Dielectric Characteristics of Gas Insulated Bushings in Air Under Dry and Wet Conditions

Dielectric characteristics of an EHV gas insulated bushing to be used for SF6 gas insulated switchgears are reported. From observation of the lightning impulse flashover under dry conditions with an image converter camera, the flashover process of the bushing in air is clarified. It was found that the electric field strength of the porcelain surface on the lower part of the bushing had a large influence on insulation performance. The tilt angle of the bushing was changed as a result of studying the switching impulse dielectric characteristics of the bushing under wet conditions; and the water stream on the exterior surface of the bushing was seen to have a large influence. It was demonstrated that dividing the water flow along the porcelain surface made an improvement in insulation performance.