Characteristics Of Arc Plasma During The Breaking Of Vacuum Circuit Breaker

With the deepening of sustainable development process,developing environment-friendly transmission grade circuit breakers has become an important trend.Because vacuum circuit breaker is environmentally friendly and has good breaking performance and maintainability,it has attracted more and more attention.How to improve the voltage level of vacuum circuit breaker has always been one of the major issues that attracted worldwide attention.The theory of vacuum arc becomes very complicated because electrode is involved in the process of arc burning.The lack of understanding of vacuum arc characteristics is one of the reasons that restrict the development of vacuum circuit breakers to higher voltage grades.For this reason,in the breaking process of vacuum circuit breaker the characteristics of arc plasma and the anode activity under the action of large current are studied and analyzed by numerical simulation technology in this paper.Firstly,a two-dimensional axisymmetric model is constructed in the inter-electrode plasma area of the vacuum circuit breaker based on the actual structure of the vacuum circuit breaker.According to the continuity equation,momentum equation and energy equation of fluid mechanics,combined with Maxwell's equations,generalized ohm's law and Lorentz force equation,a two-temperature magnetic hydro-dynamic model of subsonic vacuum arc is established.Secondly,with the help of COMSOL Multiphysics simulation software,the characteristic parameters such as ion density,electron temperature,ion temperature,velocity and pressure of arc plasma in the breaking process of vacuum circuit breaker are studied and analyzed,the changes of ion density at different contact distances are also discussed.Thirdly,the magnetic field distribution of a coil structure is studied,and the effect of coil turns on magnetic field strength is discussed.Then,the energy flux density of arc plasma on anode surface was analyzed.Through the numerical simulation of the vacuum arc,the maximum values of ion density,ion temperature,electron temperature and pressure are found near the center of the cathode,while the maximum values of velocity are found near the anode.With the increase of time,the numerical values of characteristic parameters such as ion density,ion temperature,electron temperature,pressure and velocity are improved.When the contact distance increases,the ion density decreases.The magnetic field strength of the coil structure increases gradually from the inside to the outside in the arc extinguishing chamber,the magnetic field strength increases with the number of coil turns increasing.Lastly,in order to analyze the influence of arc plasma on anode activity,the governing equation of anode phase transition process is established in this paper.The enthalpy-porosity method is used to treat the liquid phase ratio.The rate of anode melting is described by Stefan equation,a two-dimensional axisymmetric model was established for the anode contact plate,and the arc energy flow was used as the boundary condition of the heat flow on the anode surface,with COMSOL Multiphysics simulation software,the thermal physics process of anode is numerically simulated.The changes of anode surface temperature and anode melting under the action of arc energy flow were analyzed.The changes of anode surface temperature,molten pool depth and saturated vapor pressure under different energy flows were discussed.