Development and Experimental Evaluation of Leakage Current Measurement Sensor for Electrical Power Apparatus

Abstract Leakage current measurement plays an important role in determining the healthiness of high voltage insulation of a power apparatus. High voltage (HV) insulation degrades due to electrical, thermal and mechanical ageing and their cumulative effects, and thus the leakage current of the insulation increase over a period of time. The accurate and real time measurement of leakage current enables the utilities to on-line access the healthiness of the insulation. This paper describes about the design, development, calibration and testing of a novel non-contact type passive leakage current sensor which can be used for monitoring of various electrical devices based on the analysis of the leakage current captured by the sensor. The developed sensor has been successfully used for measurement of leakage current in oil-filled HV bushings as well as in gas insulated surge arresters. The sensitivity of the developed sensor as per its design can be in the order of few milli amperes in case of bushing and in the order few micro amperes for surge arrester monitoring. The paper also reported a novel design of bushing adapter-sensor assembly for on-line measuring the leakage current in HV bushings without using the conventional capacitive or resistive tapping based measurements. Further, results covering experimental leakage current measurement on a 420 kV bushing using the developed adapter sensor assembly have also been presented. To establish capabilities of the developed sensor with optimized design parameters, laboratory measurements of leakage current on 420 kV and 145 kV GIS surge arresters have also been carried out and reported in the paper. Third harmonic content of surge arrester leakage current has also been estimated in-line with IEC requirement to assess the healthiness of the surge arrester. Finally, suitability of the developed sensor for leakage current measurement of above power apparatus equipment has also been analyzed and discussed.