A Novel Technique For Condition Monitoring Of Metal Oxide Surge Arrester Based On Fifth Harmonic Resistive Current

The ageing in metal oxide surge arresters (MOSAs) is monitored by measuring their leakage current parameters. Particularly, the third harmonic component of resistive leakage current is directly correlated with the ageing and degradation of the arrester. However, the third harmonic of resistive current (I-R3rd) is also affected by the third harmonic component in the grid's voltage. Therefore, I-R3rd based monitoring may lead to an inaccurate condition assessment of MOSA when the supply voltage comprises third harmonic content. Hence, this paper introduces the fifth harmonic of resistive current (I-R5th) as a new ageing indicator for MOSA. This study has been done experimentally on five samples of aged polymeric MOSAs rated at 120kV. Results have shown that the IR5th exhibits similar sensitivity towards ageing as compared to the I-R3rd. Additionally, it has been found that the variation in I-R5th with the fifth harmonic voltage is smaller than the variation in I-R3rd with the third harmonic voltage. Therefore, the following technique can support the online condition monitoring of MOSAs in a more realistic way than the existing third harmonic current measurement technique.