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Reference: ISH2015_36

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A novel technique for measuring HVdc insulator leakage current using magnetic field sensors



Leakage current monitoring for high voltage transmission line insulators is of interest as it may be a key indicator of potential performance issues. High voltage direct current (HVdc) lines are more difficult to monitor when compared to alternating current lines as the conventional current transformers cannot be used to measure dc current. Presently, there is no commercially available, clamp-on type, non-intrusive devices for HVdc line insulator leakage current measurements. The South African power utility, Eskom, is currently investigating the development of such a hand-held sensor for two important applications. First, for continuous real time monitoring of HVdc line insulators and second, for use by live line workers to determine if it is safe to work on energised insulators. In this paper, methods of measuring dc leakage current are investigated. Since magnetic fields associated with leakage currents are weak, magnetometers were investigated as a current sensing technology. Proof of concept laboratory tests as well as fog chamber tests were conducted for several different sensors and the results are presented here. These tests involved injecting a known dc current into a wire and using different sensors to detect the magnitude thereof. Fog chamber tests involved creating leakage currents across energised and polluted glass and composite insulators under high humidity ambient conditions. Two commercial-off-the-shelf sensors were used in this study, namely a fluxgate magnetometer and a dc leakage current sensor. Initial results show that these sensors can measure leakage current non-intrusively, hence this approach will be adopted for measuring leakage currents on in-service HVdc insulators.

File Size: 351,4 KB

Year: 2015

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