Inherent Limitations in Uniform Field Discharge Data for SF6

So-called uniform field discharge data for SF6 may be subject to errors caused by the effect of the inherent nonuniformity of the test gap. It is shown that uniform field pre-breakdown measurements of ionization and attachment coefficients in SF6 require pd values below a few hundred mmHg cm, and that pd must be less than a few thousand mmHg cm to obtain proper uniform field breakdown voltages.