Ageing characteristics of porcelain suspension insulators for transmission line by cool and heat accelerate method

The suspension insulators are subjected to harsh environments in service for a long time. Long-term reliability of the insulators is required for both mechanical and electrical performances. This study described some basic performance test and accelerated ageing test by cool-heat cycling methods and thermal mechanical performance test methods on alumina porcelain insulators (new and aged) used for transmission line in KOREA. In case of aged porcelain, the failure in basic performance tests happened in cool-heat tests. Based on this characteristic, we studied the method predicting failure phenomena through more severe accelerated cool-heat ageing. Results on leakage current and tangent loss after accelerated cool-heat ageing showed that there was some damage effects by thermal shock in the porcelain insulator with cristoballiet body. It cannot avoid damaging from mechanical and thermal shocks, but insulator body with the matrix reinforced with crystalline phases such as alumina and mullite have advantage over the suppression of radical crack advance. From the accelerating thermal mechanical performance test, it was indicated that sample A was more severely damaged by thermal mechanical stress than other samples.