PREBREAKDOWN PHENOMENA IN DIELECTRIC LIQUIDS

The aim of this paper is to make a synthesis of a number of characteristic features of prebreakdown phenomena in liquids, e.g. those events which precede are development. The subject is restricted to short term processes in the bulk, more specifically of hydrocarbons. First, the basic physical properties involved in the prebreakdown mechanisms will be considered, with special emphasis on the influence of pressure and temperature on the physical and electronic properties of liquids and their vapor. Following this, the advantages of using a point-plane electrode geometry to study separately cathodic and anodic prebreakdown stages will be demonstrated. To begin with, there is injection of carriers which consequently produces avalanches in the liquid followed by bubble generation. These mechanisms are now well characterized. Eventually, discharge channels are developed, streamers or leaders. The initiation and the propagation of these channels depend on many experimental conditions which are discussed. Characterization and understanding of these phenomena are in progress. Finally, prebreakdown phenomena in uniform fields are considered, either at short (mu m) gaps or at large gaps, in the presence of large protrusions or free moving particles.