Profile effect on surface flashover in a uniform field

Flashover results on insulator specimens with different profiles in a uniform electric field in air are presented. Under direct voltages, positive streamers, propagating along cylindrical insulators, inserted perpendicularly between two parallel plane electrodes, result in breakdown. Breakdown in air alone is studied as a reference. Breakdown fields and times to breakdown are measured as influenced by the pulse voltage amplitude used for the streamer initiation, and by the insulator profile. A higher electric field is required for breakdown along an insulating surface rather than in air. It is shown that a strong relation between the discharge propagation and breakdown exists; the insulator profile exerts similar influence on the breakdown field as on the propagation field.