Design And Electromagnetic Simulation Of A New Type Cup-shape Axial Magnetic Field Vacuum Interrupter

Vacuum circuit breakers(VCBs) have been widely applied in the field of medium voltage power system. The development trend of VCBs includes miniaturization, high voltage and large capacity. As a key component of VCBs, design and manufacturing of vacuum interrupter receive highly attention from scholars both at home and abroad. Magnetic control technology is usually used for improving the performance of vacuum interrupters, which includes transverse magnetic field(TMF) and axial magnetic field(AMF). The AMF can reduce loss of arc plasma radial energy and the arc voltage, therefore, the breaking capacity of vacuum interrupter can be improved. Research results show that iron core can not only enhance the magnetic field, but also can change the distribution of magnetic field, which is beneficial to the reliability of vacuum interrupter. A large capacity vacuum interrupter with iron core is designed, the electric and magnetic fields of which are simulated by finite element analysis software.First of all, a model for TD-12/3150-40 vacuum interrupter is designed. The size of insulation shell, contact, shield, corrugated pipe and other parts are computed based on the empirical formula. Meanwhile, the suitable materials are selected. The shield structures with rolled edge and without rolled edge are designed respectively.Secondly, a series of mathematical models for electric field calculation are established and a two-dimensional axial symmetry model of vacuum interrupter is built up. The vacuum interrupter internal potential and electric field are computed by the finite element analysis software. The distribution of potential and electric field of the two kinds of shield structure are analyzed. The distribution of electric fields on the moving contact surface, static contact surface and shield inner surface are compared and analyzed. The simulation results show that the shield structure with rolled edge performs much better than the one without rolled edge.At last, the three-dimensional models of vacuum interrupter contact are built up, which include one contact without iron core, one contact with annular iron core, and three contacts with columnar iron cores. The numbers of columnar iron cores are 8, 10 and 12. Transient magnetic field of different contacts are simulated using three-dimensional finite element analysis software, and eddy current effect is considered. With the current at peak value and zero, the AMF distribution on stationary and moving contact surfaces and on the mid-gap plane between the two surfaces are calculated, as well as the lag time of AMF. The simulation results show that magnetic field strength is enhanced with iron core added, and the lag time of AMF becomes larger as well. According to the comparison of simulation results, it can be seen that the contact with 12 columnar iron cores has large magnetic field strength and uniform magnetic field distribution at peak current; less residual field and short AMF lag time after current zero-crossing. In summary, the contact with 12 columnar iron cores owns the best performance.