Bushing: Bushings Factory Places Focus on RIP Technology
BUSHINGS
20
YEARS
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INMR Issue 99.indd 76
Q1 2013
“Bushings are one of the most critical components in any power network since all energy flows through them and they must be able to withstand the resulting electrical stresses.�
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Bushings Factory Places Focus on RIP Technology
W
hen it comes to bushings, resin impregnated paper (RIP) technology shares a number of characteristics with composite hollow core insulators. Both are considered comparatively advanced technologies in their fields from the standpoint of performance and safety. Both have now been available for decades, with a well-documented record of success across many applications. But, in spite of the above, both have yet to reach the lofty market penetration levels expected of them in their early years. On this last point, there is yet another interesting similarity: in a very conservative industry, they have had to compete head-on against established technologies, namely porcelain and oil-impregnated paper (OIP) designs – both long trusted industry stalwarts and also usually less costly than the technologies seeking to displace them. INMR visits HSP Hochspannungsgeräte GmbH, part of the HSP & Trench Bushing Group, to report on why this factory concentrates only on RIP styles and how it views some of the challenges ahead when it comes to bushing designs and applications.
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Photos: INMR ©
RIP bushing production begins with crucial step of winding crepe paper with precisely placed metal foil inserts onto conductor core, followed by drying to remove trapped moisture.
HSP has a long history in the area of bushings, with its forebear, Felten+Guillaume having been one of the early pioneers in breakthrough technologies such as molding silicone housings directly onto RIP cores. HSP (known in the past as HSP Hochspannungsgeräte Porz and once also offering OIP technology) was also one of the first suppliers to develop its own composite-housed RIP designs – still regarded by many as the state-of-the-art when it comes to bushings.
In recent years, however, the bushings industry has undergone much consolidation, with three engineering giants – ABB, Siemens and Alstom – currently estimated to share some 60 percent of the total market. In the process, HSP now finds itself part of a large corporate structure (HSP & Trench Bushing Group) that has greater capacity for OIP types than for RIP. Alexander Doutrelepont, V.P. Sales & Marketing of the Group, is based at the HSP factory in Troisdorf,
Germany, just south from the original location near Cologne. This modern facility, completed only in late 2007, now concentrates solely on production of the RIP design. Doutrelepont explains that the bushings business is perhaps best described using a triangle involving the end user, the electrical apparatus OEM and the bushing manufacturer. While it is OEMs such as transformer manufacturers that do the ordering and buying in most cases, their focus tends to be on short-term procurement issues including price, delivery and meeting the basic required standards. It is the end user that is usually more concerned about long-term properties and performance or whether a unit is equipped with a porcelain or silicone composite housing. Doutrelepont emphasizes that, in spite of this division of interests, everyone in the industry recognizes that bushings are among the most critical components in a power network. All energy must flow through them and they must therefore be capable of withstanding
RIP transformer bushings at ± 800 kV Suidong Converter Station in southern China.
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Photos: INMR ©
Impregnation of dried crepe paper core with resin takes place over several weeks in cylinders up to 13 m deep. Temperature profile must be carefully controlled to ensure complete absence of voids or cracks.
the resulting electrical stresses. At the same time, he sees a fundamental changeover now underway in the power engineering field that will require educating a new generation of engineers about such challenges. “As more and more specialists in this area approach retirement,” he says, “we see a growing role for bushings suppliers such as ourselves to help train end customers about their equipment and its environment.” One of the biggest surprises in the power supply business, according to Doutrelepont, is just how quickly the industry moved to UHV, a trend he claims few foresaw. “Less than 10 years ago,” he remarks, “hardly anybody thought 800 kV or 1000 kV. Yet over a relatively short time frame, our industry has had to develop, test and manufacture bushings for these voltage levels. It has been a significant milestone that we were able to do it.” Indeed, it was the sudden ‘explosion’ of interest in UHV that provided an internal justification for the investment to build an entirely new factory in Troisdorf. Doutrelepont estimates the annual world HV bushing market at approximately US$ 800 million, growing steadily at about 3 percent annually until recently, when increased price pressures have made it more volatile. If anything, this new uncertainty has only added to what Doutrelepont sees is a requirement for a basic shift in the manufacturing landscape. “In our Group,” he explains, “we have recognized the need for better aligning products so as not to have all technologies available in any one factory. That’s simply not efficient. Rather, it is better that each production site focuses on its strength.” In the case of the HSP & Trench Bushing Group, this strategy has, for example, resulted in the factory in France specializing only in OIP.
Doutrelepont believes that the related decision to concentrate only on RIP technology at the HSP facility and to transfer all former OIP production to the French factory was also the correct one. “The main goal of specializing in only one type of bushing at each factory,” he says, “was to avoid having duplicate sets of experts and machinery on site, each focused on basically different technologies and processes. We are one of the few in the industry to have already completed such a re-alignment and we hope it will now make us the most cost efficient.” Still, in spite of this renewed commitment to RIP technology in Troisdorf, the pace of the market transition away from OIP bushings is not as rapid as most in the industry had predicted years ago. Back in 1993, RIP styles were estimated to account for only 5 to 10 percent of total bushing sales worldwide. Today, while RIP has clearly grown in popularity, its overall market share still hovers at a figure of less than 30 percent. OIP clearly remains the dominant bushings technology with some three-quarters of the business. These comparative proportions, of course, vary by country with RIP being relatively more used in Europe whereas markets such as China, India and Latin America overwhelmingly favor
“Only 10 years ago, hardly anybody thought 800 kV or 1000 kV. Yet over a very short time frame, our industry has had to develop, test and manufacture bushings for these voltages. It has been a significant milestone that we were able to do it.”
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OIP types. The U.S. bushings market is also dominated by OIP styles but Doutrelepont notes that RIP has finally begun to gain a foothold, especially along the West coast due to seismic and other concerns. “We see that the market is increasingly demanding RIP types,” insists Doutrelepont, “especially as end users become aware of their performance advantages.” He mentions as example problems that recently occurred with OIP bushings at a major hydroelectric project in South America due to very fast transients (VFTs). In applications such as hydropower, sudden huge load shifting due to heavy peaks and switching operations create these VFTs and it is not uncommon to have electrical breakdown of the bushing by puncture, with associated risk of explosion and fire. The solution in such applications, according to Doutrelepont, is applying RIP technology, which he claims is more resistant to the stresses from VFTs due to internal resistive grading.
Photos: INMR ©
One of the factors recently impacting the bushings business, notes Doutrelepont, is the economic slowdown both in developed and developing countries. This has followed a sustained period of growth during which many transformer OEMs built up capacity and has therefore resulted in more intense competition. Delivery times
for large power transformers are now measured in only months rather than years and this has placed added delivery pressure on bushing suppliers. “Typical lead times for bushings up to 245 kV are now some 6 to 10 weeks,” he says, “and only 12 to 16 weeks for units up to 500 kV. This is completely different from 5 years ago when lead times were usually four to five months.” Doutrelepont goes on to note that while there is clearly a need for more power lines to satisfy an electricity hungry world, new projects are increasingly being controlled by commercial people at independent power producers who look at return on investment as the major decisionmaking criterion. This means that there is sometimes too much emphasis placed on short-term cost reduction and not enough on preventing the emergence of problems over the long term. Another related issue, according to Doutrelepont, is that some utilities are looking for ways to extend the service life of transformers that used to be routinely replaced every 40 or so years. Both of these factors end up putting more pressure on bushing prices. What can bushing suppliers do in the face of such delivery and cost pressures? Doutrelepont believes one solution lies in greater standardization and also in better agreements with subsuppliers of key components such as insulators, castings and mechanical parts. Apart from contributing to shorter delivery times, such agreements could also offer added opportunities to lower costs such as by standardizing housings. “One of the main challenges in our industry today,” he states, “is reducing costs by standardizing creepage at e.g. 31 mm/kV. This would mean that insulator manufacturers could focus on equal, repeating items in high volumes while at the same time allowing
Impregnated cores undergo machining to precise tolerances on CNC machines.
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“New power projects are increasingly being controlled by commercial people at independent power producers who look at return on investment as their key decision-making criterion. This means that there is sometimes too much emphasis placed on short-term cost reduction.”
±800 kV RIP wall bushing being prepared for final testing before shipment to customer in China.
the ageing of paper in the core – something that occurs more rapidly with OIP types than when the paper is cured in resin. New synthetic replacements are therefore under investigation by the industry, including polyethylene and silicone films. “A combination of synthetic fibers and resin might improve electrical performance,” observes Langens, “however could also involve some compromise when it comes to mechanical properties. Another issue involves the materials used between the core and the external housing. Currently, polyurethane foam and SF6 are the normal options with the foam apparently growing in popularity. However, as voltages go to 500 kV and beyond, the foam adds significant weight and cost and therefore gas is preferred. Given Photo courtesy of HSP & Trench Bushing Group
the bushings industry to offer products that fulfill all the typical requirements.” Looking to the future, Doutrelepont and V.P. Technology, Achim Langens, see even more challenges ahead, including meeting ever higher performance requirements by using different materials. For example, Langens sees a growing need for bushings capable of operating continuously at high temperatures due to the greater losses normally encountered at UHV levels. The potential risk in this case is that increasing temperatures accelerate
New 1100 kV dry type bushing during testing in August 2012.
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Final assembly of RIP bushings at HSP (these as replacements for Russian transformers) is divided into two areas, one devoted exclusively HVDC.
more and more restrictions on use of SF6, other options are also being considered including mixing foam with gases such as nitrogen to create a softer material with less weight. Insofar as choice of housings, Doutrelepont emphasizes that HSP does not try to impose any insulator technology on customers but rather only recommends what solution is best for the application. Still, he notes that silicone composite housings have been growing steadily in use and indeed are now used on the majority of bushings made at the Troisdorf factory. In fact, he also remarks that other factories in the group are also seeing growing demand for silicone housings – even for OIP styles – mainly to avoid risk of damage from porcelain shards in the event of explosive failures.
Insofar as higher and higher voltage levels, 800 kV DC bushings are now at least 10 m long depending on application and transport considerations make getting them to the installation site a growing problem. Simon Balbierer was the Siemens Project Manager responsible for completion of the UHVDC substation at Chuxiong in south China (see INMR Q4, 2009). This substation, energized in Dec 2009, was the world’s first to operate at 800 kV and has apparently been running at maximum power for nearly the past year. According to Balbierer, delivering the 22 m one-piece wall bushing represented a logistical challenge and required extended lorries to transfer the unit to the nearest German seaport. At the other end, located in a remote region accessible by winding mountain roads, the problems would have been even greater had a rail link not been completed close to the final destination.
Photos: INMR ©
One item that remains to be resolved when it comes to housings, remarks Doutrelepont, is the need to be more specific on their required performance when it comes to seismic, temperature cycling and pollution considerations or during events such as sandstorms. “These types of properties are still not specifically mentioned in IEC standards,” he notes, “and at the same time our industry has to yet to establish a standard creepage that might fulfill almost all requirements.”
Yet another issue for the industry, according to Langens, is that currents are now increasing to 5000A and it is a challenge to offer 800 kV, 5000A bushings, especially since these are being stressed by more and more VFTs. This, he points out, is another motivation to replace crepe paper with synthetic polymers since they offer smoother surfaces without pits or dents.
Greater standardization of specific creepages could help reduce cost of insulator housings. 84 INMR Issue 99.indd 84
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FRP tube of bushings with internal SF6 insulation needs added liner to protect resin material against attack by the corrosive gas.
Going to 1100 kV will be the next looming challenge for bushing manufacturers, predicts Langens. “There were more problems than we initially expected during testing of a 12 m long transformer bushing,” he reports. “The main challenges in this respect will be mechanical aspects, which become even more critical at such
voltages than are the electrical characteristics. It was indeed a surprise how fast we were able to move from 500 kV to 800 kV – and in so many different countries. But going successfully from 800 kV to 1100 kV, that will probably take much longer.”
Interior RIP wall bushing at ±800 kV Chuxiong converter hall. RIP bushings on spare transformer.
Silicone-housed RIP bushings (foreground) await final production step (bottom). Photos: INMR ©
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