Rate coefficient and collision frequency for electron collision process in hot SF6 gas under electric field: electrical breakdown property at 300–3000 K

Abstract

Hot SF6 gas of several thousand kelvins is produced during the current interruption process in a gas circuit breaker. If the hot gas is subjected to an electric field, electrical breakdown of the hot gas can occur as a consequence of the ionization and attachment processes by electron impact. The probability of occurrence of the process is stated in terms of a rate coefficient. First, this paper describes the rate coefficients of the electron impact processes in the hot SF6 gas subjected to an electric field. The rate coefficients in SF6 gas in the range 300–3000 K at 0.6 MPa are evaluated for 21 processes such as SF4 + e → SF4+ + 2e and F2 + e → (F2−)* → F− + F. Second, using these rate coefficients we obtain the collision frequencies of the 21 processes and find out the predominant processes in the hot SF6 gas. Finally, 26 continuity equations with the rate coefficients are expressed in terms of the particle number densities. Using numerical solutions of the continuity equations, we derive the critical electric field of SF6 gas for different temperatures. Furthermore, comparative discussions are presented on the critical electric field strength and the collision cross‐sections shown in other published papers. The present study is considered to provide the rate coefficients and the critical electric field strengths with higher accuracy. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.