The dynamic process of arc pressure and corresponding arc column expansion, which is the main feature after arc ignition and has a significant effect on the breaking behaviour of low -voltage circuit breakers, is studied. By constructing a three dimensional mathematical model of air arc plasma and adopting the Control Volume Method, the parameters of arc plasma including temperature and pressure are obtained. The variations of pressure field and temperature field with time are simulated. The result indicates that there are six stages for the process of arc column expansion according to the variation of pressure in arc chamber. In the first stage, the maximal pressure locates in the region close to cathode, and in the second stage the maximal pressure shifts to the region close to the anode. In the third stage, the pressure difference between the middle of arc column and the ambient gas is very large, so the arc column begins to expand apparently. In the fourth stage, the pressure wave propagates towards both ends and the maximal pressure appears at the two ends when the pressure wave reaches both sidewalls. In the fifth stage, the pressure wave is reflected and collides in the middle of the arc chamber. In the last stage, the propagation and reflection of pressure wave will repeat several times until a steady burning state is reached. In addition, the experimental results of arc column expansion, corresponding to the arc pressure variation, are presented to verify the simulation results.
The influence of copper vapor on the low-voltage circuit breaker arcs is studied. A three-dimensional （3-D） magnetohydrodynamics（MHD） model of arc motion under the effect of external magnetic field is built up. By adopting the commercial computational fluid dynamics （CFD） package FLUENT based on control-volume method, the above MHD model is solved. For the mediums of air-1% Cu and air-10% Cu, the distributions of stationary temperature, pressure, electrical potential and the arc motion processes are compared with those of a pure air arc. The copper vapor diffusion process in the arc chamber and the distribution of copper vapor mass concentration are also simulated. The results shows that the copper vapor has a cooling effect on the arc plasma and can decrease the stationary voltage as well. Moreover, the presence of copper vapor can decelerate the arc motion in the quenching chambers. The maximal copper vapor concentration locates behind the arc root because of the existence of a ＂double vortex＂ near the electrodes.
