Determination of the Transport Coefficients of an Air Plasma Contaminated by AgSnO2 Alloy Vapour

The physicochemical properties of the electric arc determine the success or failure of the electric current by the circuit breaker. This work is devoted to the determination of the transport coefficients of air plasma contaminated by silver tin(IV) oxide (AgSnO2) alloy electrical contact vapour in a low voltage circuit breaker. It aims to theoretically evaluate the influence of AgSnO2 alloy electrical contact material on the electrical current breaking capacity of the low-voltage air circuit breaker through the electrical conductivity, thermal conductivity and dynamic viscosity of the plasma air-AgSnO2. They are determined over a temperature range from 500 K –30,000 K, at atmospheric pressure and at local thermodynamic equilibrium. The analytical expressions necessary to determine these transport coefficients of the air-AgSnO2 mixture plasma are deduced from the Boltzmann equation using the approximate Chapman-Enskog method. Analyses of the obtained results show that, for the same given temperature, the electrical conductivity increases significantly when the AgSnO2 alloy vapour increases in the mixture for temperatures below 11,000 K. The dynamic viscosity of the plasma decreases as the percentage of AgSnO2 alloy electrical contact vapour increases in the mixture, for temperatures below 12,000 K. In the temperature range from 500 K–20,000 K, the total thermal conductivity of the plasma decreases as the percentage of AgSnO2 alloy electrical contact vapour increases in the mixture. It results that increasing the percentage of electrical contact vapour in AgSnO2 alloy will slow down the extinction of the electric arc created inside the circuit breaker, especially beyond 0.1% of vapour. This slowing down of the extinction of the electric arc can cause the circuit breaker to fail to cut off electrical current.