Ageing Detection of Metal Oxide Surge Arrester using Fifth Harmonic Resistive Current

Leakage current based condition monitoring plays a vital role to predict the malfunctioning of Metal Oxide Surge Arrester (MOSA) due to its ageing and degradation. The change in the resistive leakage current and particularly its third harmonic component is considered as an excellent indication of arrester's ageing. The presence of third harmonic in the grid's voltage affects the extraction of third harmonic resistive current. Therefore, it can lead to incorrect condition assessment of MOSA. This paper aims to introduce a new ageing indicator for MOSA, which is independent of voltage harmonics. This analysis is performed experimentally on three aged samples of 120kV rated polymeric MOSAs manufactured by ABB. Fast fourier transform (FFT) is applied to the acquired resistive leakage current to extract its harmonic parameters. It is found that the fifth harmonic resistive current exhibits similar sensitivity towards ageing as compared to the third harmonic resistive current. Results have shown that the condition assessment based on third harmonic current can easily be replaced with the fifth harmonic current.