Abstract
Effect of a thin insulation film on breakdown phenomena in liquid nitrogen in the presence of thermally induced bubble is investigated with a cylinder-to-plane electrode. Bubbles were produced by a heater mounted in the cylinder which is partially covered with an insulation film. The results show that the effect of film on the breakdown voltage is little till a pore is formed on the film by a previous breakdown, but it becomes very severe after the pore formation. The reduction rate in breakdown voltage after the pore formation depends on the gap length and heater power. The minimum breakdown voltage reaches down to the gaseous one at normal boiling temperature. Breakdown mechanism is discussed on the basis of bubble observation and numerical calculation of suspended-bubble motion.
