Identification of simultaneously active partial discharge sources using combined radio frequency and IEC60270 measurement

Using a newly developed measurement system, partial discharge (PD) activity has been recorded simultaneously on a pulse-by-pulse basis in terms of radiated radio frequency (RF) energy and the conducted apparent charge measured according to the IEC60270 standard. Two epoxy resin insulation samples containing voids have been activated separately and in parallel and the resulting PD was measured using the combined system. It has been shown that the combined measurement system has the ability to distinguish between discharges occurring simultaneously in each of the respective samples. This is evident in the appearance of separate clusters when the energy of the radio frequency discharge signal is plotted against the apparent charge for a large number of pulses. The identity of the defect producing each cluster has been confirmed by modelling the complete response of a gas-insulated-switchgear chamber to simulated Gaussian current pulses of known charge. The combined technique has also shown potential to distinguish between additional simultaneously active defects, including free metallic particles in oil. The combination of the two measurement systems may enable the classification of PD activity with a greater degree of confidence than conventional phase-resolved measurements allow when more than one defect is present.