Study On Safety Evaluation Of Low-frequency Electromagnetic Exposure For High-speed Train Passengers

China's high-speed Railway has made brilliant achievements that attract worldwide attention.With the implementation of the Belt and Road Initiative,China's high-speed Railway will bring more benefits to the countries along the route.The successful experiment of a new type of Chinese maglev train shows that the “super high-speed rail” with a speed of more than 1,000 kilometers per hour will bring disruptive changes to people's travel modes.Studying electromagnetic radiation impact on passenger health which generated by high-speed trains is an unavoidable research topic in the future development of high-speed rail in China.In order to evaluate the safety of passenger's health at low frequency electromagnetic environment effectively,the affecting factors of the passengers' health must be analyzed.The continuous increase in the speed of high-speed-trains will inevitably requires more traction power and traction current,which is an important factor that leads to hostile electromagnetic environment in the electric multiple units(EMUs).In addition,the traction electrical equipment,high-voltage cables,and signal cables,etc.are all placed in a narrow space at the bottom of the cabin.The fact is passengers are very closed to the radiation source which is one of the factors that affect the health of the passengers.Therefore,this research needs to be resolved urgently.The research results would provide necessary data support for the electromagnetic protection of high-speed railway and eliminate the public panic from the electromagnetic environment in the carriage.The first chapter of this doctor dissertation elaborates the necessity of research on the safety of low-frequency electromagnetic exposure of high-speed trains,and the literature review of electromagnetic exposure research at home and abroad.On this basis,extract the main research contents and search significance..The second chapter provides a brief introduction of high-speed EMUs traction power supply system,the power supply principle of EMUs,electromagnetic disturbance source,coupling path,and analyze the main factors affecting the electromagnetic environment in high-speed train,and discuss the guidelines for mainstream electromagnetic exposure limits adopted in various countries.The main mechanism of the interaction between the low frequency electric field,the magnetic field and the human body and the principle of the corresponding electromagnetic field are analyzed.The finite element software COMSOL Multiphysics is introduced.In the third chapter,dielectric properties of biological tissues are studied.It is well known that the dielectric parameters(conductivity and dielectric constant)of biological tissues are the important basic data for analyzing the interaction between human body and electromagnetic energy.In this chapter,we first review the development of bio-electromagnetics,followed by the analysis of the dispersion mechanism of the four dispersion regions of white matter and gray matter,and finally analyzed the ? dispersion of muscle tissue.The results of this chapter on the dispersive mechanism of different biological tissues will provide an important basis for the development of fields such as electromagnetic dosimetry,clinical tumor organization,and impedance tomography.In the fourth chapter,taking two sets of power cables as radiation resources,firstly,the electromagnetic radiation of the passengers' heads and trunks are discussed by the low-frequency electric and magnetic fields generated by them respectively.All these data are far below the recommended values of public electromagnetic exposure by the International Commission on Non-ionizing Radiation Protection(ICNIRP),which indicates the electromagnetic exposure caused by power cables will not threat passengers' health.In the fifth chapter,the electromagnetic radiation generated by the contact line to passengers are discussed,and the complex electromagnetic radiation generated by the contact line and power cables are discussed.And all data are far below the recommended values of public electromagnetic exposure by the International Commission on Non-ionizing Radiation Protection(ICNIRP),which indicates the electromagnetic exposure caused by contact line and power cables will not threat passengers' health.In sixth chapter,the low-frequency electromagnetic environment of the carriage in the EMUs and general-speed trains are measured.The COMSIL Multiphysics software are used to simulate the distribution of low-frequency electromagnetic fields in the carriage,and comparing the measurement data with simulation data,it demonstrate that using finite element software to analyze the low-frequency electromagnetic radiation generated by contact network contact wires and power cables is accurate for passenger safety research.The main innovations of this dissertation are as follows:(1)On the basis of summarizing the literature on the biological spectrum of biological tissues,it propose for the first time that the increment mutation of relative permittivity can be used as the basis for determining the occurrence of biological tissue dispersion.Based on this basis,the starting and ending frequency points of four dispersions of the brain white matter and gray matter are determined.The Cole-Cole circle is used to analyze the dominate dispersion and the correspond polarization mechanism in the dispersion transition zones in white matter and gray matter.(2)The 3D electromagnetic model is built in the finite element software COMSOL Multiphysics,which including the radiation source,the real human body,and the real carriage.By means of an electromagnetic dosimetry method,the contact line,the power cable,and the different positions in the vehicle compartment are respectively analyzed.Electromagnetic dosimetry method is used to analyze the distribution of induction electromagnetic field of passengers' heads and trunks at different positions and in different postures when contact wires,power cables,and both were used together.The calculation results show that the passengers are safe in low-fequency electromagnetic environment.(3)Based on the above simulation model,the dissertation also compare and analyze the distribution of induced electromagnetic fields in the human body that exposed to the contact network when the shielded electromagnetic energy protection is provided with/without EMU train body.Research shows that the aluminum alloy train body can shield the power frequency electric field and the power frequency magnetic field.(4)This dissertation measure the low-frequency electromagnetic environment in the CRH5 EMU compartment.The electromagnetic environment in the EMU trains is simulated by COMSOL Multiphysics software.Comparing the simulated data with the measured data,the result of using electromagnetic dosimetry to study low-frequency electromagnetic exposure in high-speed train compartments is consistent and reliable.