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After current zero in a high-voltage SF6 circuit breaker, the recovery voltage heats the remaining electrons, producing departures from thermal equilibrium that may modify the electrical conductivity of the medium and thus the interruption capability of the apparatus. In this study we present a two-temperature hydrodynamic model coupled with a kinetic model, applied to the extinction of a blown SF6 arc in a two-dimensional simplified geometry. The free decay and the post-arc phase with the recovery voltage have been studied. The kinetic part of the modelling allows us to calculate the evolution of the electron number density. A simplified turbulence model has been added to study its influence on the post-arc phase. The main results of this study reinforce the conclusions obtained taking into account only the chemical non-equilibrium: the departures from equilibrium tend to decrease the interruption capability predicted by the model. This effect is due to the weak energy exchange by elastic collisions between the electrons and the heavy particles, leading to an electron temperature higher than the gas temperature which favours the ionization of the medium submitted to a recovery voltage.

Studying the influence of thermal departures from equilibrium in SF 6 circuit-breakers, we develop a two-temperature kinetic model to calculate the composition. Such a kinetic approach has not been adopted until now for SF 6 plasma because of the complexity of chemical processes. Our model takes into account the collisional mechanisms responsible for the creation and disappearance of atoms and molecules through 19 species linked by 66 chemical reactions. To solve the conservation equations, the model uses the direct rates of reactions, that mainly proceed from the literature, and reverse rates, that are computed by two-temperature micro-reversibility laws. Thus, we point out the importance of the choice of the expression of Saha law, comparing Potapov and van de Sanden formulations of this law. We then discuss the impact of thermal departures from equilibrium on plasma composition, on 'mean path' of molecules before dissociation in the plasma, and on the reactions that govern the disappearance of electrons.Disappearance frequency of species A through reaction 'p' (s −1 ) ν ATotal disappearance frequency of species A (s −1 ) θ Ratio between electrons temperature and heavy particles one (θ = T e /T h ) hPlanck constant (J s) k B Boltzmann constant (J K −1

This paper is the second step in the study of deviations from equilibrium in models of decaying SF6 arcs. The first step was based on a kinetic approach, which allowed us to study the influence of deviations from chemical equilibrium. Departures from equilibrium are shown for a simplified geometry, and we find results similar to those of in the literature for the influence of pressure or intensity. In order to build the basis of the two-temperature model, we calculated the two-temperature composition, the transport coefficients and thermodynamic properties, and the energy exchange term between electrons and heavy particles through elastic collisions. Electron-ion collisions contribute to the main part of the energy exchange term, S+ and S2+ having the greatest contributions to this term. Our results show that taking departures from thermal equilibrium into account leads to a slower cooling rate of the plasma. The evolution of temperature departures during extinction is in agreement with experimental results.