Impulse flashover in liquid nitrogen along a glass tube with a gas layer inside

Abstract

In atmospheric air, impulse flashover voltage along the outer surface of a layered dielectric composition, composed of two coaxial hard glass cylinders with a gas layer in between, is known to have a V-shaped curve as a function of the pressure of the gas layer. The authors examine whether such a phenomenon also occurs in liquid nitrogen. It was found that impulse flashover voltage in liquid nitrogen along the outer surface of the glass tube, inside which a gas layer exists, also shows a V-shaped pressure dependence, which is similar to the dependence observed in the case of atmospheric air. In normal hexane at room temperature, however, such as V-shaped pressure dependence was not observed. It is suggested, therefore, that gas bubbles vaporized in non-pressurized liquid nitrogen play an important role in the flashover mechanism. This finding is not only interesting from the viewpoint of discharge physics, but is also important in designing bushings or feedthroughs for electrical insulation at cryogenic temperatures. >