Measurement of spatio-temporal behavior of surface electrical potential in a dielectric creeping discharge using Pockels effect*

 A creeping discharge on dielectric surface has a great influence on the insulation design of power equipment and electronic devices, while it can be utilized in a wide variety of engineering applications, such as surface modification of materials, stall recovery of stable wings, and so on. As a streamer extends along the dielectric surface in a creeping discharge, charge-up phenomena on the surface are observed after the discharge, affecting the following breakdown on the surface. We have observed spatio-temporal behavior of electric potential on a dielectric surface using the Pockels effect, when a creepage discharge occurs at atmospheric pressure and a streamer propagates on the surface.

A high-voltage of several kV with sinusoidal frequency of 5kHz was applied on two electrodes (Cu tapes) set on a BGO (Bismuth germanate (Bi4Ge3O12) ) crystal. Electric potential was derived from phase shift of visible light passing through the crystal. Charge-up phenomena on the surface during sinusoidal phase of applied voltage were observed. Residual charges tend to remain at center region and positive residual charges remain more than negative charges. Correlation coefficients between each voltage phase were evaluated in order to clarify the charge up effect.