Conduction and breakdown initiation in dielectric liquids

In this paper we present the main electrical conduction phenomena which can occur, from low up to very high electric field, in dielectric liquids. Such phenomena are greatly dependent on the applied electric field strength. We analyze the influence of the liquid permittivity and of the applied electric field on the concentration of free charge carriers, as well as in the bulk of the liquid than at the metal/liquid interface. The possible correlation between high field conduction phenomena and breakdown initiation is then discussed. The liquid breakdown is generally the consequence of the initiation of a localized discharge (called “streamers”) which requires a very high electric field (∼500MV/m) followed by its propagation into the liquid under a much lower electric field (∼1MV/m). Some possible mechanisms leading to this discharge initiation and then to liquid breakdown will be presented and discussed.