Online Condition Monitoring Technique for Metal Oxide Surge Arresters Based on Leakage Current Components

Metal Oxide Surge Arresters (MOSA) are connected in the system for protection of power system against over voltages. MOSA behaves as an insulator under normal working condition and offers conductive path under over voltage condition. Zinc oxide elements (ZnO Blocks) having non-linear voltage-current characteristics is used in construction of MOSA. Ageing effect under various operating conditions such as pollution, moisture ingress caused degradation of MOSA. Degradation of zinc oxide elements increase the leakage current flowing through it which can create thermal runaway conditions for MOSA. Once, it reaches to thermal runaway condition cannot return to normal working condition results in premature failure of MOSA. As MOSA constitutes a core protective device for electrical power system against transients. Condition monitoring of surge arresters should be done at periodic intervals. Online condition monitoring techniques are much popular. This paper presents the evaluation technique for MOSA based on the leakage current analysis. Maximum amplitude of total leakage current (IT), Maximum amplitude of fundamental resistive leakage current (IR) and maximum amplitude of third harmonic resistive leakage current (I3rd) have been analysed as indicators for surge arrester condition monitoring. The ratios of these leakage current has been evaluated for to access the condition of MOSA. The obtained results are validated with other condition monitoring tests.