Spark Discharges in Low Pressure Sulphur Hexafluoride

Abstract

The present thesis describes the various phases of development in low pressure (~ 1 Torr) sulphur hexafluoride (SF₆) sparks formed in long gaps (4 - 100 cm) and at overvoltages greater than 100%. ... Chapter 3 deals with the experimental results relating to certain aspects of the prebreakdown, breakdown and postbreakdown regimes in the low pressure SF₆ spark, with most of the emphasis placed on postbreakdown development. The various phases and transitions in the growth of the spark are catalogued and discussed in the light of experimental observations. The results indicate the existence of two distinct abnormal glow phases. The mechanism of the transition from the first to the second glow phase is accounted for in terms of molecular dissociation. The transition to the arc phase is observed to be encouraged by the presence of insulating surfaces surrounding the cathode. This transition, which has been accounted for in terms of a field-emission mechanism, can occur from either of the two glow phases. Following a description of the various phases and observed phenomena, a summary and general conclusion are presented.