The internal distribution unevenness of current and heat in zinc oxide varistor under high current impulse, resulting in an increase in internal stress. In this paper, an experimental platform was built to acqurie the critical energy density of the failure of the varistor under different waveforms. The experimental results indicate that the critical energy density of the 2 ms square impulse is significantly higher than that of the 4/10 μs impulse, which is about 1.76 times. There is a certain difference in the proportion of failure phenomena under different waveforms. Under the 2 ms square impulse, the varistor will have puncture phenomenon. Under the 4/10 μs impulse experiment, the varistor mainly has two failure phenomena: flashover and cracking. An experimental circuit of hysteresis loop was built to obtain the magnetic permeability of the zinc oxide varistor under different frequencies. The results indicate that the permeability of the zinc oxide varistor decreased from 267 to 52 with the frequency increases from 100 Hz to 10,000 Hz. The finite element simulation model was established to simulate the current characteristics of the varistor under different current waveforms. The simulation results show that the amplitude of the stress under the 4/10 μs impulse current is much larger than that under the 2ms square wave, which is about 4000 times when the energy density is closely.  The energy density under different impulse currents is quite different. The analysis shows that the internal stress of ZnO varistors is more significant under high frequency impulse current.

ZnO varistor; failure modes; current impulse; permeability; finite element simulation; stress