Insulation properties of highly pressurized dry air-effects of anodic oxide coating and surface roughness of electrodes on breakdown voltage

Dry air has been introduced to gas-insulated switchgears as an environmentally friendly insulation medium for SF 6 gas. Since its insulation strength is about onethird of SF 6 gas, to grasp the insulation properties of highly pressurized dry air is necessary to apply dry air insulation to further high voltage equipments. In this paper, to consider smaller products and higher voltage ratings, insulation properties in highly pressurized dry air was investigated. Especially, pressure dependence, surface roughness dependence and the effect of surface processes were investigated.