Surface pollution of outdoor high-voltage insulators is an important cause of flashover. We have undertaken an experimental study of electrical breakdown at the edges of a sessile water droplet on a planar, polymeric, insulating surface when subject to AC stress, parallel to the insulator surface, up to 2MV/m. The static contact angle between droplet and surface was varied by controlling the physical properties of the droplet and by inclining the insulator plane from the horizontal. The partial discharge activity from the water droplet was investigated using a combination of high-speed video camera, operated at up to 3,000 frames per second, and an electrical partial discharge detection system. We have used this to examine the location of partial discharge at the edges of the water droplet.
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