Time-resolved measurements of surface flashover of conical insulators

The voltage at which an insulator in vacuum flashes over depends on the angle between the insulator-vacuum interface and the electric field.1,3 In the work reported here, fast high-voltage pulses (3 ns risetime) and nanosecond time resolution permit measurement of the time delay between voltage application and breakdown. Measurements indicate that much of the angular variation in breakdown voltage observed under fast-pulsed conditions is associated with a seconary electron emission avalanche1 5 at the insulator surface preceding breakdown. The voltage dependence of the time delay provides insight into the transition from electron avalanche to low-impedance discharge. Furthermore, there is evidence that a different mechanism may lead to surface flashover within a restricted range of electric field angles.