Muti-Field Analysis Of Novel Axial Magnetic Field Contacts For Vacuum Interrupters

Vacuum circuit breaker is widely used in electric power system. As a key component of the vacuum circuit breaker, the vacuum interrupter can directly affect performance of the vacuum circuit breaker. Currently, the vacuum interrupters widely used are designed with axial or radial magnetic field structure to improve the breaking capacity of vacuum circuit breaker. When breaking the short-circuit current, electrode structure with axial magnetic field can increase the limits of short circuit current, under which vacuum arc can burn at its diffuse form. The diffuse vacuum arc will contribute to extinguishing the vacuum arc, so that the breaking capacity of vacuum circuit breaker can be improved.In this paper, a novel asymmetric electrode structure for vacuum interrupters that can induce axial magnetic field is presented. The difference between asymmetric and traditional symmetric electrode structure applied to induce axial magnetic field is that the static contact system has a field coil, but the moving contact system has no any coil. The axial magnetic field between the two contacts is generated only by the static contact system. As the static contact system is stationary components, it is allowed the axial magnetic field coil with relatively complex structure to set on the static contact system. However, the structure of the moving contact should be designed as simply as possible, so that the quality of moving contact can be reduced and contact breaking rate can be increased. With the desired axial magnetic field, using this asymmetry axial magnetic field electrode structure can greatly enhance the mechanical strength of the vacuum interrupter contact system, and help to improve the life of vacuum circuit breakers as well.To analyze the characteristics of the novel asymmetric axial magnetic field contact structure, 3-d finite element method has been adopted. Furthermore, two kinds of design options to improve the axial magnetic field strength are proposed: the first option with an iron core in the static contact system and the second one with two section series connecting coil in plane layout. According to above vacuum interrupter contact structure, 3-d simulation of axial magnetic field at limit breaking current and residual magnetic field at breaking current zero have been carried out. The results show that the novel asymmetric axial magnetic field electrode structure and its improvement two structures have strong magnetic field density and uniform magnetic field distribution. The delay time of residual magnetic field is small. The conductor resistance of contact system can be limited in the allowable range.