Field experience on surge arrester condition monitoring - Modified Shifted Current Method

The gapless surge arresters enable the utility personnel to measure the leakage current due to its gapless physical configuration. 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 metal-oxide arrester itself. Various methods nowadays can be applied to monitor the condition of the surge arresters both for on-line (on-site) and off-line (off-site). A new resistive component extraction method called the Modified Shifted Current Method (MSCM) is described in this work. This method has been applied to a newly developed portable device for easy on-site gapless surge arrester condition monitoring. This device consists of a tablet computer and is able to measure and store the leakage current data and is reliable for in-situ arrester condition assessment. Being newly developed and having tested inside the laboratory, this portable device was tested in the actual on-site application where the effects of various factors and interferences were studied. This paper describes the field experience of the portable device when measurement of the arrester leakage current were conducted at the 132-kV and above transmission substations. The leakage current data were analyzed and summarized to indicate its performance in terms of accuracy of assessment and in-situ decision made on the arrester conditions in actual substation environment.