Effects of chemical impurities on prebreakdown events in toluene

Effects of chemical impurities on the breakdown process in toluene have been investigated under non-uniform field conditions using a high-speed image converter camera. The resistivity of the four samples investigated ranged from 109 to 1013 Ω cm. It was noted that when the cathode was a point, streamer growth rate increased slightly with decreasing resistivity. When the needle was an anode, streamer growth rate was not measurably affected by changes in resistivity or applied voltage, requiring 1.6 ± 0.3 μs to cross the 3 mm gap. Independent of the polarity of the needle, the last step in the traverse leading to breakdown of the gap occurred at speeds greater than 1 × 106 cm/s. In purified toluene, more than 200 kV could be applied to a 3 mm gap without breakdown. With the needle as a cathode, impurities facilitated the generation of secondary streamers which appeared to grow from the primary bush-like streamers. With decreasing resistivity, the branching of these streamers seemed to increase.