• Conclusion

In this paper, which can be separated into two broad sections, we firstly present a study of the chemical kinetics of SF6, then we present a hydrokinetic model. The kinetic study brought out the following points: from the study of the reaction rates, we showed that polyatomic molecules cannot penetrate into the hot regions containing the electrons. However, the penetration of S2 molecules leads to an overpopulation of S2+ which traps electrons. The hydrodynamic model, using simplified geometry, predicts the occurrence of electron under-population in regions where the temperature is between 4000 and 6000 K, a critical temperature range for thermal cut-off in SF6 circuit breakers. The study has shown that the disappearance of electrons can be explained by electron-ion recombination with S2+ molecules and that this effect is enhanced by cold gas convection. This paper is the first step in the study of deviations from equilibrium in models of decaying circuit-breaker arcs. Now, we are developing a two-temperature model that may include deviations from thermal equilibrium occurring when a recovery voltage is applied to the decaying arc plasma.

• Acknowledgments

This work was partly financed by a contract with Electricité de France (EDF) and GEC-Alsthom.