Streamer propagation times along insulator surfaces in transformer oil

The electrical failure of practical oil insulated apparatus often develops as a surface flashover along the interface of a solid dielectric support and the oil. While there is substantial reported information about breakdown and streamer propagation in plain oil gaps, there is little comparable information about the surface flashover case. The studies reported here concern measured surface flashover characteristics and mechanisms of a point-to-plane gap with a solid dielectric surface perpendicular to the plane bridging the gap. A nanosecond risetime step voltage was applied, and the currents and time to breakdown were determined by an electro-optic coupling method.