On the calculation of breakdown voltages for uniform electric fields in compressed air and SF/sub 6/

A novel method is described for calculating the breakdown voltage of uniform field gaps in compressed air and SF/sub 6/ 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 SF/sub 6/) 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.<>