Research On Grounding Current Of Trains

With the rapid development of China’s high-speed railway technology, the electrical and electronic technology associated with high-speed railway is developing rapidly, which leads to increasingly complex electromagnetic environment of EMU vehicles. Due to the diversity of the train grounding and onboard electrical equipment grounding, a kind of ground current is produced on the train body, whose source is unknown and distribution is complicated. It is difficult to analyze the current precisely by conventional method. It will not only cause the conducted interference, but also produces the radiated interference. Therefore, the study of ground current can contribute to the research of the EMU vehicle electromagnetic compatibility.In this paper, we mainly study the sources, distribution and characteristics of the ground current on train body through the theoretical analysis, simulation and experiment. Based on theoretical analysis, we suppose that the ground current mainly come from high voltage equipment, like pantograph, traction transformer and current transformer. Besides, the surge voltage generated by overvoltage can produce the ground current as well.First of all, I established the large cross-section continuous metal conductor model. Following conclusions are reached by simulation:the current value distributed symmetrically around the zonal center of the injection point changes from big to small. When the distance is far enough, the current is uniform distribution. The distribution in metal body mainly appears surface current. When the concentration effect disappears, there will be current spikes at the edge of the metal body. The influence of the proximity effect makes the current near the loop larger. Then, the ground current situations of different grounding method were simulated. When the system is single point grounding, the resulting current is smaller than the multipoint grounding. Finally, we set up the EMU model. The distribution of current on the body was simulated under the independent effect of pantograph.In order to verify the simulation results, the metal plate experiment is carried out. Then the bodywork overvoltage experiment and the bodywork ground current experiments have been done to verify the current source and current distribution characteristics on the body. And, through a field case fully showed the complexity of ground current interference, which provided a new thought for the research of EMC of the high-speed rail system.At the same time, according to the field conditions and the characteristics of ground current, we have designed a kind of surface current test system which is suitable for EMU body current test. The surface current test system was designed based on the magnetic field sensor chip HMC1022. The design is novel and its circuit structure is simple.