Changes in varistors properties after radial field test

ZnO varistors are used in commercial surge arresters in high voltage application in the area of power engineering. Metal oxide arresters (MOA) operated in polluted areas may be subjected to an environmental stresses causing an internal partial discharges (PD), increased varistor temperature, increased leakage current, which may lead to “thermal run-a-way”. Internal PD, increased temperature and increased current may occur due to the uneven voltage distribution created by the surface leakage currents. It may be achieved when different voltage distribution between varistor column and porcelain housing becomes, especially when the stable dry zone occurs. The author, in this work, establishes uneven voltage distribution immersing arrester in tap water. This paper present changes in varistors properties after radial field test. It was shown, that changes in currentvoltage characteristic can be result from degradation of insulating layer covering the varistors as result of the strong partial discharges created between internal surface of the porcelain housing and attentive surface of the varistors column