Abstract
This work is related to the chemical kinetics modelling of plasma during extinction. A zero-dimensional model (0D) has been developed. Two hypotheses were used: (A) a constant pressure or (B) a constant mass density. Three initial data categories are generally required for the model: (1) the chemical reactions that govern the kinetic scheme, (2) the chemical composition at the local thermodynamic equilibrium (LTE) and (3) a law of temperature decay as a function of time representing the cooling rate. The developed model is presented and applied to SF6, gas commonly used in high voltage circuit breakers (HVCB), in order to be validated. We present the evolution of the species during the temperature decay for several cooling rates. The results give the evolution of species densities and the departures from equilibrium according to the cooling rate. Consideration of SFx molecules is essential in order to avoid erroneous interpretations.
Highlights
The study of chemical kinetics is essential in order to know the evolution of the species, the predominant reactions or even the differences that may exist in relation to the Local Thermodynamic Equilibrium (LTE) hypothesis
In order to have the densities at local thermodynamic equilibrium (LTE) according to these two hypotheses and to allow studying the departures from equilibrium, the plasma composition was calculated according to the same hypotheses
We have shown under the conditions of this study that the evolution of pressure deduced from the species densities of the kinetic model evolves in equilibrium
Summary
The study of chemical kinetics is essential in order to know the evolution of the species, the predominant reactions or even the differences that may exist in relation to the Local Thermodynamic Equilibrium (LTE) hypothesis These deviations depend on the initial and operating conditions such as pressure, temperature, gases involved or the cooling rate. In switching devices such as High Voltage Circuit Breakers (HVCB), the main interest is in the electronic densities present during the transition by the current zero in order to study the evolution of conductance as a function of time and the dielectric recovery [4]. At this tempertaure, depending on the colling rate the electronic density can lead to residual electrical conductivity and so to a shutdown failure
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