Performance analysis of modified shifted current method for surge arrester condition monitoring

The gapless zinc oxide surge arresters enable the utility personnel to measure the leakage current due to its gapless physical configuration. An arrester leakage current which comprises of capacitive and resistive components is such an important parameter to be analyzed because its third harmonic resistive component is known to be directly related to the ageing or the degradation of the zinc oxide arrester itself. Various methods can be applied to monitor the condition of the surge arresters both for in-field as well as inside a laboratory. The resistive component extraction method called the Modified Shifted Current Method (MSCM) is utilised in this work. A portable device consisting of a tablet computer is able to measure and store the leakage current data and therefore can be used for an in-situ arrester condition assessment. This paper describes the performance of the portable device when measurements of the arrester leakage current were conducted at the 132-kV transmission substations. The leakage current data were analyzed and summarized to indicate its performance in terms of the accuracy of assessments made on the arrester conditions in actual substation environment.