Surface flashover of ceramic insulators in vacuum at room and liquid nitrogen temperatures

DC and impulse surface flashover of ceramic insulators in vacuum is studied at room and liquid nitrogen temperatures. By cooling only one of the electrodes at a time it observed that anode cooling had little influence on the flashover voltage, while cooling the cathode to liquid nitrogen temperature increases the flashover voltage by 20 per cent under DC and by 50 per cent under lightning impulse voltages. Ultra high speed photographic records show that measurable light first appears at the cathode and progresses towards the anode, under impulse voltages at a speed of approximately 1.5×10⁶ m/s, and at 4×10⁷ m/s under DC voltages. Absorbed gases on solid surfaces are considered important in discharge development.