Equilibrium Composition of a Plasma in the Low Voltage Air Circuit Breaker Contaminated by the Vapor of AgSnO<sub>2</sub> Alloy Electrical Contacts

Abstract

When the circuit breaker cuts the electric current, an electric arc is created between its electrodes. The success or failure of breaking the electric current by the circuit breaker depends strongly on the physico-chemical properties of the electric arc created, such as the composition of which depends on the material of the electrical contacts. In this work, we determine the equilibrium composition of the electric arc in the low voltage air circuit breaker with silver tin dioxide alloy contacts, in a temperature range from 500 K to 15,000 K and at atmospheric pressure. We use the Gibbs free energy minimization method and develop a computer code to determine the equilibrium composition of the created plasma. The analysis of the results obtained shows that O2 particles with a dissociation energy of 5.114 eV, NO with a dissociation energy of 6.503 eV, and N2 dissociation 9.756 eV dissociate around 3500 K, 5000 K, and 7500 K, respectively. We note that the electro-neutrality is established between the electrons and the cations: Ag+ and NO+, for temperatures lower than 6500 K. For temperatures higher than 6500 K, the electro-neutrality is established between the electrons and the cations: N+, O+, and Ag+. The numerical density of the electrons increases when the proportion of the vapor of the electrical contacts increases in the mixture, in particular for temperatures lower than 11,000 K.