Effect Mechanism of Surface Roughness of Solid Dielectrics to Surface Discharge Voltage in Liquid Nitrogen Under Lightning Impulse

The surface discharge of solid dielectric in liquid nitrogen has become one of the key problems in the development of high-temperature superconducting power devices. It is necessary to study the mechanism of surface discharge of the solid dielectric in liquid nitrogen. This article chose polytetrafluoroethylene and DW-3 epoxy resin as specimens, tested the surface discharge voltages of two kinds of specimens with different surface roughness under lightening impulse voltages in liquid nitrogen, and discussed the effect mechanism. The experimental results showed that the surface discharge voltage and discharge time of both materials in liquid nitrogen increased as the surface roughness increasing under lightning impulses. The surface roughness affects the surface discharge voltage of the solid dielectric in liquid nitrogen under lightning impulse, mainly in the charge left on the grinding surfaces of solid dielectrics, the heights of projections, and the creepage distance on the dielectric surfaces. The main discharge process is in the gasification path, and the effect of solid dielectric on surface discharge in liquid nitrogen is smaller. These reasons make the surface discharge in the liquid nitrogen less affected by the surface roughness. The results further explore the characteristics of surface discharge in liquid nitrogen and could provide methodological guidance to improve the surface discharge voltages in liquid nitrogen.