Analysis of axial magnetic field of an iron style bipolar axial magnetic field vacuum interrupter

An axial magnetic field (AMF) electrode for a vacuum interrupter iron style bipolar electrode (ISBE), is improved in order to distribute vacuum arc over contact plate as much as possible and reduce eddy current in iron cores. The improvements include increasing iron core area to the edge of contact plate and using laminated iron core (1.2 mm in our case), based on analysis of AMF in the gap and eddy current in iron cores. AMF measurement results show that axial magnetic flux density of improved ISBE is almost two times stronger than that of original one, and there is only a little loss at edge of contact plate. However, the axial magnetic flux density of original ISBE at edge of contact plate is much lower. The vacuum arc picture recorded by a high speed CCD camera proves that AMF of improved ISBE has ability to distribute vacuum arc over most area of the entire contact surface, even at the edge region. Eddy current induces phase shift. The maximum value of phase shift in middle plane of contact gap of the original ISBE is 3.5 ms and it is reduced to 2.0 ins in the improved one, which is similar to other AMF electrodes.