A virtual bridge to compute the resistive leakage current waveform in ZnO surge arresters

The measurement and the harmonic analysis of the resistive leakage current present is an efficient parameter for determining the degradation level of metal oxide surge arresters. In this paper, the methodology and results of a novel circuit for measuring the resistive leakage current in metal oxide surge arresters is described. The technique requires the digital acquisition of the voltage applied to the surge arrester and the total current of the arrester. A virtual bridge has been implemented in software Matlab^® to eliminate the capacitive component. In this implementation the resistive leakage current waveform is computed without the need for an expensive high voltage capacitor. The implementation suggested in this paper agrees well with measurements obtained with a coupling capacitor.