Brittle fractures, on the other hand, occur mostly near the interface between the insulation material and the end-fitting, and provided this area has been properly manufactured, the probability of their occurrence will be lower than that of electrical aging. To estimate service life from the electrical aspect, actual-scale composite insulators were exposed to electrical stress, and were subjected to an exposure test under a natural environment. A test chamber simulating environmental stress was also constructed, and accelerated tests were carried out according to international standards (IEC 61109 Annex C). Further, by comparing leakage current waveform and cumulative charge, which may be characterized as electrical aging, evaluation of composite insulator service life was carried out. Furthermore, since in Japan, a drop in insulation performance due to rapid pollution during typhoons is a familiar henomenon, an investigation was made based on the characteristics of leakage current obtained during a typhoon into the effect of rapid pollution on electrical aging in composite insulators.
Composite insulators are light in weight and have demonstrated outstanding levels of pollution withstand voltage characteristics and impact resistance, and have been widely used as inter-phase spacers to prevent galloping.
They have as yet, however, been infrequently used as suspension insulators. The composite insulators for suspension use that were developed in this work have been proven, in a series of performance tests, to be free of problems with regard to commercial service, and in 1997 were adopted for the first time in Japan for use as V-suspension and insulators for a 154-kV transmission line. To investigate long-term degradation due to the use of organic insulation material, outdoor loading exposure tests and indoor accelerated aging tests are continuing, and based on the additional results that will become available, work will continue to improve characteristics and rationalize production processes in an effort to reduce costs and improve reliability.
5. WORLD LIST
ethylene propylene rubber
ethylene propylene diene methylene
a core of fiber-reinforced plastic
to bear the tensile load
penetration of moisture
AC railway service
malleable cast iron
absence of adequate data
electrical weak points
To possess long-term tensile
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Huntsman: Polymer insulating materials and insulators for high
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greater than 1000V: Definitions, test methods and acceptance
criteria, IEC61109, 1992-03.
3) Guide for the selection of insulators in respect of polluted conditions,
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of leakage current on composite insulators, 4th
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5) Nakauchi et al.: Natural environment exposure tests and accelerated
aging tests of silicone rubber insulators, High-voltage
Symposium, IEEJ, HV-97-41, 1997. (in Japanese)
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High-voltage Symposium, IEEJ, HV-98-73, 1998. (in
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accelerated aging tests of silicone rubber insulators, Proceedings
of Electric Energy Workshop, No. 431,1997. (in Japanese)