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

Abstract

Carbon dioxide (CO2) and its mixtures are potential alternative gases for arc extinguishing in switchgear. During the arc decaying phase, the non-chemically equilibrium (non-CE) effect leads to the departure from the local thermal equilibrium (LTE) model in predicting the arc behavior. This work is focused on the dynamic behavior of CO2 arc during the current zero (CZ) period. A non-CE numerical model was established. The decay process of temperature, energy and electrical conductivity between the LTE and non-CE models were compared. The distributions of species compositions, non-equilibrium parameters together with the transport process of the particles were further investigated. The change of particle distributions caused by the non-CE effect is the main reason for the difference of temperature decay between non-CE and LTE. The particles transport at the edge of the arc depends on the radial convection and diffusion, while the transport of atoms in the arc core is the combined results of convection, diffusion and chemical kinetics. As a contrast, the transport of electrons and ions is still dominated by 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 (LTS) 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.