Breakdown fields in synthetic air, CO2, a CO2 / O2 mixture, and CF4 in the pressure range 0.5–10 MPa

The breakdown electric field strength in synthetic air, CO
2
, a mixture of CO
2
and O
2
, and CF
4
was investigated under conditions relevant for high voltage insulation systems, specifically, in nearly uniform fields and using electrodes with technical surfaces. The results show a saturation of the breakdown electric field strength above 2 MPa; this effect can be explained by streamer inception calculations. The lowest saturation breakdown electric field strengths are similar for the different gases and are in the range of 200 to 300 kV/cm. There is no change in the breakdown electric field strength if the gas becomes supercritical. This indicates that particle number density and the surface structure is the main controlling parameter for the breakdown in the investigated parameter range.