New method for measurement of the resistive leakage currents of metal-oxide surge arresters in service

Various methods of determining the condition of zinc oxide (ZnO) surge arresters by means of measuring their leakage current are discussed. A method that minimizes the influence of harmonics in the system voltage when performing a harmonic analysis of the arrester leakage current presented. The presence of harmonics in the voltage has presented a great problem to earlier methods based on harmonic analysis, since these harmonics may interfere with the harmonics generated by the nonlinear resistance of the arrester. The favorable effect of the method presented is achieved by introducing a field probe which allows a compensation for the harmonics in the voltage. The main advantage of the new method is the low sensitivity to harmonics in the system voltage