Ionization and attachment coefficients in C4F7N/N2 gas mixtures for use as a replacement to SF6

C
₄
F
₇
N/N
₂
gas mixtures are considered as new candidate insulation gases to replace SF
₆
. In this study, the Townsend first ionization coefficient α and the attachment coefficient η were measured in C
₄
F
₇
N/N
₂
gas mixtures using the steady-state Townsend method over a range of electric fields E/N from 200 to 500 Td. The C
₄
F
₇
N 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% C
₄
F
₇
N/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 C
₄
F
₇
N/N
₂
gas mixtures with C
₄
F
₇
N content varying from 7.00 to 13.10% may be an appropriate substitute gas for SF
₆
in electrical industry applications.