The effect of thermal transient on the leakage current of metal oxide arresters

The operation of surge arresters depends on the insulating packaging of zinc- oxide (ZnO) utilized in arresters. The leakage current within the arrester increases due to the decay on the insulating property. The decaying of the insulating property will increase leakage current within the arrester. The over-voltage that is generated from surges is clamped by the nonlinear characteristics of the ZnO block and is neutralized to its regular level. In this paper, an experiment has been conducted to monitor the leakage current behaviour at different thermal and ac low voltage stresses. The metal oxide varistors (MOVs) were subjected to thermal degradation under ac field voltage stress. Measured results from the MOV samples exposed to the electrical field and thermal stresses are presented and the leakage current behaviour is analysed. During the time of measurement, it was observed that the leakage current is affected by the applied temperature and voltage. The results obtained illustrate that as soon as the reference temperature approaches higher temperature a high rise in leakage current is generated and self-healing phenomenon is clearly observed during the thermal transient.