Characteristics of PTFE ablation due to SF6 arc exposure were studied to predict the ablated mass of PTFE nozzle in high‐voltage circuit breaker. From the measurement of the ablated mass, the predominant factor of the PTFE ablation was revealed as a radiation power of SF6 arc. Subsequently, the radiation power absorbed in PTFE was formulated on the basis of the radiation transfer property and the arc physics. The formulation for the prediction of the PTFE ablated mass was established with the formulated radiation power and the measured masses. Finally, the validity of the PTFE ablated mass prediction was shown from the results of the error verification with the measured masses.

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Hot SF 6 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 SF 6 gas subjected to an electric field. The rate coefficients in SF 6 gas in the range 300-3000 K at 0.6 MPa are evaluated for 21 processes such as SF 4 + e → SF 4 + + 2e and F 2 + e → (F 2 − ) * → 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 SF 6 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 SF 6 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.

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