Ionization and attachment coefficients in C 4 F 7 N/N 2 gas mixtures for use as a replacement to SF 6

C4F7N/N2 gas mixtures are considered as new candidate insulation gases to replace SF6. In this study, the Townsend first ionization coefficient α and the attachment coefficient η were measured in C4F7N/N2 gas mixtures using the steady-state Townsend method over a range of electric fields E/N from 200 to 500 Td. The C4F7N concentrations studied were 5.07, 7.00, 13.10 and 19.09%. In addition, the effective ionization coefficients and the critical electric field were also obtained. A comparison of the experimental results with those for SF6 gas indicates that 19.09% C4F7N/80.91% N2 provides better insulation performance with a higher normalized critical electric field of 395 Td. However, when the liquefaction temperature is considered, the C4F7N/N2 gas mixtures with C4F7N content varying from 7.00 to 13.10% may be an appropriate substitute gas for SF6 in electrical industry applications.