Abstract: In order to study the time-dependent characteristics of ZnO varistor’s microscopic capacitance after AC and DC degradation, a theoretical analysis is made on the parameters which influence the microscopic capacitance of ZnO varistor based on the block model. By applying the AC and DC degradation test on the samples of ZnO varistors with different experimental time, it is found that the macroscopic capacitance tends to decrease firstly and then increase after AC and DC degradation. When the AC and DC degradation time is relatively short, the microscopic capacitance reduces a little compared to the initial value. When the AC and DC degradation time is long enough, the microscopic capacitance substantially increases compared to the initial value. Based on the investigating results, it can be concluded that the time-dependent characteristics of microscopic capacitance are resulted from the releasing process of electron captured by interface state and the thermal failure process of grain boundary layer, which has a certain reference value for studying the degradation properties of ZnO varistor.

Key words: ZnO varistor, Schottky barrier, AC and DC degradation, macroscopic capacitance, block model