Partial discharge echo obtained by chopped sequence

This paper describes a new and intriguing observation relating to partial discharges specifically those discharges which occur despite the absence of an applied voltage within chopped sequence. The discharge pulses, which are referred to as Partial Discharge Echoes, appeared in intervals where no voltage was being applied, immediately after the specimen had been exposed to a sinusoidal voltage above partial discharge inception level. The measurements were performed on specimens with an embedded void in insulating paper or cross-linked polyethylene. In order to capture the echo signal, a modified phase-resolved partial discharge acquisition setup was used. The discharge mechanism around the transition point from sinusoidal to voltageless, echo intensity and impact of void material type were analyzed. The discharge echo pulses may allow the void to be analyzed in greater detail, revealing specific details of some of the mechanisms, for example time lag, surface charge decay and relation to void conductivity.