Research on aged interfaces of composite insulators after extended water diffusion tests

Over the years, several abnormal fractures of composite insulators had occurred in southern China, with the poor interface quality being regarded as the main reason of this kind of accidents. In this research, an improved water diffusion test method was proposed. We carried out 100-300 hours' water diffusion tests on the insulators which were new or had been operated for different years or abnormally heated, and the variation situation of adhesion during boiling process has also been analyzed. Besides, a microscopic analysis on superficial core material of aging insulators has been conducted to study the aging mechanism of interface. According to the analysis results, 300 hours' water diffusion test was proved to be able to screen out the samples with poor adhesive property or hydrolysis resistance. It was more effective compared with 100 hours water diffusion test which has been recommended by existing standards. According to our observation, there was a significant corresponding relationship between the results of 300 h water diffusion test and the variation of adhesion during boiling. In general, the water diffusion and microanalysis of abnormally heated insulators indicated that for insulators fail to pass the 300 h water diffusion test, hydrolysis was an important reason leading to interface quality reduction.