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Modélisation de l'extinction d'un arc de SF6 hors d'équilibre thermodynamique local

Abstract : During the circuit-breaker arc decay, a rapid diminution of the conductance of the arc is observed, subjecting the plasma produced in very high convection fields which may introduce departures from chemical equilibrium. The existing models, based on local thermodynamic equilibrium assumption point out this effect but do not consider all the mechanisms susceptible to occur during extinction. The convection may be responsible for the presence of cold gas, partially dissociated in the warmer regions of the plasma. The cold particulate recombine rapidly with the electrons leading to a change in the resistivity of the environment. For a better understanding of this phenomenon, we have developed a simplified 2D model of a SF6 arc during extinction. This model associates both chemical kinetic and hydrodynamic models, permitting the calculation of the number densities of the different species present in the plasma. Beforehand, the composition of the plasma is obtained from a collisionnal model and hydrodynamic code in stationary regime was developed to initialise the temperature and the velocity fields. This model was completed thereafter by a study of the chemical kinetics of SF6 which allowed us to single out the different reactions which govern the disappearance of the electrons. We have simulated the extinction of the arc for a current intensity I = 50 A and for pressure of 0.1 and 0.4 MPa. The kinetic model is linked with the hydrodynamic one from Dalton's equation and from the relation associating the mass density to that of the species number densities. The principal results of the hydrodynamic code affirm that the cooling rate is about -108 K.s-1. The kinetics results indicate that convection affects S2 molecules, found on the edge of the discharge and for temperature ranging from 4000 K to 6000 K, which are overpopulated compared with that of equilibrium. Due to the charge exchange between S2 and S+ an overpopulation of S2 leads to overpopulation of S2+. These ions basically recombine with the electrons causing a lowering of the electron population and thus a modification of the resistivity.
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https://tel.archives-ouvertes.fr/tel-00003150
Contributor : Jean-Belkheir Belhaouari <>
Submitted on : Wednesday, July 23, 2003 - 6:36:47 PM
Last modification on : Friday, January 10, 2020 - 9:08:17 PM
Long-term archiving on: : Monday, September 20, 2010 - 11:34:40 AM

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  • HAL Id : tel-00003150, version 2

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Jean-Belkheir Belhaouari. Modélisation de l'extinction d'un arc de SF6 hors d'équilibre thermodynamique local. Physique [physics]. Université Paul Sabatier - Toulouse III, 1997. Français. ⟨tel-00003150v2⟩

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