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.