During extinction there is strong arc blowing
leading to turbulence phenomena. The mechanisms involved are
responsible for the energy transfer necessary for the recovery of
dielectric rigidity. So a model based only on thermal phenomena cannot
explain the behaviour of the plasma where chemical non-equilibrium
exists as a result of turbulence or strong cooling (-10E8 K.s-1 ). All
the models based on the hypothesis of LTE lead to a post-arc current,
unlike in experimental results where post-arc current is often
non-existent after the zero of the alternating current. To interpret
this difference, we have to consider that molecular species may be
present in the hot regions. So, the plasma column could be cut by a
portion of gas with low electrical conductivity hindering the
circulation of electric current.

The general aim of this work is to simulate
decaying arc behaviour taking non-equilibrium effects into account. The
aim of the work is not to modelize exactly the behaviour of a circuit
breaker and to represent all the arc life evolution (creation, high
current, decrease of the intensity, evolution near current zero, post
arc phase and the dielectric phase), but to study the post arc phase of
the thermodynamic plasma without an application of an RRRV (Rate of
Rise of Recovery Voltage). So, we built a mathematical model which
couples, in simplified geometry, a hydrodynamic and a kinetic study for
an SF6 gas in a two-dimensional flow in a transient state at a pressure
of 10E5 Pa. Coupling between hydrodynamics and kinetics is achieved
through the pressure and the mass density.

The work is divided into three parts. The first,
presents the SF6 plasma composition in stationnary state. The second
part focuses on the study of SF6 kinetics. Here, we study the species
involved in the processes leading to electron disappearance and those
that may be influenced by the strong convection brought about by arc
decay. In the third part, we present the foundations of the
hydrokinetic model such as the assumptions made, the geometry and the
boundary conditions as well as all the equations that enable us to
calculate the profiles of temperature, velocity and density over time;
the results are then analysed considering the departures from
equilibrium.