Characteristics of electrical charging on smooth and rough surfaces of glass plates under vacuum

To investigate the electric-charging characteristics of an insulator under vacuum, a system for measuring the potential distribution on the surface of an insulator under vacuum was developed and used to measure potential distributions on smooth and rough surfaces of several glass plates. The measured potential distributions after surface discharges indicate that compared to discharges on the rough surface, the discharges on the smooth surface tend to occur at lower positive potential. On the other hand, during micro discharge caused by partial discharge of the electrode, in the potential distributions of both the smooth and rough surfaces, a negative peak near the negative HV electrode and a positive peak near the GND electrode were observed. Moreover, the positive electric field on the rough surface is lower than that on the smooth surface during micro discharge. These potential distributions are supposed to be caused by scattering and attachment of electrons drifting on the surface. Sandblasting was applied for roughening the insulators, and it is considered to be suitable for mass production of the vacuum-insulated DC high-voltage systems because it is low cost and easy to perform.