Leakage current analysis for predicting flashover in distribution network

Flashover process on outdoor insulator is believed to be the interaction of the non-linear arc characteristic with the linear resistance of the pollution layer. Such a complex problem results in great difficulty of obtaining reliable performance of the insulator. Flashover mechanism of outdoor insulator is commonly referred to Obenaus theory in which dry band is firstly formed in the contaminated surface. The voltage drops in such band will create partial discharge in surrounding air and finally lead to ultimate flashover. Just prior to flashover, the leakage current increases in non-linear way, especially with the severity of contamination layer. In this work, a leakage current acquisition system is specifically developed for polluted insulator using in distribution network (35kV). Leakage current waveforms are measured with different amount of contamination on two types of insulator: glass and silicone rubber insulator. Partial discharge phenomena prior to flashover are well observed by the non-linearity of the leakage current. The results could provide a valuable tool for maintenance planning of the insulators in distribution network, especially in industrially polluted or coastal areas.