Thesis - Simulation of a decaying SF6 arc plasma

  • Thesis

My thesis work was defended the 1997 November 25 in the "Centre de Physique des Plasmas et Applications de Toulouse". The CPAT is a laboratory on the campus of the University Paul Sabatier in Toulouse, France which is sponsored jointly by the CNRS (Centre National de la Recherche Scientifique) and the University. The subject of this thesis to relate the simulation of decaying SF6 arc plasma (non equilibrium kinetic). This work is supported partly by Gec-Alsthom and is part of the global study of the modelling circuit breaker utilised on the EDF town mains. I propose you to share my acquaintance on arc plasma and I invite you to contact me.

  • Abstract

During the decay of a circuit-breaker arc, the plasma is subjected to strong blowing which can lead to deviations from chemical equilibrium. The intense convection may therefore be responsible for the presence of cold gas in the hot parts of the plasma. The cold particles then rapidly recombine with electrons, modifying the resistivity of the plasma. In order to study this phenomenon as it appears in circuit-breakers, we modelled the extinction of an SF6 arc for a simplified geometry. The 2-dimensional model that was set up was furthered by a study of the kinetics of SF6 which enabled us to identify the various reaction processes governing the disappearance of electrons. The results show that convection acts on S2 molecules which, at the edge of the discharge and for temperatures of between 4000 and 6000 K, are overpopulated with respect to equilibrium. Through charge exchange processes between S2 and S2+ particles, the overpopulation of S2 leads to an overpopulation of the S2+ ions. These ions mainly recombine with electrons, lowering the electron population and modifying the electrical conductivity of the plasma.

  • Mathematical model

  • Temperaturefields(t=0ms-50ms)(movie2D).

    Temperature fields ( t = 0 ms - 50 ms) (movie 2D).

    • Circuit breaker