Anomalous Positive Point Prebreakdown Behavior in Dielectric Liquids

An experimental study was performed to determine the nature of events which lead to electrical breakdown in the normal alkanes from n-pentane to n-decane, and toluene. Disturbances prior to breakdown were rendered visibl by means of a shadowgraph optical system. Both electronically framed and high resolution single exposure photographs were taken during the prebreakdown period. Two distinct types of prebreakdown disturbance were observed whe using a point anode. In addition to the normally expected supersonic streamer, a new subsonic bush-like structure was recorded. Factors affecting the generation of the subsonic event were investigated, and are considered in terms of a gas phase process.