A study of the Thermodynamic Characteristics of Air-Cl2-H2S Plasma in an Air Circuit Breaker

The air circuit breaker (ACB) is a reliable protection device that uses ambient air to extinguish electric arcs and interrupt circuits. It is primarily employed in power distribution systems to secure circuits and equipment against overcurrents, short circuits, and faults. Operating in ambient air exposes the device to environmental stressors such as humidity, saline conditions, and dust, with a specific emphasis on corrosive atmospheres. Hydrogen sulfide (H₂S) and chlorine (Cl₂) are corrosive agents that react with metals such as copper, aluminium, and silver. These reactions increase the resistance of insertion contacts, cause excessive overheating, and lead to short-circuiting, which may result in control unit malfunctions. They also contribute to increased friction, mechanical failures, and stainless-steel spring breakages. While previous studies focused on the effects of metal oxides and carbon monoxide present in aerosols, a gap remains regarding the specific influence of corrosive species such as H2S and Cl2. The objective of this study is to assess the impact of H₂S and Cl₂ on the thermodynamic properties of the circuit breaker’s air plasma during the current interruption phase. The Gibbs free energy minimization method is applied to determine the equilibrium composition of the mixture required for the calculation of thermodynamic properties. The results show that the presence of H₂S and Cl₂ increases plasma density while reducing specific enthalpy, heat capacity, and sound velocity.