| In an electric railway,a train realizes electric energy transmission and drives forward through the contact line and the pantograph installed on the roof.In China,the power frequency of a 27.5 k V high-voltage single-phase AC power supply mode is widely used.The value of current ranges from hundreds of amps to thousands of amps on the contact line,which is depend on the slope of the line,train load,and other working conditions.The high voltage and large current on the contact line generate electric field,magnetic field,and electromagnetic pulses in the surrounding space.When the train is running,a pantograph–catenary（PC）arc is easy to be generated because the pantograph and contact line are separated instantaneously during several cases,such as,the irregularity of the line,the train is passing phase point,contact line icing,and sand dust pollution.When the train is stationary,it is also easy to generate PC arcs during the pantograph lifting and declining,which will produce the electromagnetic pulse radiation to the surrounding space.Existing research in this field mainly focuses on the electromagnetic compatibility of PC arcs,especially on the interference of the PC arcs to railway signal equipments,electrical damage mechanism and protection methods.Few studies discussed the dosimetry of the power frequency high voltage and large current of the contact line and PC electromagnetic pulses to passengers.Therefore,this dissertation presents the safety assessment of PC electromagnetic exposure and has important significance for dosimetry analysis in this area.The main research is as follows:（1）Safety assessment of occupational electromagnetic exposure to power frequency high voltage and large current on the contact line.In the COMSOL Multiphysics software,the electromagnetic models including a contact line with power frequency high voltage radiation source and a high signal operator are constructed.The electric field distribution in the body tissues of the operator are obtained for two cases,i.e.single-and double-line exposure sources.The results show that the exposure for the double-line is greater than that in the single-line with respect to the maximum electric field intensity in the body tissues of the operator.For the case of double-line,the maximum electric field intensities in the brain and body tissues of the operator are 0.19 m V/m and 310 m V/m,respectively.These values are0.19%and 38.75%of the occupational exposure limits formulated by the International Commission on Non-Ionizing Radiation Protection（ICNIRP）.Moreover,this dissertation constructs the electromagnetic models including a contact line with power frequency large current radiation source and a high signal operator.The electromagnetic field distribution in the body tissues of the operator are obtained for two cases,i.e.single-and double-line exposure sources.When two contact lines are working together,these values greater than in the case of one contact line.For a double-line case,the maximum values of magnetic flux density and electric field intensity in the central nervous system are 66.7μT and 0.9 m V/m,respectively.These values are 6.67%and 0.9%of the occupational electromagnetic exposure limit formulated by ICNIRP guidelines.The above results show that the power frequency high voltage and large current of contact lines have low safety risk on the occupational electromagnetic exposure of the high signal operator.（2）Safety assessment of occupational and public electromagnetic exposure to PC electromagnetic pulses.The distribution of specific absorption rate（SAR）and electric field intensity in the body tissues of a ground crew are calculated for the exposure case during the the train stops and the pantograph is lifting.The exposure levels for the ground crew at different positions are considered.The results show that the radiation intensity of the electromagnetic pulse decays rapidly with the increase in distance.For example,when the ground crew is far away from the center line of the track at approximately 3 m,the maximum SAR and electric field intensity in human tissues are 4.10μW/kg and 237 m V/m,respectively.These values are far less than thoese of the occupational electromagnetic exposure limit formulated by ICNIRP guidelines.This dissertation also studies the electromagnetic exposure level of passengers caused by PC electromagnetic pulses when the train is running.We have solved the distribution of SAR and electric field intensity in the body tissues of passengers at different positions in the carriage.The results show that the SAR and electric field intensity in the body tissues of the passenger near windows are considerably less than the public electromagnetic exposure limit formulated by ICNIRP guidelines.The aforementioned results show that the electromagnetic exposure caused by pantograph lifting,declining and PC arc pulses to ground crew and passenger is within the limit formulated by ICNIRP guidelines.（3）Experimental measurements for PC electromagnetic pulses radiation have been conducted for several cases,i.e.the train is running,the pantograph is lifting and declining.The measurement results show that the peak value of PC arcs during the pantograph rising is greater than that of the pantograph declining.The peak values of electric and magnetic field intensities for the pantograph lifting are 2.03×10-1 V/m and 5.37×10-4A/m,respectively.These values are 0.32%and 0.31%of the occupational electromagnetic exposure limit formulated by ICNIRP guidelines.This dissertation further performs experimental measurements for public expoure to the PC electromagnetic pulse along the railway line when the train is ruinning.The measurement results show that the maximum electric field intensities are 21.83 m V/m,18.13 m V/m,and7.90 m V/m at 10 m,20 m,and 30 m away from the line,respectively.These values are far less than thoese of the occupational electromagnetic exposure limit formulated by ICNIRP guidelines.The above research results show that the electromagnetic exposure levels of PC electromagnetic pulsses are within the limit of ICNIRP guidelines.The systematic research results of this dissertation indicate that the electromagnetic exposure level is within the limits for both of international and national electromagnetic exposure safety standards.The research results of this dissertation have important reference values for formulating the safety standard for the electromagnetic exposure of electrified railways,it also provide reference for designing the electrified railway and making safety protection for the electromagnetic exposure of the high signal operators,ground crew in locomotive servicing yard and passengers in carriages.In the mean time,this dissertation is helpful to eliminate the public and occupational concerns relating with the risk of PC electromagnetic exposure and its possible health risks. |
