Studies of the creepage discharge on the surface of liquids

Aspects of propagation of the creepage discharge on the surface of liquids are investigated by a high-speed Schlieren method, when an impulse voltage is applied to a point-to-plane gap arranged at the interface between the liquids and air. Distilled water, rain water, electrolytic aqueous solutions, and insulating oil, liquids with very different conductivity, were selected as the sample liquids. In the same instant of taking high-speed time-resolved Schlieren photographs, prebreakdown currents were measured using a light-emitting diode system. Through these experiments, a polarity effect in the shape and the size of the density changes, features and mechanism of propagation of the density changes, and their mean propagation velocity are discussed in conjunction with current measurements.