Influence of Surface Roughness on Breakdown in Air Gaps at Atmospheric Pressure Under Lightning Impulse

In high voltage equipment, gases are often used as insulation material. Several parameters can influence the dielectric withstand voltage of gaseous insulation systems, such as the degree of inhomogeneity, gas pressure and type as well as surface roughness. This study focuses on the influence of surface roughness on the withstand voltage of atmospheric pressure air gaps under lightning impulse stresses. For this purpose, surface profiles of different rough metallic surfaces have been characterized using an optical surface scanner with a resolution of 3 nm. Based on the extracted features of the surface roughness, axial symmetric random surface profiles have been generated in a multi-physics simulation tool, electric field simulations performed, and streamer criterion applied to estimate the breakdown voltage. To verify the simulation results, lightning impulse breakdown voltage measurements have been carried out in simple configurations (sphere plate and rod plate) for four different degrees of surface roughness of the plate electrode. The experimental results confirm the observed trend in simulations, where the breakdown voltage is only to a limited extend reduced even for considerably rough surface profiles.