In order to investigate the distribution and influence of the unbalanced magnetic field（BMF） in multi-break VCBs

the concept of the magnetic arc blow in multi-break VCBs is firstly proposed and the magnetic arc blow is caused by unbalanced magnetic field which is produced by the interaction between each breaks and the connection bus is analyzed. The magnetic field model of the double-break VCBs in different configurations is established. The magnetic field distribution is calculated by the Ansoft Maxwell. Based on the simulation data of the magnetic field in double-break and single-break VCBs

the vector calculation is used to calculate the unbalanced magnetic field. The laws of the unbalanced magnetic field influenced by the configuration and vacuum arcs are obtained. The simulation results indicate that the BMF of the double-break VCBs is below 30 mT with different configuration and distance when the main current is 10 kA.The BMF decreases as the distance of the vacuum interrupters in double-break VCBs. The magnetic field shield

which is achieved by smearing the magnetic material on the copper shield

is proposed to restrain the BMF in double-break VCBs.The BMF and optimal method is obtained which is useful to the configuration and optimization design of the multi-break VCBs from the aspect of the magnetic field distribution.