Simulation Research Of Axial Magnetic Field Vacuum Arc Plasma

Vacuum circuit breakers are widely used in medium-voltage transmission and distribution systems, and will be increasingly applied in high-voltage field in future. The breaking characteristics and controlling measures of vacuum arc are the key points of design and manufacture of vacuum circuit breakers. Meanwhile, modeling rationally and simulating correctly are effective means to study further on vacuum arc. This paper will focus on the simulation of vacuum arc plasma model which considering axial magnetic field and the results will provide a certain theoretical basis for the design of vacuum circuit breaker.Based on the analysis of the existing vacuum arc models, the magentohydrodynamic (MHD) model of axial magnetic field vacuum arc is derived, in which the influence of the average ion charge number and ion kinetic energy term on the vacuum arc are also considered. The vacuum arc plasma is not in a local thermodynamic equilibrium state, and energy exchange between ion and electron is existed due to collide with each other there, therefore, ion and electron should be calculation separately. Energy conservation equations of ion and electron are used to solve ion temperature and electron temperature respectively. In addition, the plasma as a conductive fluid will produce magnetic field which reacting on the vacuum arc and affecting the flow of plasma in the motion, so the calculation of self-magnetic field is crucial. In the model, self-magnetic field distribution will be solved by the magnetic vector potential method.The MHD model of axial magnetic field vacuum arc is a set of nonlinear partial differential equations that coupled each other, and the traditional analytical methods are unable to solve such problems, so numerical methods must be used. Computational fluid dynamic (CFD) software FLUENT is selected as a platform for the solution of arc model and self programming languages VC++ and custom macro function are applied to its second development, numerical simulation of vacuum arc plasma under axial magnetic field is realized successfully. Based on the simulation of the low current vacuum arc, the influence of AMF on important plasma parameters is studied. The simulation results show that the influence of AMF on low-current vacuum arc plasma parameters is different from that of high current vacuum arc. In the case of low current, with the axial magnetic field increases, the diffusion of vacuum arc is reduced and the parameters such as axial current density, ion temperature, electron temperature and plasma pressure are increased. Therefore, it is inappropriate to apply a too strong axial magnetic field to the vacuum arc when the interrupting current is low.