Optical Study of Conduction and Breakdown in Dielectric Liquids

Abstract

On the optical studies of electrical conduction and breakdown in dielectric liquids, recent works which have been studied in Japan are briefly reviewed first. Next, the results of study in our laboratory on the measurement of ion mobility and on the breakdown process in liquids are presented. When an electrode system such as razorblade emitter-grid-collector is used for the measurement of ion mobility by the time of flight method, the field uniformity between grid-collector is calculated, and the space charge effect related to the current density is investigated. Through these researches suitable condition for ion mobility measurement are revealed. On the breakdown process, the schlieren method and high-speed photography are used under a pulse voltage applied to a needle-plane gap. Various aspects of the breakdown process from streamer initiation to main stroke, the polarity effect of streamer propagation, the relation between the mean velocity of positive streamer Vm and molecular structure of liquid, the relation between vm and pre-breakdown current, Vm of mixed liquid etc. are described.