| The power distribution system in the new rail traction is generally a DC power supply system,and its rated voltage and current are generally kilovolts and kiloamps.Among all kinds of the components used in the distribution system,DC high-power contactors are key components.In this application,the voltage and the current levels are relatively high,and the main load is inductive load with large time-constant.In order to be used in this application,the contactors must have great capability on arc extinguishing because 1)no current zero for breaking a DC load and the arc is difficult to be extinguished and 2)the inductive load with a large time-constant strengthened the difficulty.Also,high electrical life-span is also inevitable for the frequently break and make.For a long time,the core problem restricting the development of the contactor especially in China is the arc extinguishing ability and rapidity under the condition of high-power DC inductive load.Therefore,this paper was focused on the arc characteristics inside the arc chamber of a bridge-type contactor.A couple of simulations and experiments were carried out on studying the dynamic arcing process and the arc transfer process in the arc chamber.Firstly,a 2-D magneto-hydrodynamic(MHD)model on the arc chamber was built for a dc high-power contactor.The MHD model coupled the electrical field,the current density,the joule heat source,the thermal conservation equation,as well as the gas dynamic equations.In this model,factors including the electric circuit,the contact motion,the magnetic field provided by external permanent magnet as well as the metallic arc-splits were taken in to consideration.By solving the MHD model in a commercial software,we got the time evolutions of arc temperature contours,fluid velocity contours,current density contours in the arc chamber,we got the arc transfer behaviors and the arc-splitting process of the arc driven by both the external magnetic field and the gas pressure,we also got the waveforms of arc voltages and arc currents.Then,a dc high-power arc experiment platform with rated output capacity of1000V/1000 A is developed.This system uses a series of super capacitor modules to discharge and provide the high voltage and current output for arcing experiment.A PLC is used as the control core to realize the time sequence and protection logic of the breaking arc test for either a contactor or a simulated mechanism.A set of high-power resistors and inductors are used as the loadwhose time constant can be easily adjusted in the range of from 0 to 15 ms.On the basis of this arcing platform,experiment researches were carried out at different voltage and current level with different loads.Also,the validity of the MHD model for the arc chamber were also verified by the experimental result.Finally,based on the verified MHD model,arc behaviors were systematically studied.The influence of factors,including the number of arc splitters,the horizontal distance between arc splitter and the movable contact,the angle of the arc splitters,the vertical distance between arc splitter and the stationary contact as well as the magnetic flux density inside the arc chamber,on the arc characteristics were also revealed.This influence and results can be used to guide the optimization on the arc extinguishing capability of the arc chamber. |
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