the 1950s to 70s when aluminium cables largely drove out copper and the company went down new paths in contact technology. Still today, PFISTERER adapts its offer to changes in
Causes of power failures
(2009 study by a Canadian power supplier) 1. Loose contacts or contact parts: 38.3% 2. Moisture: 17.4% 3. Power line malfunctions (all except lightning strikes): 10.4% 4. Defective or inadequate insulation: 9.9 % 5. Foreign bodies / short-circuits: 7.3% 6. Overloading / inadequate supply capacity: 2.4% 7. Deposits of dust, sand and oil: 2.2% 8. All other causes: 12.0%
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the markets and the technology. With its patented SICON screw connectors, for example, the company provides a convincing alternative for uses that permit the conversion from compression to screw connectors. The compression technique does function exceptionally well. But it is the cause of many power failures. The cause: the compression technique is based on fixed parameters. Sleeve cross-sections and tools are specific to each cable crosssection. Cable technologies and markets have now broken these fixed boundaries. The cost of cables increases with each kilometer in length, so cables are produced more efficiently. The individual strands are compressed more tightly and cables become more compact and less insulating material is required. The consequence:
PFISTERER seminars for power system engineers – The contents at a glance • Introduction: increasing load flow = higher risk of failure • Basic principles of contact technology • Mechanisms of the loss of quality of conductor connections • Improvements in the life expectation of contacts • Experience in the field with selected connector designs • Test standards and test procedures Seminars by PFISTERER for practitioners PFISTERER also offers contact technology seminars for practitioners. Focus: products in use and installation know-how. Our staff will be happy to answer any questions you may have on the seminar series under telephone number: +41 41 499 72 72.
what is designated a 95 mm2 cable may have different dimensions in practice. In addition to the various types of cable come new cable cross-sections. Sleeves and tools have remained the same. If the right one is not to hand, another may be used. For work on power grids, time is always pressing . No network without contacts In the meantime, demand for energy has never been higher and the tendency is rising. Networks that are thirty or forty years old are now operating at full capacity . And so Martin Schuster has come to the decisive point in his presentation: the significance of contact technology for security of supply. «Without networks there can be no community, its basis is social contacts. It is no different for electrical networks. They function only as well or as badly as their electro-technical contacts.» Despite higher loads on power systems, the requirements for contact quality vary from country-to-country, as failure rates recorded all over the world demonstrate. The power supply fails for seven minutes per year and end-customer in Germany, in the USA it is already nine hours. Thailand gets it up to even 14 hours and in Bangkok alone there were around 1'500 medium voltage joint failures in a single year. That high quality contacts are worthwhile even in the medium-term has been calculated by the Association of European Cable Set Manufacturers using the «total cost of ownership» method.
Cheap or worth the money? In the determination of the «total lifecycle costs», the price of the product is only one item. To it must be added installation, maintenance and logistics as well as downtime and compensation costs. A product that starts off looking cheap at Euro 50.– with a failure rate of 1 percent produces a total annual cost of Euro 115.–. A higher quality version of the product for Euro 70.– costs only Euro 97.– with the same failure rate. The most cost-effective variant is a product for Euro 90.– and a failure rate of only 0.5 percent for a total cost of only Euro 85.–. Not peanuts, especially if we consider that sometimes equipment worth millions of francs is dependent on a contact that costs Euro 10.–. Not for nothing has PFISTERER traditionally relied on quality – and interprets its knowhow in products as well as in seminars. The latest series of seminars is seen by Martin Schuster, Senior Advisor for PFISTERER, as a commitment to mutual benefit: «Each seminar is also an exchange forum for experts worldwide. So we gain valuable impulses at first hand. And, in the end, we all have the same interest: the security of the power supply.». At the seminar in Melbourne, Australia, the flow of information appeared to be circulating at full speed. One participant departed with the words: «That was the first seminar in ten years whose content we can use immediately in our daily business.». Martin Schuster
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CoC Cable Systems: Dry cable terminations
New generation. More advantages. Time is money. And the environment is a precious asset. Simple insights, implemented by the IXOSIL ESF and EST dry-type cable terminations. Their new generation covers voltage levels up to 170 kV and cable crosssections up to 2'500 mm2. Practical use demonstrates their proven and their new advantages. No question: insulating oils perform their functions reliably. But there is also no question that their use entails a lot of work and brings risks for the environment. That is why, several years ago now, PFISTERER developed unique cable terminations for the sensitive high voltage area. Made up of modular silicone parts which are simply pushed on and bonded together, they are completely free of oil. The flexible ESF can be used for short-term provisional connections. For example, if installations have to be tested during building work or if a provisional or permanent busbar connection has to be made in a substation. Both testing cables and building site cables can be simply and rapidly connected by ESFs with no constructional modifications. The ESF can be installed on the ground on-site or in the workshop. Or PFISTERER can deliver them pre-assembled and electrically tested as IXOLINE. Either or: their flexibility and simple assembly procedure shortens equipment power down-times by a multiple. The maximum length for IXOLINE depends on the cross-section and voltage.
Saving and protecting with purpose EST delivers exemplary figures. Designed for permanent installation, it consists of an ESF and, to date, three insulator elements. If conventional terminations are connected directly to the overhead line, an additional installation staging will be required on the mast and the installation work requires a shut-down time of up to one month. It’s different with the EST from PFISTERER. As with the ESF, fitters can install it on the ground and lift it up to the mast using the cable. Shut-off time for the overhead line: two to three days – with no staging which greatly reduces the cost for the end-customer. The new EST saves even more space as it is fitted with only one insulator. This and its dry construction also permit reliable installation at an angle of up to 30° from the vertical. In the long-term, ESF and EST are equally valuable. Because silicone offers better protection for the environment, people and equipment in case of damage: where there is no oil, there is no risk for nature.
Invest with vision With the attainment of the 170 kV level, now transformer manufacturers can also benefit from the advantages of the flexible ESF in a wider range of voltages. As IXOLINE with a short testing cable and a CONNEX plug on the transformer side, they can test their transformers efficiently in the workshop prior to delivery. There is no longer the need for the costly installation of oil-insulated terminations. Another advantage that makes conversion to the dry, plug-in CONNEX connection system profitable over the long-term. PFISTERER also thinks sustainably. With the launch of the new generation, production has been converted from RTV silicone to LSR and production capacity has been increased. The 170 kV voltage range has successfully passed IEC 60840 type-testing.
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LSO: First Tensorex C+ integrated into Swiss rail network
Constant tension in most compact form The first Tensorex C+ in Switzerland was installed on 11 October 2010. The compact product and its rapid installation procedure delighted the Matterhorn-Gotthard Railway technicians.
The delighted crew from the Matterhorn-Gotthard Railway, l to r: R. Capacchione, H.-R. Isenschmid and a fitter.
were able to install the Tensorex C+ quickly and with no problems. After just three hours, the team leader was able to try out the instructions for the adjustment of the equipment with the PFISTERER specialists on site. The uncomplicated, simple and rapid installation procedure delighted all concerned. The installed Tensorex C+ tensioning device inside the railway gallery at the Oberalp pass.
The Matterhorn-Gotthard-Railway seleced the spring-based automatic tensioning device for the catenary system on the Andermatt–Disentis line at the Oberalp pass in the Calmot gallery at an altitude of around 1'800 m, because of its compact dimensions. The tight space restrictions necessitated fitting the equipment horizontally, instead of the usual vertical installation. The study for this special installation was carried out by Furrer + Frey from Berne. Despite the procedure being new and unfamiliar to them, the two fitters, under the leadership of H.-R. Isenschmid (Team Leader Overhead Lines),
Tensorex C+ – the strength and space wonder The Tensorex C+ is a further development of the patented TENSOREX TR system, which has been in use for more than 10 years and in 20 countries. In contrast to the usual coil spring packages, the equalisation of the change in length of the contact wires caused by the continuous fluctuations in temperature is performed by a spiral spring. The Tensorex C+ thus has a low weight and its very compact construction requires significantly less space, whether installed vertically or horizontally. A glance over the border... There are some other very interesting installation locations for our Tensorex C+ in
the Alpine region. Some years ago in South Tyrol, the over 100-year old Rittnerbahn was equipped with the Tensorex C+ as part of a general renovation. This railway is an electrically-powered 1'000 mm narrowgauge line at Ritten near Bolzano in South Tyrol. The «Bahnl», as the Rittnerbahn is called affectionately by the locals, links the communities of Maria Himmelfahrt, Oberbozen, Wolfsgruben, Lichtenstern and Klobenstein on the Rittner high plateau. René Zürcher
The Tensorex C+ in open-air use with the Rittnerbahn in South Tyrol.
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CoC Components: Development of transformer connection technology
Transformer connections in the past - 2DIREKT Today 2DIREKT transformer connection clamps provide fitters and power system operators with numerous benefits. The basis for this: the improvement of existing technology in response to practical experience.
One of former techniques to connect distribution transformers with the electrical net was as follows: The connection between cable and cable lug was compressed and the junction screwed to the brass flag terminal. Between the cable lug and the brass flag terminal is a copper extension, screwed at both ends. This allows earthing outside the tight housing space. Sounds like a complicated installation. And it was. If you count along, you come to three screwing operations and one compression. A total of four contact junctions per cable, each a potential source of failure with each manipulation. And then the tricks that physics can play. Each contact junction offers resistance to the flow of current, each contact resistance means a loss of performance. And then the complicated overall construction in a tight space, that makes it difficult to avoid accidental contact. The standard to date The fitter and maintenance personnel did everything right. Still in service today, the distribution transformer has served its purpose. But it is still a good thing that we have made progress in the meantime. In the 60s came the shackle clamp, a forged connector piece in brass. An innovation then: The number of contact points was halved, four contact resistances became two, the structure was more compact, the number of variations greater and many fewer manipulations reduced the risk of installation errors. The shackle clamp spread across all markets and was supplied by many manufacturers using the same basic technology with country-specific adaptations. And there were covers to protect against contact
in accordance with IP 2X. Since security against accidental contact has been technically possible, transformers are able to be cleaned while still in operation. Cleanliness for safety in substations cost downtime until then. The practice demonstrates the disadvantages In use, the shackle clamp showed potential for improvement. Fine wire conductors could spread out over the edges of the V-shaped cable bed under the pressure point so that individual strands were lost and full conduction performance was not achieved. The only counter-measure: the fitter stabilised the cable before the contact point with a corset of binding wire or with a wire end ferrule. Disadvantages: the additional supporting structure created a new contact resistance, cost installation time and, as an additional working step, represented a source of error. In an atmosphere containing ammonia, such as close to an agricultural operation, the brass could corrode and split and became brittle until it failed. If the shackle clip is not fully occupied when connected, a plug has to be inserted to fill the empty space in the cable bed. A further additional piece that may not always be available. If it is not used, the screw path may be too long to create the required contact force. Two different clamps are required for horizontal and vertical taps from a transformer. The innovation is in the name Numerous reasons to improve the technology. PFISTERER introduced this to the market eight years ago with the 2DIREKT transformer connection clamp. Its name reveals the technical innovation: the clamp channel and thread drilling
are identical and the conductor can be connected as required horizontally or vertically. The clamp and the screw can be re-used. New application variations can be implemented quickly. Since the launch of the 2DIREKT XL in 2008, as many as six 400-mm2 conductors can be connected directly. In addition to versatility comes better safety during installation and in operation. The body of the 2DIREKT clamp is tinned, the steel screw is galvanised and so both are protected against environmental influences. The patented conductor connection prevents individual strands shearing off. The pressure plate familiar from the SICON screw connector transfers the contact force with no loss to the clamp body while simultaneously protecting the cable against excess pressure. The ideal contact is made even with fine wire conductors – with no danger that they may be damaged. Better. In the future as well. Since 2DIREKT, there is no more compression attachment of cable lugs and wire, sleeves and compression tools are no longer needed. Only two contact points remain, and thus only two contact resistances per connection. Several advantages add up to form the bottom line: less installation work, fewer potential sources of error and, not least, less operational losses from the transformer. But the final chapter in the history of transformer connection technology has not yet been written: «With 2DIREKT, we have set a technology with many advantages against the shackle clamp», PFISTERER Product Mana-ger Hagen Berroth reports, «but experience also shows us that if we keep looking forward, sooner or later we shall see the potential for further improvement.».
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CoC Overhead Lines (OHL) / PFISTERER (Pty): Medupi – Spitskop 400 kV overhead power line project
Twice 192 kilometers of power for South Africa Overhead power lines play an important role in the development of the South African power supply. PFISTERER supplied the 400 kV insulator strings, complete with composite insulators, high voltage fittings and string hardware, to connect the new Medupi Power Station. The new overhead lines will connect the Medupi power station in the north of South Africa to the national grid. Its start-up is planned for 2012. The two 400 kV overhead lines run in parallel over a distance of 192 km, side-by-side in a southerly direction to the Spitskop substation, located 160 km northwest of Pretoria. The order covered the entire 400 kV insulator string, complete with composite insulators and high voltage fittings, spacer dampers and other string fittings. PFISTERER (Pty.) Ltd. also supplied the «stay guys» for the pylons. We also supplied spacer dampers and Stockbridge dampers for a third line, known as Medupi – Marang, which follows the course of
the new line over large parts of its length. Medupi – Spitskop is part of a five-year contract signed in March 2009 to supply equipment to the South African power generator ESKOM. The material for the Medupi – Spitskop line has been delivered and installation is progressing at full speed.
Medupi – Spitskop 1 and 2 Length of line: 2 x 192 km Construction: two single line systems running in parallel Phase conductor: Quad ACSR Tern Guard wire: 1 x ACSR Panther and 1 x 19 / 2.7 mm GSW Wolfgang Huiber/Stephen Smith
The parallel-running Medupi – Spitskop 400 kV overhead power line.
Le p h al al e (Medupi)
Spitskop
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New PFISTERER LSO (Local Sales Office) opened in Beijing
PFISTERER in China: A great step forward The first Asian subsidiary company of PFISTERER Holding AG opened for business in 2010. A significant step for the group: establishment in the booming Chinese market after 15 successful years of doing business there. The core activity of PFISTERER Power Connection Systems Co. Ltd., headquartered in Beijing, is the sales and marketing of all the group’s products in China. The most successful products to date include the products from the competence centres for cable systems and
28.11.2010 – Opening speech by Dr Konstantin Papailiou.
Ribbon-cutting ceremony in front of the warehouse by Dr Konstantin Papailiou and Dr Jost Baumgärtner.
catenary power supply systems. Numerous reference projects testify to their spread throughout the Middle Kingdom. Since December 2010, PFISTERER has also been one of the three leading suppliers for 220-kV cable accessories to the State Power Grid of China. Two of the key parameters for corporate success in China are reaction times and product delivery times. In contrast to most other markets, the country is exceptional in its demand for extremely short delivery times. Whatever happens there happens fast. And a lot happens. Installed generating capacity increased in 2010 to 962 GW, of which 73 percent or 707 GW is generated by combustion. Hydro-electric capacity reached 214 GW, nuclear capacity 11 GW and wind power 31 GW. According to State Power Grid, China is planning to expand capacity by an additional total of 500 GW by 2015 to satisfy the growing demand. That means that every 15 months, the installed power station output in China will rise by an amount equivalent to the entire generating capacity of Germany. The demand for forward-looking technologies is commensurately high – the best conditions for the efforts of the PFISTERER subsidiary in Beijing to flourish. Jan Kuhlefelt A selection of PFISTERER highlight reference projects in recent years:
The lions enter! Let business begin!
Landmark Towers and PFISTERER office entrance.
Beijing airport express line Shanghai EXPO substations Shenyang Olympic sports centre Shanghai Yangshan port (main port in Shanghai) Beijing-Tianjin high speed railway Beijing-Shanghai high speed railway Guangzhou-Hong Kong high speed railway Shanghai-Nanjing high speed railway Shanghai-Hangzhou high speed railway Shanghai Metro line 10 Guangzhou Metro line 1 Suzhou Metro line 1 Hangzhou Metro line 1 Nanjing Metro line 1 Tianjin Binhai development zone Shanghai Jinshan Petro company SinoPec Shanghai Tianjin Beijiang power plant Shanxi Steel works Ningxia Daba power plant
Activity in the Middle Kingdom 1990s PFISTERER products enter the Chinese market in significant quantities for the first time 2004 Sale of the first IXOSIL products in China 2005 Six-fold increase in turnover in China 2006 Opening of the PFISTERER sales office in Beijing, conclusion of the technology-transfer agreement between the PFISTERER catenary power supply competence centre and the XINDI company 2010 Foundation of PFISTERER Power Connection Systems Co. Ltd. in Beijing
Entrance and product exhibition.
Main office.
To ensure rapid delivery times, the company stocks key products and individual components on-site in Beijing.
Installation training, February 2011.
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PFISTERER International: Trade fairs in Asia and the Middle East
Active presence at the heart of the transformer world
Middle East Electricity Exhibition in Dubai, February 2011.
TRANSFORM in Singapore, mid-April 2011 – the leading discussion platform for users and suppliers.
Visitor record for TRANSFORM TRANSFORM, which was held on 19/20 April 2011 in Singapore, set a new highpoint for visitor numbers in the ten-year history of this industry get-together. With 450 guests from 46 countries, more people attended than ever before. Their focus: the exhibits and technical lectures of the TRANSFORM partners MR, Omicron, HSP, Nynas, PFISTERER, Röchling Engineering Plastics, ThyssenKrupp Electrical Steel, Krempel Group, LS Cable-Essex and GEA Heat Exchangers. Under the title «Sustainable Transformer Technology», the range of topics covered at the event stretched from HVDC undersea cables through special steels for energy-efficient transformers, and the significance of connector technology for operational safety to intelligent system solutions for future distribution networks. To an even greater extent than at the previous conference in Rome in 2009, it was evident that TRANSFORM has developed to become one of the leading global platforms for discussion for users, manufacturers and suppliers in the transformer industry. Further information on the event and the TRANSFORM partners can be found under www.transform.net.
Peter Kaiser
Presence at fairs in Dubai and Seoul In February, PFISTERER successfully presented its innovations at the Middle East Electricity Exhibition in Dubai. Two months later, contact was made with more specialists from the Asian area at the INMR
INMR World Congress in Seoul, April 2011.
World Congress in Korea. Organiser of the congress entitled «Insulators, arresters and bushings» in Seoul was INMR, the trade journal for insulator technology.
PFISTERER Holding AG A quarter-century in power
On 1 January 2011, it was 25 years since Dr. sc. ETH Konstantin O. Papailiou joined SEFAG in Malters as a young electrical engineer. With his know-how, never-ending curiosity for things new, wide vision and tireless energy, he made a significant contribution to the development of SEFAG into the «Champions League» of the composite insulator business and to the alltogether impressive development of the company. His career reached its peak in 2003 with his nomination as CEO of PFISTERER Holding AG, accompanied in parallel by his internationally recognised engagement in CIGRE, in which he has been serving
as Chairman of the Overhead Power Lines Study Committee since 2010. Our warmest congratulations to «KOP» and we wish him continued full power! Changes in the board
Dr. Ing. Thomas Klein has joined PFISTERER Holding AG since 1 January 2011 and will become a member of the board on 1 July 2011. Previously, he was Managing Director of PFISTERER Kontaktsysteme GmbH and head of the Center of Competence (CoC) Cable System. Thomas Klein will take over as head of Sales, Production and Technology from Dr. Konstantin O. Papailiou, who will be retiring at the end of 2011.
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On the Design of Composite Insulators from the Perspective of Corona- and Power Arc Protection in AC Grids – Part 1: Corona Protection Corona protection Even in a self-regenerating insulating medium such as air, corona phenomena are generally undesirable as they have the following negative effects: • energy loss • acoustic disturbances (in dry conditions and in rain) • electromagnetic disturbances • light phenomena • ozone formation • damage to string components and insulator housings From a historical point-of-view there are certain rules and standards valid for conventional insulator strings, i.e. for glass or porcelain insulators, which also tend to be applicable for composite insulators. These include IEC 61284 (1st edition 1995), which defines tests for radio interference voltages and corona. Background of the Article The journal «Insulator News and Market Report» by Canadian publisher Marvin Zimmerman appears about six times per year with a mixture of technical and informative articles. Today it has an audience of some 50'000 readers in 200 countries. Every 18 months accompanying symposia concerned with insulators, surge arresters and bushings are staged. This year’s symposium held at the end of April in Seoul, South Korea, was extended to include the thematic area of “Cable Accessories”. The convener of CIGREWorking Group B2.21 (Insulators) and one of this journal’s active columnists was also invited this year as guest speaker on an insulator topic to reflect the current state-of-the-art. This subject was chosen due to its latent topicality and is represented in this article as Part 1 with extracts relating to the corona phenomenon.
Moreover, for composite insulators there are „old“ recommendations by CIGRE Working Group 22.03 (Use of Stress Control Rings on Composite Insulators; ELECTRA August 1992), which were published at the same time as the release of the first product standards for composite rod insulators (IEC 61109, 1st edition 1992). These recommendations can be summarized as follows: • Corona rings are to be installed on the high-voltage side starting from 220 kV, or for lower voltages, when the shank diameter of the composite insulator is less than 20 mm. • When the behaviour is uncertain – today’s simulation processes and computer performance were not available in 1992 – corona tests simulating the insulator configuration (suspension or tension, insulating crossarm) in site conditions are to be performed. The recommendations in this form have so far not been anchored in a standard. As a result, examples and experiences from common practice world-wide have shown that the observance of these recommendations is often not guaranteed. The risk increases when by virtue of a division into insulator and string hardware the responsibility for the design and operational behaviour of the string as a whole is no longer defined. In the worst case there is no check of the maximum electric field strengths occurring on the string and continuous corona discharges during operation are the result. The two following examples are taken from the recent past and reflect the spectrum of possible causes of error which can lead to the inducement of continuous corona discharges with firsttime as well as with long-term users of composite insulators and insulator strings with composite insulators.
These include: • Cost pressure • Poor specification of the on-site conditions • Design errors • Installation errors Example 1 – Double Tension String 525 kV on Lattice Tower The photographs in Figures 1 and 2 were taken by a first-time user of composite insulators on a strategically important 525-kV line using a night-UV camera. The previously used technology was glass cap-and-pin insulators. In Fig. 1 the large shielding rings known as „rackets“ can be seen, which combined as arc protection fittings represent the state-of-the-art for strings with glass cap-and-pin insulators. Today, it has come to be accepted that corona rings are seen as a part of the composite insulator, and are included in its scope of delivery. This results from the fact that there are philosophies among certain utilities, often encountered in the USA, not to implement any arc protection devices. Problems develop as in this case, when the corona rings are forgotten Racket
Silicone insulators Fig. 1: Photograph of insulator string with external light.
Continuous Corona
Silicone insulators Fig. 2: Stable corona discharges on both insulator fittings on the high-voltage side of the double string.
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Fig. 5: Photograph mit daytime-UV camera.
Fig. 3: Corona test on 525-kV double tension string.
Fig. 6: Retro-fit with corona rings, no repair of damage.
during installation or do not fit into the existing string. A retrofit of the strings with corona rings has been implemented in the meantime and selected composite insulators with this implementation history have been removed for detailed inspection. In this case it was primarily the composite insulators with corona rings in a suspension and tension configuration that had been successfully type-tested, including a corona- and interference voltage evaluation (RIV = Radio Interference Voltage). Corona starts at the corona rings (Fig. 3), at a value lying about 18% above the level of the highest conductorearth voltage (Fig. 4). That proves that the critical sealing area at the so-called triple point between insulator fitting, sealing interface/core and the surrounding atmosphere is shielded and released from stress as desired. The RIV-value of 45 dB/μV at 333 kV was also complied with (46 dB/μV was specified, dashed line – – – –).
degree of pollution in the operational area, an intensive gray colouring in the first part of the shank was detectable, apparently the result of an oxidation-stimulated crosslinking leading to the formation of SiOx on the silicone rubber surface. The locations of the damage on each outward facing area of the fittings of the left and right hand insulators in the double string is due to the fact that the field-controlling effect of the racket is lowest at these locations, the field strength therefore is at its highest. The insulators were retrofitted with corona rings, which eliminated the corona, but could not repair the damage to the sealing system (Fig. 6). The removal of damaged insulators and the detailed analysis of the affected sealing area showed that without additional measures there was a risk of additional accumulation of damage. For this reason all the composite insulators were replaced and the string design was adjusted. The cause of the failure was that in this case the string had not been tendered as a complete package, but as individual components. The requirement for a full system type test, in which the design error would have been easily recognizable,
Example 2 – 245-kV-Double Tension String at Substation Entry Point This example shows the photographs taken with a daytime-UV camera (Fig. 5) in a Europaen 245-kV substation.
Corona extinction voltage
Fig. 4: Trace of interference voltage and value of corona extinction voltage.
Typical for this camera system is the portrayal of corona discharges as integral «measurement clouds», the form of an individual discharge and its precise position cannot be resolved. The presence of the measurement cloud shows without doubt, that the string design has not been adapted to the voltage level. The upward-oriented racket is clearly visible as the only arc protection device, which due to its position and geometry is not able to provide a complete corona protection function. As a result of this and after an average period of operation of little more than a year, considerable damage to the galvanizing and to the sealing system in adjoining areas was identifiable (Fig. 6). Furthermore, in spite of a low
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had been waived. Are the above-mentioned design recommendations adequate? This question can be answered with a «yes» and a «no». If a composite insulator or string can be proved corona-free in tests or in a simulation, then a critical, operationally relevant cause of damage can be ruled out because these discharges from a steel component would exist on a continuous basis. On top of this, the phenomenon of water drop corona due to the very favourable hydrophobicity of polymer insulating materials needs to be considered. Scientific investigations in Germany and around the world have shown that when a certain field strength on the surface of the insulating material is exceeded, the high coefficient of permittivity of water relative to air (80:1) can cause deformation of the drops and the firing of discharges at their deformed ends. In unfavourable conditions decomposition products are formed, which can result in failure when the materials used in the composite insulator have been improperly chosen (cost pressure). Due to negative experiences of this problem in the USA (more than 30 failures), a working group of the IEEE (Institute of Electrical and Electronics Engineers) has responded with a systematic compilation of operational experience and the correlation with simulation results and has derived corresponding recommendations. These have been published in an IEEEpublication and can be summarized as shown in the table below. It is recommended that simulations be performed as certain electrical field strengths are very difficult to detect by Occurrence of Corona
Duration
Dry conditions
continuous
Wet conditions
discontinuous
Wet conditions Dry and wet conditions
discontinuous continuous / discontinuous
Part of the Insulator String
Corona- or combined arc protection ring, insulator fitting Insulated housing at shank Sealing interface* In insulator (rod, insulating coating, interface of the two)
measurement. For this, methods such as finite element or boundary element calculations are suitable. Thanks to the computer speed and performance now available, these can even be carried out three-dimensionally with consideration of neighbouring phases, which increases the accuracy of the results. The insulating crossarm in the Randstad 380 compact transmission line presented in Connect 1/2010 was simulated in this way, as there was a project-specific requirement to limit the maximum value of the electrical field strength to only 2.5 kV/cm (recommendation 4.5 kV/cm) on a length of only 10 mm on the insulator shank. This requirement was seen as«very athletic», as at the same time the aesthetic appearance of the insulating crossarm was aiming to be «soft, non-technical». Conclusion As early as 1992 basic rules for the avoidance of corona discharges on composite insulators and strings with composite insulators were formulated, and rigid compliance to these could have avoided a series of failures. A further contribution to an increase in reliability is brought by not exceeding the maximum field strength on the insulator shank defined specifically for composite insulators on the basis of scientific investigations and operational experience. The given value of 4.5 kV/cm may be regarded as safe in a conservative sense. Examination of SEFAG insulators after a 10-year period of operation in a 420-kV grid have shown that with highgrade materials this value can be exceeded without compromising the operational reliability. Dr. Frank Schmuck
Threshold of Maximum Field Strength in kV/cm ≤ 17**…21
≤ 4.5 on a length of less than 10 mm 3.5 ≤ 30
Long-service anniversary of Manfred Peter On 1 April 2011, Manfred Peter, Managing Director of PFISTERER INTERNATIONAL AG, celebrated 40 years of service with PFISTERER. He can look back on an extraordinary, long and successful career. • 1.4.1971: joined KARL PFISTERER Elektrotechn. Spezialartikel GmbH & Co KG in the Foreign Sales department. • 1.1.1982: Sales Manager for SEFAG EXPORT AG. The objective of the job: he had the task of using his technical knowledge and his personal contacts to identify, develop and initiate activities in new markets for the export business and to undertake all the steps necessary to achieve this in the most cost-effective manner for the company. • 1.11.2003: took over the function of head of Sales and Marketing as Director International Sales in the international business of the Swiss PFISTERER companies. In this function, he was and is a member of the Executive Board. • 1.7.2010: appointed as Managing Director of PFISTERER INTERNATIONAL. We congratulate Manfred Peter warmly on this service anniversary and wish him continued satisfaction and every success in his efforts on behalf of PFISTERER customers all over the world.
Publisher
Connect International
Verification by Test in dry conditions x
Simulation in dry conditions x
–
x
– –
x x
* For insulator designs having an exposed sealing interface, the so-called overmolding of the fitting or the use of a corona shield does not apply. ** For highly corrosive environments, as the corona inception voltage can be reduced by rust formation.
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Magazine for customers of the PFISTERER companies in Switzerland and South Africa – 18th year – No 1/2011 – published twice a year Print run: 1200 copies Coordination: Barbara Simeon PFISTERER SEFAG AG Werkstr. 7, 6102 Malters Tel.: ++41 41 499 74 79 Fax: ++41 41 499 74 26 Mail:
[email protected] Final editing/layout: Brigitte Senn, www.amk.ch Printed by: Engelberger Druck AG Closing date for 2/11: 30.09.2011
