Effects of Electromagnetic Field on Partial Discharge Behavior in BOPP Film Capacitors

In this article, an experimental system is established to characterize the internal, surface, and corona partial discharge (PD) properties of polypropylene films under a magnetic field. With the increase of the magnetic flux density, the PD inception voltage in various defects is reduced by 5%–12%. At the same time, the number of discharges under the magnetic field increases by 126%, 183%, and 61%, respectively. The magnetic field changes the charge-moving direction and reshapes the charge distribution through the Lorentz force. The influence of the magnetic field on internal discharge in the negative half cycle is more significant, by exciting electrons and distorting the electric field. The proportion of PD in the negative half cycles increases from 58.4% to 71.8%. The change of discharge characteristics on the surface is mainly reflected in the broadening of the discharge phase, which is due to the recombination of bipolar charges separated by the magnetic field and accumulated on the surface of the sample. The corona discharge ratio in the positive half voltage cycles increases from 9.50% to 22.1%, although it is still far less than that in the negative half voltage cycles. The trajectory of electrons in the air is changed by the magnetic field, which enhances the electric field near the high-voltage electrode in the positive half cycles.