Pre-breakdown mechanisms in dielectric liquids and predicting models

This paper presents a synthetic review of the state of knowledge relative to the pre-breakdown phenomena in dielectric liquids and especially the initiation and propagation of streamer/discharge and their characteristic parameters. The main influencing parameters namely the structure, stopping length, velocity and propagation modes of streamers, current, charge and associated emitted light are developed. These parameters include especially the chemical composition of the liquid (pure or containing specific additives); the applied voltage; the electrode arrangement; the temperature and the hydrostatic pressure. The mechanisms involving in the inception and propagation of streamers are discussed. Recent models enabling to predict the type of streamers that can be initiated and their characteristics when propagating within liquid, are also presented and discussed. It is shown through the experiments and modeling that the pre-breakdown phenomena in dielectric liquids are governed by both electronic and gaseous mechanisms even if one of them is dominant in one case and the second in another.