Some Computations and Observations on Corona-Stabilized Breakdown in SF6

Loeb retracted his support for Hermstein's negative ions cloud theory and proposed that the reduction of electric field at the anode, due to the presence of positive ions space charge, could be responsible for the corona-stabilization in electronegative gases. Based on this comment, Abdel-Salam et al. proposed a semi-empirical criterion for the calculation of the breakdown voltage during corona-stabilization. It is shown in this paper that this criterion, which is based on the avalanche growth in the presence of space charge field, would not work. We computed several discharge parameters such as the total charge, the current flowing and the power dissipated in the gap at experimental breakdown voltages in coaxial cylinders and concentric spheres gaps. The corona onset voltages were also calculated based on the streamer theory. The purpose was to explore if a new, simple and reasonably accurate semi-empirical criterion for the calculation of the breakdown voltage could be established. Results indicate that the calculated values of the corona onset voltage agreed well with the experimental results but no simple equation can correlate the discharge parameters, the field non-uniformity, the gas pressure and the breakdown voltage.