Medição e análise harmônica da corrente de fuga resistiva em varistores de ZNO.

Abstract

The measurement and the harmonic analysis of the resistive leakage current is an efficient technique for determining the degradation level of metal oxide surge arresters. The arrester consists of a stack of nonlinear resistive blocks known as varistors. A novel technique for determining the resistive component of the leakage current of ZnO varistors has been presented. It consists of a virtual bridge that does not require a high voltage coupling capacitor. The proposed technique has been applied to monitor the resistive leakage current of ZnO varistors that have been degraded under controlled conditions. The degradation has been obtained by applying high voltages and high impulses current discharges. The resistive waveform has been measured before and after the degradation of the varistors. Measurements and simulations are presented and they show that the 3rd harmonic component of the resistive leakage current is a good indicator of the level degradation of the ZnO varistors.