Numerical modeling of CO2 arc based on the non-chemically equilibrium effect

Carbon dioxide (CO2) and its mixtures are potential alternatives as the arc quenching medium in switchgear. During the arc decaying phase after the arc current drops to zero, the arc plasma will deviate from the local thermally equilibrium (LTE) state and then the non-chemically equilibrium (non-CE) effect should be considered to predict the arc behavior. A non-CE numerical model was established to investigate the dynamic behavior of CO2 arc during the current zero (CZ) period. The time-dependent distributions of temperature, energy and electrical conductivity between the LTE and non-CE models were compared. The distributions of the species compositions and the non-equilibrium parameters were also investigated to further explain the mechanism of the non-CE effect. The non-CE particle transport is the main reason for the difference of temperature decay between non-CE and LTE calculations. The transport of all particles at the edge of the arc is dominantly influenced by the radial convection and diffusion, while the transport of atoms at the arc center is the combined results of convection, diffusion and chemical kinetics. As a contrast, the transports of electrons and ions are dominated by the chemical reactions. The decay of electron density at the nozzle throat calculated by the non-CE model are in good agreement with the laser Thomson scattering tests, while the LTE model failed to predict the electron density accurately, which proves that the non-CE effect of CO2 arc during CZ period cannot be ignored.