Correlations between electrical and acoustic detection of partial discharge in liquids and implications for continuous data recording

Simultaneous measurements were made of electrical and acoustic signals from partial discharges (PD) produced by applying an alternating voltage at a frequency of 70 Hz to a point-plane electrode gap immersed in transformer oil. Both internally and externally mounted acoustic sensors were tested, and in all cases the intensity of the acoustic PD signal was found, on average, to increase with the amplitude of the electrical PD signal. The correlation between acoustic and electrical PD signals was found to be consistent with results reported from previous investigations. It is shown here that, because of this strong correlation, it is possible to extract statistical information from continuously recorded acoustic PD data, such as pulse phase (time) and amplitude distributions that are in agreement with those obtained from the electrical data. It is demonstrated that by having continuous records of all PD events that occur during a test, it is possible to uncover new statistical information that is useful in attempts to understand the physical basis for the phenomenon.