Effect of Ambient Temperature on Leakage Current of Gapless Metal Oxide Surge Arrester

Zinc oxide (ZnO) gapless surge arresters are used for lightning and overvoltage protection in electrical power system. The leakage current monitoring is one of the well known method for the ZnO surge arrester ageing level determination. However, the ZnO leakage current is known to be dependent on the ambient temperature. This paper aims to study the effects of temperature variation due to ambient conditions on the leakage current of ZnO surge arrester. The effect of a significant increment of leakage current with an increase in temperature may result in a wrong assesment of the ageing level of the arrester. The leakage current of three 120kV rated polymeric housed ZnO surge arresters were measured in a custom made thermally insulated enclosures at varying temperatures. Up to 20% increase in the leakage current was observed with a 20°C increment above the ambient temperature. For a typical variation of ambient temperature in Malaysia in the range of between 30°C and 40°C, the corresponding changes in the leakage current can be up to 11%. The temperature does significantly affect the leakage current measurements used for monitoring of zinc oxide surge arresters. This significant change in the leakage current due to ambient temperature variation can affect the decision in assessing the condition of surge arresters during routine monitoring.