Analysis On The Varieties Of ZnO Varistor’s Characteristics During The Impulse Of 8/20μs Current

Under the impulse of large current, the internal structure of ZnO varistor inevitably exist the degradation phenomena, which may cause potential safety hazard to the normal operation of electric system. Based on the above reasons, it is necessary to research on the varieties of ZnO varistor under the impulse of large current. This paper mainly focuses on the varieties of ZnO varistor during the impulse of 8/20μs current and analyses the changes of ZnO varistor’s properties such as macroscopic capacitance, residual voltage ratio and AC aging characteristic, by taking the impulse experiments, we can draw conclusions as follows:The C-t curve of ZnO varistor takes on a decreasing trend after receiving the impulsive current, and then takes on a increasing trend. By analyzing the related parameters of Block-Model which influence the value of ZnO varistor’s macroscopic capacitance, we can realize the changes of macroscopic capacitance are resulted from the recombination of deep donor-like defects and the releasing process of electrons captured by interface states during the middle electric field. Based on these conclusions, we can put forward the changes of macroscopic capacitance can be regarded as the basis of the degradation state. The impulsive experiment proves that on the experiment which under the impact of In value, the capacitance will first take on the downward trend and then take on a upward trend, the product of U1mA and capacitance is almost a constant at the beginning of degradation,then the product of U1mA and capacitance drops sharply, on the experiment under the impact of Imax value, the capacitance and the product of U1mA and capacitance drop constantly. In this case, we can describe the variation characteristics of the grain boundary based on the conclusions from experiments, and consider it is better to estimate the degradation degree by combing the macroscopic capacitance.It was found that the residual voltage ratio will first decrease slowly, and then increase slowly and finally increase sharply during the impulsive experiment. Based on double Schottky barrier theory and thermal aging theory, the residual voltage ratio was determined by the state of grain boundaries; the sharply-increasing stage of residual voltage ratio was resulted from the destruction of grain boundaries. It was proposed that the change rate of residual voltage ratio can better estimate the degradation degree of ZnO varistor.Based on the theoretical analysis of ZnO varistor’s aging mechanism, It is found that impacted by the proper times of impulse current, the AC withstand ability of ZnO varistor is strengthened; During the process of AC aging, U1mA and U0.1mA slowly increased at first, then decreased slowly and sharply dropped in the end. Nonlinear coefficient decreased slowly at the beginning and then quickly decreased; according to the experimental results, we can further prove the correctness of degradation mechanisms of different process, which has a certain referential and value for the degradation diagnosis on ZnO varistor.