Discharge Randomness and Attraction Process of Epoxy Surface on Discharge Channel in SF6 Gas Under Uniform Electric Field

Abstract

It is generally believed that due to the electric field distortion effect and the photoemission process of the solid surface, the discharge channel near the solid surface trends to develop along the surface than that in bulk gas. One way to improve insulation performance is to avoid the solid surface from participating in the gas discharge process. However, the mechanism of the solid surface’s effect on the gas discharge process is still unclear. In this paper, we recorded high-speed framing pictures of the discharge process in SF6 gas near the epoxy surface under lightning impulse voltage in the uniform electric field. The arc pictures show that the attraction effect of the solid surface to the discharge channel is related to the surface shape, gas gap height, and distance from the discharge channel to the solid surface. Besides, discharge randomness also plays a role, which is more obvious in the cylinder insulator than in the conical insulator, for the surface with conical shape could easily attract and arrest the discharge channel to its surface. According to the pictures of discharge process near the cylinder surface, we found that the photoemission process occurs in the streamer stage but has little effect on the attraction effect. The leader initiates after the streamer bridges the gas gap, and its random stepped walk could induce the attraction effect from the solid surface: only when the random stepped leader deflects close to the solid surface, the discharge channel could be further attracted to the solid surface by the electrostatic force, especially its normal component. The result indicates that there are three points to prevent the solid surface from participating in the gas discharge process and further improve insulation performance: choose a cylinder shape (avoid a conical shape), keep the surface away from the high electric field area where discharge may start, and reduce the normal component of the surface electric field.