The Changes of Electrical Properties of ZnO-based Varistors Initiated with Current Pulses

Electronics used in various industries and household appliances is threatened by the overvoltage. The protection of electrical equipment against the effects of the overvoltage is provided by the surge protection devices. The ZnO-based varistor represents an important element used in surge protection devices. In this paper, we focus on the degradation effects of current pulses to ZnO varistors. Standard current pulses 8/20 shape were applied to varistor samples of commercial production. The electro-physical properties of ZnO varistors were monitored by measuring the current-voltage characteristic and the dielectric parameters by the spectroscopy in the frequency range from 20 Hz to 2 MHz. It refers to the temperature dependence of the ZnO varistor's current-voltage characteristic in the leakage current region and to the reduction of the coefficient of non-linearity of the varistor at elevated temperature.