Use of partial discharges measurements and video recordings to investigate the influence of relative humidity on zinc oxide subjected to high electric fields

Abstract

This study investigates the influence of humidity on the high voltage behaviour of zinc oxide porous pellets at room temperature, using the phase resolved partial discharge (PRPD) method. The experimental configuration corresponds to the one that would be used for flash sintering cylindrical ZnO pellets at low temperatures in possibly scalable conditions: planar Pt electrodes without Pt paste. The study explores the incubation period by increasing the 50 Hz AC electric field up to 8 kV cm−1 (applied by steps or with a continuous ramp) in an air atmosphere with varying relative humidity (RH). Experiments were repeated on several samples and showed that the maximum amplitude of PDs decreased while their number increased as the RH increased. With the support of video recording of the experiments, different characteristics in the PD pattern evolution with increasing AC voltage could be attributed to various locations between the electrodes, at the sample surface, or at the interface with the electrodes. By examining the PRPDs, it was possible to identify two distinct types of PDs having different thresholds of inception: one type corresponds to PDs occurring mostly at the triple junction ‘ZnO-platinum-air’ or in the ZnO-electrodes gap and depends strongly on the RH level and; the other type corresponds to electric arcs between the electrodes, with an inception threshold much less affected by the RH level.