Prebreakdown processes in electrically stressed insulating liquids

Abstract

It has previously been reported that a spray originates from high-voltage point electrodes in n-hexane. This paper is concerned with more detailed investigation of that spray. Although it is more readily observed if the point electrode is negative, it can also be seen when the point is positive provided that the gap length is adequate. The distribution of spray in the gap of a point-plane system is approximately conical. The apex of the cone is about 60° for a negative point and 120° for a positive point. The spray appears to consist of bubbles which cross the gap with a velocity of the order of metres per second, and which have grown to become about 15 μm in diameter by the time they reach the plane electrode. Their size at the point electrode is not directly measurable but has been found to be an order of magnitude less by light-scattering measurements. The onset of the spray coincides with the appearance of corona at the tip of the point electrode, and the spray onset voltage is a function of the radius of the electrode tip. An account is given of some of the complex processes which seem to govern breakdown processes in insulating liquids.