Investigation of flashover characteristics under nanosecond pulse in vacuum

Dependence of Flashover Voltage on cone angle of conical frustum, diameter of cylindrical insulator, gas pressure and electrode material has been experimented in high vacuum (10-5-10-1 Pa) under 10/30-nanosecond pulse power. It has been shown experimentally that cone angle has much effect on flashover voltage, and flashover voltage of 45° conical frustum is the highest. Surface flashover voltage of ± 45° conical frustum under short pulse waveform is much higher than that of cylindrical insulators, and the amplitude of flashover voltage for dc and power frequency ac voltages is lower. Electric field in CTJ (cathode triple junction) of 45° conical frustum is lowest; flash-over voltages decrease with the diameter of the insulator, and the reason for reduction is because the increasing length of the triple junction provides more relatively weak points for the initiation of surface flashover; flashover voltage is independent of the gas pressure under high vacuum, and flashover is in fact a type of gaseous discharge in a high-pressure phenomenon immediately above the insulator surface. There is no appreciable difference in flashover voltages for different electrode materials. According to experimental data and mechanism analysis, several suggestions are recommended regarding how to design an insulator used in vacuum circumstance.