High-speed photography of prebreakdown phenomena in dielectric liquids under highly non-uniform field conditions

The electrical breakdown process in dielectric liquids for a point-to-plane gap configuration has been studied, using an image converter camera in conjunction with an image intensifier and a schlieren system. It is shown that the positive streamer has a tendency to keep its propagation velocity constant across the gap. The constant streamer velocity in benzene and toluene is equal to that of the accompanying shock wave. Discrete transition from primary streamer to fast secondary is occasionally observed for positive polarity. The aspect of negative streamer propagation in carbon tetrachloride is similar to that of the positive one. The development of the actual breakdown channel has also been observed in carbon tetrachloride. The results are consistent with models of a breakdown mechanism based on a field ionization process for positive polarity and an Auger-like electron emission process for negative polarity.