Study On The Grounding Return Current Distribution In The Process Of Passing The Boosting Cable Of High-speed EMU

With the rapid development of high-speed railway,the security problem also appears more and more important.The grounding system of EMU is not perfect at present,concentrated protective grounding can’t ensure the body potential is zero,scattered protective grounding have return current,the superior and inferior protective grounding method is related to the running performance of the EMU directly.The EMU in China adopts dispersive grounding system,which produces return current among grounding points and forms potential threat to the safe operation of the EMU.As the standard EMU in China has been researched and developed,the grounding system is very important.The problem of EMU grounding attracts wide attention from relevant enterprises and universities,while now there are no uniform standards over the world,therefore,intensive study the grounding system of EMU is great significant.The model of carriage of one kind high-speed EMU in china and the model of catenary based on the AT power supply mode have been built by Simulink simulation software in this article to simulate the grounding current distribution at the different place during the boosting cable interval,then some conclusion can be obtained by longitudinal comparison:When the train runs from left to right during the boosting cable interval,the change trend of two working grounding current at same transformer is opposite,and the range is 100-200A.The reason of working current variation is the rail impedance between two working grounding.The amplitude variation rule of protective grounding is that No.1 car increase and No.8 car decrease gradually,the change range between 0～150A.Near the central car,the amplitude is smaller.The phase variation rule can be summary:The phase of protective current is related to the position of the train,the holistic regularity is that the current flow into the car body from the protective grounding of far away from the boosting cable and flow out from the No.1 car and No.8 car,which near by the boosting cable.When the train pass the boosting cable,the grounding current amplitude that arrive the boosting cable reach maximum,then the current concentrated and flow out the carbody.The grounding current waveforms of field test could be utilized to analysis and verify the current distribution rules.It is found that the protective current amplitude and phase change periodiclly affected by the boosting cable,and the cycle is about 20s,which is the time required through a boosting cable interval.The amplitude and phase change rule of working current and protective current in accordance with the simulation results.The max amplitude of protective current is 170A when the No.1 and No.8 car arrive the boosting cable.In addition,the scheme that adding a grounding resistance of 0.5Ω to the grounding axle of No.1 and No.8 car,adding a 0.15Ω to the second axle of No.3 car and third axle of No.6 car,adding a 0.08 Ω to the third axle of No.3 car and second axle of No.6 car,No.4 and No.5 car without grounding resistance,can reduce all the protective grounding current amplitude and improve the evenness effectively.The above conclusions provide theoretical foundation for designing better grounding system.