The influence of alumina trihydrate filler on the leakage current in a salt-fog test for polymeric material

Alumina trihydrate (ATH) is usually added as a filler in polymer insulators in order to raise tracking and erosion resistance. Crystalline water in ATH can be evaporated by heat and reduce internal oxidation to polymer and therefore this should suppress carbonization and erosion for them. However, there has been reported that there is a frequent phenomenon in a discontinuous salt-fog ageing test, i.e., the leakage current does not flow in the inception of each cycle of salt-fog test. It is considered that the chemical change of ATH might influence this situation. Therefore, in this study, the alumina component of filled polymeric material was investigated using X-ray deflection method in and after salt-fog ageing test. As a result, the ATH spectrum was intensified in the inception of each ageing cycle, and after that it decreased with elapsed time.