| High speed EMU is a core part of high-speed railway system,whose safe and stable operation plays a very important role.In recent years,with the increasing speed of high-speed trains in China,the traction current is gradually increasing,and the safety of EMU is seriously affected by the unreasonable setting of the car-rail reflux coupling system of EMU.Except mentioned above,the abnormal wear of grounding carbon brush,potentiometric uplift,the error of train sensor and even the burning of the train often occur.Therefore,in view of the features of the car-rail reflux coupling system of the EMU in China,it is urgent to fully deconstruct the system and explore its characteristics of internal and external factors.This paper systematically introduces the research status of the car-rail reflux coupling system at home and abroad for traditional electric locomotives and high speed EMUs.According to the characteristics of EMU car-rail reflux coupling system,in this paper,the theoretical analysis of the car-rail reflux coupling system of the EMU is carried out,and the simulation model of the car-rail reflux coupling system of the EMU is built by utilizing the PSPICE simulation software.The related parameters of the model are established on the reference to the actual measurement.Based on this model,the transient peak current and the train body-shaft end potential of 8 formation of directly grounding EMU are simulated and analyzed,and the rationality of the model is verified through field test.The basic characteristics of car-rail reflux coupling are as follows: The transient peak protecting grounding current and the potential of car body-axis-end are larger in the head and tail,and smaller in the middle car.When the train is running between two adjacent boosting cables,the flow direction of the whole train protecting grounding current mainly manifests that it flows into the car body from the grounding that far away the boosting cable and outflows from the grounding which is closed to the booting cable.In the process of running through the boosting cable,the current in the protecting grounding axle is reaching the maximum value in its changing cycle.With the different protecting grounding axles passing through the boosting cable,it will cause the change of the current flow direction.It mainly outflows from the axis of the booting cable,and flows into the car from the adjacent axis.On the basic of characteristics of the car-rail reflux coupling,this paper further studies the influence of external factors on the car-rail reflux coupling,and draws the following conclusions: The transient peak protecting grounding current and the car-body-shaft-end under the different formations and grounding modes are still larger in head and tail car and smaller in middle car.The protecting current amplitude of transient peak at each shaft-end of the 16 formation is 1.9 to 9.6 times of that of the 8 formation,and the amplitude of the shaft-end which is more closer to the middle of the train increases greater after the reconnection.The way of resistance grounding can suppress the transient peak current of shaft-end in 12% to 44%.However,the potential of car body-shaft end will increase significantly,and the transient potential of lifting pantograph will also be higher.The matching of car-rail reflux coupling on coastal lines is not as good as inland because the position of rail connecting is more seriously corroded in coastal area.While the contact resistance of these positions increases the rail potential uplift and the reflux is blocked.The transient peak protecting grounding current in the conditon of joint-power supply arm is not in accordance with the features that it is larger in head and tail train and smaller in middle car,furthermore,the current amplitude in the conditon of joint-arm is 1.75 to 28 times than that of in the conditon of non-joint-arm.It is shown that the amplitude increases greater when the axis-end is closer to the middle of the train,the multiple is bigger,and the amplitude of direct grounding axis-end is bigger than resistance earthing axis-end under the operation of joint-arm,the multiple becomes larger.The EMU's car-rail reflux coupling matching at noon is not as good as in the morning because soil resistivity is higher at noon than that of in the morning and the rail leakage resistance increases so that the rail potential is increased and the reflux is blocked.The above research provides the theoretical basis for the improvement of the car-rail reflux coupling system and the formulation of the car-rail reflux coupling standard of the EMU. |
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