| In recent years,the rapid development of new energy and electric vehicle put forward higher requirements for the ability of breaking the direct current under the condition of load or failure.The traditional DC switchgear can no longer meet its operation requirements,so how to design high-power,small size and better breaking DC switches is urgent.The DC contactor with contacts will be difficult to avoid arcing during the breaking process,and the increase of power will increase the energy of the arc and increase the difficulty of arc extinction.Compared with AC arc,the DC arc has no zero point,and its extinguishing is more difficult is more difficult.Therefore,it is of great practical significance to design the arc extinguishing system and shorten the arc time for the DC contactor to increase the capacity,reduce the volume,improve the breaking capacity and prolong the service life.Based on the magnetohydrodynamic theory(MHD),a mathematical model of DC air arc plasma is established in this paper.By assuming the conditions of arc plasma sheath and coupling the breaking circuit at the ends of the electrodes,and considering the meshes changes in the calculation process,the whole evolution process of the broken arc in the arc extinguishing system of a metal plate DC contactor is simulated.The whole dynamic arc evolution process is obtained through simulation,which includes the initial arc movement in the contact gap,the arc root moving from the contact to the arc inducing plate,the arc root moving along the arc inducing plate and the arc being cut into multi segment short arcs by the metal plate until extinguished.By analyzing the distribution field of temperature,airflow,current density,conductivity,density and air pressure,fundamental reasons of the cathode arc root transfer and the anode arc root stagnation and the striking behind the arc are obtained.By analyzing the relationship between the magnetic field distribution of external application and the force of the arc in the entrance area of the arc chamber and areas of metal plate,the influence of the magnetic field distribution on the arc root transfer is obtained.Under the existing simulation conditions,the effects of magnetic field distribution of different external application,different breaking speed and different metal plates structure on the whole evolution process of breaking arc are studied respectively.In order to verify the simulation results,an experimental platform was built and an experimental prototype was designed.A high-speed camera was used to record the arc images during the breaking process of the metal plate type DC contactor.The dynamic behavior characteristics of the breaking arc were recorded,and the influence of magnetic field distribution of different external application on the dynamic behavior of the arc was analyzed.The results of the experimental observation are compared with the simulation results under the corresponding conditions,and the results of the two are consistent.The study of this paper has a certain significance to improve the breaking capacity of the DC contactor and optimize the structure of the arc extinguishing chamber. |
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