On the calculation of breakdown voltages for uniform electricfields in compressed air and SF6

A novel method is described for calculating the breakdown voltage of uniform field gaps in compressed air and SF₆ without the need for experiments. This method is based on the criterion of self-recurring single-electron avalanches developed in the gap. It is shown that the results computed by this method for pd values to the right of Paschen's minimum (up to 15 kPa·m in air and up to 5 kPa·M in SF₆) are in good agreement with those measured experimentally. It is also shown that the use of the streamer criterion overestimates the breakdown voltage when applied for pd values where Townsend's mechanism is valid. In addition, it is shown that the size of the avalanche (and hence the parameter K) at breakdown is not constant as adopted in the literature; it depends upon the gap length and gas pressure