Research On Electromagnetic Interference To Speed Sensor By Operating Overvoltage Of EMU

During the operation of the EMU,the main circuit breaker in the high voltage system needs to be closing and opening frequently,such as passing neutral section device,rising pantograph and other conditions.The circuit structure of the side of the EMU is changed,and the transient overvoltage is generated in the side high voltage system of the EMU,which will enter the train’s body through the distribution parameters of the high voltage equipment and leads to the violent oscillation of the train’s body potential.Because the cable of the speed sensor is shielded and grounded,the overvoltage of the train’s body is directly loaded on the cable of the speed sensor.On the one hand,it may cause the insulation breakdown of the speed sensor,or even burn down.On the other hand,the distribution parameters of the cable of the speed sensor are coupled into the core wire,which interferes with the speed signal and leads to speed misjudgment.So it is necessary to carry out the circuit breaker operating overvoltage of electromagnetic interference of speed sensor research,clarify the breaker operating overvoltage for speed sensor mechanism of electromagnetic interference,established from the interference sources-coupling path-sensitive equipment electromagnetic interference model,analysis of speed sensor electromagnetic interference caused by transient overvoltage.At the same time,in order to reduce the electromagnetic interference of the speed sensor,which is a typical on-board sensitive equipment,the research on overvoltage suppression technology for EMU operation is carried out,and the influence law of the train’s body protective grounding on the operating overvoltage is obtained,which provides a technical reference for the design of the grounding system of a new generation of trains.To studying the electromagnetic interference of operating overvoltage to speed sensor,this thesis first expounds the EMU speed sensor type,working principle and shielding grounding method,and then based on the principle of electromagnetic compatibility,analyzes the generating mechanism of overvoltage and disturbance mechanism of speed sensor.According to the EMU electrical structure,speed sensor electromagnetic interference model is established,including high pressure system module,grounding system module and the speed sensor module.For the first time the complete polygon impedance circuit is adopted to the train’s body three-dimensional and structures more accurate equivalent circuit,then the circuit breaker operating conditions interference sources,the overvoltage of train’s body and speed sensor simulation results are obtained.At the same time,by carrying out the overvoltage test study of EMU body under the circuit breaker operating condition,the test waveform of overvoltage of train’s body is obtained and compared with the simulation results in time domain and frequency domain,thus verifying the accuracy of the EMI model of the EMU speed sensor.In order to suppress the electromagnetic interference of operating overvoltage to speed sensor,overvoltage suppression technology for EMU operation is studied.A large number of studies have shown that the level of the operating overvoltage has a great relationship with the train’s body protection grounding mode.By improving the train’s body protection grounding layout,the train’s body overvoltage can be greatly reduced under the circuit breaker operating conditions,and the safety and reliability of on-board equipment such as the speed sensor can be improved.This thesis mainly makes a detailed analysis of the current body-grounding technology,including the categories of body-grounding and domestic various types of EMU body-grounding methods.On this basis for a certain type of EMU,analysis of factors influencing operation overvoltage are carried out,and the the train’s body overvoltage influence law of the train’s body grounding impedance,the grounding resistor distribution and the ground point distribution are obtained.some corresponding proposals are put forward on the improvement and optimization of the train’s body grounding technology,which provides reference for the unification and improvement of relevant standards of grounding technology on high-speed EMU.