NANOSECOND STREAK PHOTOGRAPHY OF DISCHARGES ON SPACER SURFACE IN GASES

Results of an investigation to clarify the process of surface flashove r in gases are reported. Two hemispherical capped rods of 12 mm diamet er, separated by a half-cylindrical spacer of 50 mm diameter, formed t he samples. The spacer materials were polytetrafluoroethylene, acrylic and nylon. High-speed streak photographs of impulse flashover indicat e that the presence of a spacer not only lowers the impulse breakdown voltage but also reduces the breakdown time. The discharge on spacers may be initiated anywhere between the electrodes and develops rapidly into a flashover in similar to 5 ns for an 18 mm gap.