Investigating the failures of defected silicon rubber insulators in salt-fog chamber

Due to work under complex stresses, the accurate lifetime estimation of polymeric insulators is not easily feasible. Most of polymeric insulators are not able to withstand the electrical and mechanical stresses in the last years of servicing because of ageing. Therefore, the aged polymeric insulators cause many failures along the power network lines. However, investigating those groups of polymeric insulators, which are threatened by ageing, can help to diagnose and estimate the lifetime of them. In this paper, two groups of 20 kV silicone rubber (SR) insulators were tested in a salt-fog chamber, and their performance were evaluated by analyzing their leakage currents. A sample from each groups was defected manually by eroding its housing and cutting its sheds. Also, the performance of new sample and that of manually aged was studied through the low-frequency analysis of their leakage current harmonics. The results show a decreasing pattern for the 3rd and 5th harmonics for the defected samples, and in contrast, an increasing pattern for that of healthy.