Phase-resolved and time-sequential partial discharge pulse measurements in a metal-void-insulator system using a personal computer

We have developed a partial discharge measurement and analysis system using a personal computer, which allows one to obtain reproduced partial discharge pulse data with the phase information in an applied alternating current voltage and the number of cycles. For the CIGRE method II electrode system using 0.1 mm thick polyethylene film, temporal changes of partial discharge characteristics were measured up to breakdown of the sample. The average inception phase theta inc was proposed as a new statistical partial discharge parameter, which was obtained by making use of the capability of the time-sequential partial discharge data acquisition of our system; theta inc is defined as the average of theta inc of the number of cycles in a measurement; theta inc is a phase at which the first partial discharge pulse occurs in the half cycle after the polarity reversal of the previous partial discharge pulses. The experimental results revealed that the partial discharge pulse occurrence phase distribution ( phi -q-n distribution) exhibited a good correlation with ageing time. It was suggested that theta inc is a candidate signal for diagnosis of insulation performance of the system from the initial to middle degradation stage. We also discuss the physics of the temporal change of the phi -q-n distribution and theta inc as the ageing process proceeded.