Failure analyses of nonceramic insulators. Part 1: Brittle fracture characteristics

Nonceramic insulators, also referred to as composite, polymer or polymeric insulators, are used in overhead transmission lines with line voltages in the range of 69 to 735 kV. Despite the many benefits that nonceramic insulators offer in comparison with their porcelain counterparts, they can fail mechanically in service by rod fracture. One of the mechanical failure modes of the insulators is a failure process called brittle fracture, which is caused by the stress corrosion cracking (SCC) of the GRP rods. The process is catastrophic and unpredictable, leading to the drop of energized transmission lines. The most important characteristics of the brittle fracture process, which can occasionally affect high voltage nonceramic transmission line insulators, leading to their catastrophic in-service failures, have been presented in this article. In addition, several experimental techniques were suggested for the simulation of brittle fracture under laboratory conditions. Only the most important aspects of brittle fracture process have been discussed here.