An efficient method to characterise the performance of metal oxide varistors

Zinc oxide (ZnO) varistors have been used in protection systems and especially gapless surge arresters for nearly 3 decades. Their superior performance has been proved; but some aspects of their ageing mechanisms and their full capabilities have not yet been fully understood. The homogeneity of ZnO varistors granular structure has been found to be very important and is directly related to their energy absorption capabilities. This paper presents a newly developed varistor bulk current distribution mapping technique that is able to characterise the homogeneity of ZnO varistor devices. Assessment of the varistor´s homogeneity is believed to be very important in both the development stages of new varistor materials as a quality control tool and also to help understand some aspects of their ageing mechanisms