Vacuum circuit breakers (VCBs) are widely used in power distribution systems. When the VCB in a switchgear interrupts the short circuit current, the U type loop, which consists of a vacuum interrupter, an external busbar and a conductive rod, generates an external transverse magnetic field (ETMF). This field deflects the vacuum arc and affects the interruption performance of the VCB. In this paper, the real magnetic field data of the arc region are obtained by establishing a simulation model of an electrode system, taking into account the real ETMF and real axial magnetic field (AMF). Furthermore, the three dimensional steady magnetohydrodynamic model of the vacuum arc is established by using real magnetic field data as the boundary condition. The vacuum arc characteristics under the combined effect of AMF and the asymmetric transverse magnetic field (TMF) are studied. The simulation results show that the ETMF considerably changes the Bx of the arc column, which demonstrates asymmetry in the positive and negative directions, whereas By demonstrates a weaker asymmetry. Moreover, the asymmetric TMF deflects the distributions of the vacuum arc plasma and increases the partial heat flux density and axial current density. With the increase in the severity of the short circuit, the TMF asymmetry of the arc region is enhanced and the deflection of the vacuum arc plasma is also enhanced.

In a switchgear, an external transverse magnetic field (ETMF) is generated by the U type loop consisting of the vacuum interrupter, external busbar and conductive rod connected to the vacuum interrupter. The ETMF will make the vacuum arc deflected and strengthen the contraction of the arc. This can increase the probability of breaking failure. To weaken the adverse effect of the ETMF, the real magnetic field data of the arc area with different structure parameters when the length of conductive rod, external busbar and phase distance is changed are obtained by establishing simulation model in this paper. Taking the real magnetic field data as the boundary condition, this paper obtains the typical parameters of the vacuum arc plasma with different structure parameters by using the established three-dimensional high-current vacuum arc magnetohydrodynamics model. The simulation results show that the ETMF makes the transverse magnetic field (TMF) of the arc area asymmetric, which leads to an arc deflection. Reducing the length of the conductive rod connected to the vacuum interrupter to 50 mm can effectively improve the asymmetry of the TMF caused by the EMTF, weaken the arc deflection phenomenon, make the distribution of the plasma parameters more uniform, and increases the utilization of the anode contact surface. Moreover, it can not only reduce the heat flux density into the anode as a whole, but also reduce the heat flux density in the high heat flux density area, so as to effectively reduce the degree of anode activity and improve the negative effects caused by the anode activity. The changes of other external structural parameters have less influence on the improvement of the vacuum arc deflection phenomenon. Increasing the phase spacing to 275 mm or reducing the length of the external bus bar to 100 mm can only slightly weaken the arc deflection.

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