Ionization and Attachment Coefficients in C4F7N Gas Measured by the Steady-State Townsend Method

The normalized Townsend first ionization coefficient α/N and normalized attachment coefficient η/N in pure C4F7N were measured by using the steady-state Townsend (SST) method for a range of reduced electric fields E/N from 750 to 1150 Td at room temperature (20 °C). Meanwhile, the effective ionization coefficients are obtained. All SST experimental results show good agreement with pulsed Townsend (PT) experiment results. Comparisons of the critical electric fields of C4F7N with SF6 and other alternative gases such as c-C4F8 and CF3I indicate that C4F7N has a better insulation performance with a much higher normalized critical electric field at 959.19 Td.