| As one of the important distribution equipment,low voltage switchgear will inevitably produce arc during the process of breaking.The arc changes rapidly and dynamically in millisecond-level time,millimeter-level space,thus affecting electrical equipment breaking performance.The principle of generation and the law of development of the arc are hot spots and difficult point of common concern to the researchers both at home and abroad.Compared to the AC arc,because the DC arc does not exist phenomenon in the current natural zero crossing,so it breaking more difficult.It is a common technology to design the contact structure of contactor reasonably and make it produce magnetic field.It is an indisputable fact that the magnetic field acts on the arc to form magnetic blow.Therefore,it is of great significance to explore the influence of the external magnetic field and its variation on the DC arc and the beneficial arc extinction.In this paper,the mathematical model of external magnetic field and DC arc is established through the theory of electromagnetic field numerical calculation,providing guidance for the design of the structure of the external magnetic field device for DC contactor by numerical simulation.Comparing and simulating the magnetic field distribution of a variety of permanent magnetic materials,the results indicate that the arc model in 3D magnetic field calculation is different due to the difference in conductivity.This provides a theoretical support for the selection and design of a reasonable external magnetic field generator.A mathematical model of arc is established,which combines the characteristics of arc motion and mechanism of arc based on the theory of magnetohydrodynamic(MHD),simulate and analyze the arc characteristics and arc motion characteristics respectively under the action of external magnetic field to explore the common mechanism of different external magnetic field effect on DC arc,and studying on the essential law of motion characteristics of arc under external magnetic field.The control of arc by external magnetic field,this is to provide a theoretical basis for studying the arc characteristics and the motion behavior of the arc under different magnetic fields.In order to verify the correctness of the theoretical analysis and simulation calculation,the experimental platform of DC contactor arc breaking characteristics is established.The high-speed camera is used to collect and image the arc breaking process.According to the image of the experiment and the data of analysis,the arc morphology and the variation rule under different magnetic field are summarized,and combined with the simulation analysis results,studying the phenomenon of reverse motion when breaking the DC inductive load under the effect of external magnetic field,and the characteristics of arc,such as temperature,airflow field,stress and pressure etc.The results show that the external magnetic field of arc voltage was increased,the arc extinguishing time is reduced,the transverse magnetic field to arc;The effect of transverse magnetic field can shorten the random moving time of the arc,which is helpful to the arc root motion,to improve the arc root movement and to increase the arc offset;The effect of the radial magnetic field can decrease the arc temperature and conductivity,which leads to the increase of the equivalent resistance of the arc. |
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