Frequency characteristics of leakage current for monitoring silicone rubber insulator in cold-fog conditions

Long-term cold-fog condition is presently one of the main causes of the flashover fault of outdoor insulators. To monitor the surface performance of silicone rubber (SIR) insulators in such conditions, an artificial salt-fog test was carried out to investigate frequency characteristics of the leakage current by utilizing a wavelet transform technique. The leakage current was separated into the low-frequency components with the conductive currents, the intermediate components with the transition performance and the high-frequency components with the discharge activities. The related cumulative charges of different frequency components were calculated to show that the high-frequency components and the low-frequency components have the same increasing tendency with the increase of the relative humidity, while they have the reverse tendency with the effect of the ambient temperature. It is suggested that the high-frequency components are more effective than the low-frequency components for monitoring the insulator performance in cold-fog conditions.