Ion production rates in SF6 and the relevance thereof to gas-insulated switchgear

Breakdown of SF6 is of commercial interest as a result of the large amounts of SF6-insulated switchgear installed world wide and is of technical interest as a result of the excellent dielectric strength of the gas caused by its high electronegativity. Previous studies in the area of positive surge breakdown area have centered on the concept of “critical volume”. The basic idea has been that probability of breakdown depends on the volume stressed above the minimum breakdown voltage and the electron production rate [1-2]. These concepts are semi-empirically based and have been derived under relatively homogeneous field conditions. As such, one has no reason to think that the concepts have any fundamental or universal validity.