Low voltage disk varistors under non-standard high current derivative impulse environment

Abstract

In this study, the behavior of low voltage disk varistors was analyzed under oscillatory type non-standard high current derivative impulses. The experiment was performed using 20mm disk varistors with different nominal operating voltages of 14, 30, 40, 75, 150, 250, and 275V. Non-standard current impulses were generated using a Van De Graaff generator. The current impulse is in the shape of double exponential oscillatory type wave which has the oscillation frequency of 14.53MHz. The rise time of the impulse was found to be 8ns with the maximum peak current rate-of-rise of 2.41×1011A/s. According to the results, under very fast non-standard current derivative impulse environment, clamping voltage could be depend on both nominal voltage of varistors and the peak current rate-of-rise of the injected impulse. Interestingly, the clamping voltages under non-standard high current derivative impulse environment for all the tested varistors were below the order of values reported for 8/20μs standard current impulses. It is believed that the varistor response is mainly governed by the lead's inductance whereas the influence of the varistor nonlinear resistance becomes negligible. It was found that the maximum impulse impedance values of the varistors are caused due to the increasing of its nominal voltage. Calculated current integrals were lying between 80 and 94A2s whereas the maximum peak current values were lying in the range of 2070–2496A. Another important feature observed in this study was the DC offset voltage appears between terminals of varistor immediately after it is triggered due to its first oscillatory pulse of the current impulse.