Considering that the arcing process of a rotary arc load switch is truly three dimensional（3 D）in nature

commercial computational fluid dynamic software FLUENT has been adapted and extended by self-written routines to establish the 3 D arc simulation model to perform 3 D arc dynamic simulation based on the magneto-hydrodynamic（MHD）theory.The motion characteristics of arc and the influence of magnetic field produced by electric current on arc motion during arc ignition of rotary arc load switch are simulated and analyzed.The results show that the arc rotates at high speed under the influence of the Lorenz force produced by the magnetic field

and the stationary arc leads to the low breaking capacity of the arc chamber

while the high speed rotation of the arc increases the interrupting capacity of the arc chamber.The experimental results of arc motion prove the accuracy of arc simulation method.