Criteria for Spark Breakdown in Sulfur Hexafluoride

Possible mechanisms of spark breakdown in SF6 and other electronegative gases are discussed, and quantitative criteria are derived for the Townsend type and the streamer type of breakdown in nonuniform fields. The Townsend criterion is of considerable physical interest but difficult to apply to engineering problems, whereas the semi-empirical streamer criterion, which holds for impulse breakdown, can be applied to any gap geometry of known field distribution.