Examinations of ZnO-varistors in the leakage region with regard to high frequency stresses

ZnO-varistors and ZnO-arresters are widely used for protection of HVDC-systems and switch-mode power supplies. Because of high frequency components in the leakage current, a model of the leakage region of a ZnO-arrester is of interest. An equivalent circuit model for the leakage region of a ZnO-arrester is set up. The model is able to describe the frequency, current and temperature dependency of the arrester in the leakage region. The lumped parameters of the model is achieved from tests with frequency sweep analysis, FFT-analysis and DC-resistance measurements at different temperatures. The method for determination of the lumped parameters of the equivalent circuit model is verified by tests on a ZnO-varistor, and the validity of the parameters is tested by parametric simulations. The set up method gives stable parameters and it is possible to simulate a measured voltage with high frequency components from a measured current signal with reasonable accuracy