The role of electrostatic and hydrodynamic forces in the electrical breakdown of liquid dielectrics

Optical studies of prebreakdown events in insulating liquids make it possible to identify several stages in the breakdown of negative point-plane gaps, starting with the creation of a rapidly expanding vapor cavity adjacent to the point electrode. As it expands the surface of this cavity becomes unstable and the growth of an electrohydrodynamic instability is observed; the runaway growth of this instability leads to streamers that bridge the gap and cause the actual breakdown. By combining simple electrostatic and hydrodynamic concepts one can derive equations for cavity growth, instability growth rate, and streamer velocity that are in reasonable agreement with experiment.<>