3D Simulation of Air Arc in the Molded Case Circuit Breaker

Abstract

In low voltage switch gears, the arc voltage is a very important factor that decides the interruption performance. There are several ways to increase the arc voltage, like increasing the number of the arc chutes or the distance between the contacts. During the interruption, the separation of the contacts plays an important role in different kinds of switch gears since the arc motion or the arc elongation will be effected. However, the simulation of the arc behavior in low voltage switch gears is quite difficult due to the fact that: the 3D simulation makes the computation quite expensive; the existence of the arc chutes makes the calculation non-linear; the structure of some switch gears could be quite complicated. Therefore, the movement of the contact was neglected for simplicity. In fact, the movement of the contact could increase the arc length and then decide the arc behavior. In reverse, the arc current will be changed during the interruption and the Lorentz force will then influence the movement of the contact. It is necessary to consider this phenomenon to make the arc simulation more accurate and universal. In this work, low voltage arc plasma simulation in 3D with contact opening process has been established. Both the sheath and nonlinear magnetic material are taken into consideration. Calculation is based on magneto-hydrodynamic arc model, a method for coupling different software to separately calculate fluid and electromagnetic field has been developed to fulfill the requirements above. Furthermore, a low voltage circuit breaker has been experimented to compare with the simulation from U-I characteristics. The simulation results suggest that this method applied in arc simulation performs better in converging and accuracy.