The influence of external magnetic fields on the partial discharge characteristics of voids

This paper presents an initial investigation on the effect of an external magnetic field on partial discharge (PD) characteristics of voids in solid dielectric media, with a particular focus on statistics parameters derived from the classic phased-resolved patterns. Although it has long been known that high magnetic fields are present in equipment such as power transformers where PD may occur, only a few investigations have been made on the effect of the magnetic field on the discharge characteristics, and in these cases only the point-plane configuration has been considered. In the present study, magnetic fields of up to 128 mT were applied across several voids of known dimensions. Electric field stressing was simultaneously applied to produce PD, and the phase-resolved characteristics were recorded both before and after the application of the magnetic field. While variations in statistics parameters were observed, these were no greater than the observed variations over time in the absence of a magnetic field due to other physical phenomena in the voids. It is proposed that due to the encapsulated nature of the void and variability in PD characteristics, the effect of external magnetic fields up to the stated magnitude do not significantly alter statistical PD parameters. Although this goes some way toward validating the application of such parameters acquired under laboratory conditions to field-based measurements in equipment with high ambient magnetic fields, additional experimentation is needed to confirm this for higher field magnitudes.