Ageing Classification of Metal Oxide Surge Arrester Using Its Power Factor

The third harmonic component of resistive leakage current is considered as the most sensitive ageing indicator of metal oxide surge arrester (MOSA). It is essential to extract the resistive component of the total leakage current prior to determining its third harmonic content. Several methods have been proposed so far to determine the resistive leakage current. But, the implementation of complex mathematical procedures has made these techniques difficult and less accurate. Therefore, this paper is aimed to propose the power factor as a new ageing indicator of MOSA. New indicator is determined without extracting the resistive component of the total leakage current. This study has been performed experimentally on three aged samples of 120 kV rated MOSAs to determine their power factors. The results have shown that the variation in proposed indicator towards arrester's ageing is similar to that of the resistive third harmonic component. The percentage rise in the power factors of MOSA-I, II, and III by increasing the voltage from 70kV to 120kV to simulate ageing, are found to be 105%, 118%, and 108% respectively.