Observations of echo phenomena acquired from partial discharge measurements in voids

Abstract

In this paper, a new observation relating to partial discharge is presented, called partial discharge echo. Partial discharge echo refers to the occurrence of partial discharges in the part of the chopped sequence where no voltage is applied, following exposure of the specimen to a sinusoidal voltage above the partial discharge inception level. The phenomena relates to several aspects of the chopped partial discharge sequence, namely a charge accumulation in the void and the buildup of an internal field, the remnant field which, remains after the external voltage has been removed, space charge, as well as the processes of charge decay related to surface material conductivity. The measurements were performed on specimens with an embedded void in cross-linked polyethylene. In order to capture the echo signal, a modified phase-resolved partial discharge acquisition setup was used. The discharge echo pulses may allow the void to be analyzed in greater detail, revealing specific mechanisms, for example time lag, surface charge decay and relation to void conductivity. Thus partial discharge echo opens the possibility for various investigations of discharge dynamics and dielectric degradation, especially providing detailed insight into high voltage insulating systems.