Standard EMU Vehicle Body Overvoltage Effect On Shaft End Speed Sensor

The operation of the high-speed railway relies mainly on electricity,and the EMU is equivalent to a high-power electrical equipment.EMU is fast moving during operation,and the working environment is changeable.The electromagnetic transient switching interval of the roof high-voltage traction power supply circuit is short,and the frequency of overvoltage is far higher than that of most electric equipment in the power system.Frequent overvoltage shocks are easy to pose a threat to the safety of on-board equipment and personnel.In the field operation,the on-board speed sensor frequently fails due to the surge and overvoltage impact of the vehicle body,so it is urgent to carry out detailed analysis and research on the cause of the speed sensor circuit chip burning.This article first introduces the commonly used traction power supply methods for high-speed railways and the standard EMU power supply main circuit,and then combines the survey data and field measurement parameters to simplify the modeling of the traction power supply system and the EMU circuit;Taking the transient opration of VCB as an example,a PSCAD simulation model of transient overvoltage of a standard EMU is established.The simulation results show that the simulation model is correct.Based on the simulation model,the influence law of the coupling capacitance between the arrestor,contact net and the roof on the high-voltage cable core and the vehicle body’s surge overvoltage is further analyzed.After the vehicle body surge overvoltage magutide and waveform of is verified,design experiments on the speed sensor shield double end grounding and single side under the two grounding ways,using impulse voltage generator to generate 1.2/50 of the 200 ～ 6000 V lightning impulse voltage applied on the sensor shielding layer,at the same time with the oscilloscope detection speed sensor wire electrical side outline of transient overvoltage peak value,the test results show that the single side grounding mode cable core of up to 600 V peak transient voltage,exceed speed sensor protection device voltage grade,easy to cause speed sensor circuit chip burned down.By analyzing the propagation path of the surge overvoltage of the vehicle body,combined with the structural design of the speed sensor and the impedance measurement parameters,a simplified overvoltage propagation PSCAD circuit model is established.The simulation results show that the conduction overvoltage of the core wire of the speed sensor is positively correlated with the value of the coupling capacitance between the shield layer and the core wire;it is negatively correlated with the value of the coupling capacitance between the cable core wire and the ground wire.Reduce the coupling capacitance between the shield layer and the core wire and increase the coupling capacitance between the core wire and the ground wire to enhance the ability of the speed sensor to resist the surge overvoltage interference of the vehicle body.