Study of the Equilibrium Composition of an Air Plasma Contaminated by H 2 S, Cl 2 , and SO 2

Dust and corrosive atmospheres severely impact the dielectric strength of the switching chamber and moving parts in air circuit breakers. Within the arc-quenching chamber, the switching medium must possess sufficient deionization capability to ensure its dielectric recovery. However, this capability can be significantly compromised by the presence of corrosive species such as H 2 S, Cl 2 , and SO 2 . These impurities can lead to an increase in contact resistance through contact corrosion, as well as the generation of leakage currents. Thus, the objective of this study is to highlight the impact of H 2 S, Cl 2 , and SO 2 species on the equilibrium composition of air plasma at atmospheric pressure and under local thermodynamic equilibrium (LTE) conditions. The Gibbs free energy minimization method is used to determine the plasma equilibrium composition. The results reveal a complete modification of the plasma equilibrium composition due to the presence of these impurities, characterized by the formation of species such as Cl 2 , S 2 , NOCl, HCl, HOCl, H 2 , SH, S 2 O, HO 2 , ClO, SO 3 , SO 2 , NO, SO, SCl and SN, whose concentrations vary depending on the impurity percentage. It is shown that the presence of HCl and Cl 2 accelerates contact corrosion. Furthermore, a significant increase in electron density is observed between 5,000 K and 14,000 K. This phenomenon induces a rise in electrical conductivity, which could ultimately lead to a current interruption failure.