This paper focuses on the numerical investigation of arc plasma behavior during arc commutation process in a medium-voltage direct current circuit breaker （DCCB） contact system. A three-dimensional magneto-hydrodynamic （MHD） model of air arc plasma in the contact system of a DCCB is developed, based on commercial software FLUENT. Coupled electromagnetic and gas dynamic interactions are considered as usual, and a thin layer of nonlinear electrical resistance elements is used to represent the voltage drop of plasma sheath and the formation of new arc root. The distributions of pressure, temperature, gas flow and current density of arc plasma in arc region are calculated. The simulation results indicate that the pressure distribution related to the contact system has a strong effect on the arc commutation process, arising from the change of electrical conductivity in the arc root region. In DCCB contact system, the pressure of arc root region will be concentrated and higher if the space above the moving contact is enclosed, which is not good for arc root commutation. However, when the region is opened, the pressure distribution would be lower and more evenly, which is favorable for the arc root commutation.
This paper focuses on a numerical simulation of the arc plasma behavior in the arc splitting process, considering the eddy currents in the electrodes and the splitter plate. Based on three-dimensional （3D） magneto-hydrodynamic （MHD） theory, a thin layer of nonlinear electrical resistance elements is used in the model to represent the voltage drop of plasma sheath and the formation of new arc root in order to include the arc splitting process in the simulation. In the arcing process, eddy currents in metal parts are generated by a time-varying magnetic field. The arc model is calculated with the time-varying magnetic field term, so that the eddy current effects can be considered. The effect of nonlinear permeability of a ferromagnetic material is also involved in the calculation. Using the simulation results for the temperature, velocity and current density distribution, the arc splitting process is analyzed in detail. The calculated results are compared with the simulation neglecting eddy currents.
