UHF partial discharge monitoring of 400 kV GIS at Castle Peak substation

China Light and Power Co. Ltd., have embarked upon a trial installation of partial discharge (PD) measurement in gas insulated switchgear (GIS) using an ultra high frequency (UHF) detection technique. The system has been evaluated at a major 400 kV GIS installation at the Castle Peak power station site. The use of this technique is being considered by the Transmission Department as part of a diagnostic testing programme for predictive maintenance of GIS. The authors describe the findings of two site surveys conducted six months apart. The PD measurements were achieved by use of an external UHF coupler located at the viewing ports of the GIS disconnector enclosures. Both sets of results have displayed a high degree of consistency and have indicated the location of 16 discharge sources within the GIS. It is concluded that this technique demonstrates further potential and, in conjunction with a number of internally fitted couplers, could provide an effective PD monitoring system for this and other locations