Charging Mechanisms of a Conducting Particle on Dielectric Coated Electrode in SF₆ Gas

Abstract

The authors studied the charging mechanisms of a particle on dielectric coated electrode at AC and DC electric fields. The partial discharges at the small gap between the particle and the dielectric were observed by a sensitive optical measurement system, and lift-off stresses were measured. The stresses of partial discharge initiation and lift-off increase with the gas pressure at AC stress. This suggested that the particle on the dielectric coated electrode was charged by the partial discharges. The lift-off stress had the minimum at the dielectric film thickness of around 80-90μm. This property was understood by combining the stress of partial discharge initiation and the net charge for the lift-off calculated under measured lift-off stress. In the short term test at DC stress, the stress of lift-off increases with the gas pressure as well as at AC stress. From the short term test and the long term one at DC voltage application, it is concluded that the partial discharge at the small gap between the particle and the dielectric is the mechanism charging the particle, though the light emission generated by the partial discharge was not detected by the optical measurement.