Properties of ZnO varistor blocks under multiple lightning impulse voltages

This paper presents the effect of multiple impulse voltages on the electrical and physical properties of a zinc oxide (ZnO) varistor. To investigate the dynamic characteristics of a ZnO varistor subjected to multiple impulse voltages, we designed and fabricated the multiple combination wave generator. The multiple combination wave generator can produce quintuple 1.2/50 μs impulse voltages of 100 kV and quintuple 8/20 μs impulse currents of 12 kA. Applying these voltages and currents, the electrical and physical properties of the ZnO varistor were evaluated. The multiple impulse failures of a ZnO varistor are mainly caused by the surface flashover. When multiple impulse voltages are injected, the charge enhancement near the joined edges of a ZnO varistor and metal electrodes plays a decisive role on the surface flashover or breakdown initiation and developments. Also, after the injection of the quintuple 8/20 μs impulse currents of 10 kA, the residual voltage and quiescent current of the ZnO varistor were changed markedly.