Study On The Characteristics Of Return Current Under Ac Power Supply System Of Urban Rail Transit

DC power supply mode is adopted in most of the urban rail transit.However,a series of problems,such as,the corrosion effect of stray current,DC deflection of transformer,extinction of DC circuit breaker and inadequate utilization of regenerative braking energy,affect the quality and the safety of power supply.Compared with the DC power supply mode,the AC power supply mode has the advantages of strong power supply ability and long power supply distance and the increasingly mature of cable power supply technology,which provide a new way for the development of traction power supply system of urban rail transit.Besides,compared with electrified railway,the spacing of urban rail station is smaller;the mode of locomotive operation organization and traction and braking characteristics have some differences.So,the traction return current of the urban rail system which adopts the AC power supply mode have certain particularity and affects the power supply quality and security.Therefore,it is of great significance to study the traction return current characteristics of urban rail.In this paper,based on Carson theory and Tylavsky theory,the electrical parameters of the traction network in the tunnel section are calculated and compared them with the actual measured values.It is found that the resistance parameters obtained from theoretical calculation are basically consistent with the measured values,and the impedance parameters obtained based on Tylavsky theory,compared with which based on Carson theory,is closer to the measured value.So,the Tylavsky theory is used to calculate the electrical parameters of traction mesh in the section of urban rail tunnel.Secondly,taking a domestic urban rail line adopted direct power supply with return wire as example,according to the design principles and schemes of the urban rail integrated grounding system,the grounding resistance value of each grounding pole in the integrated grounding system is calculated based on the CDEGS simulation platform.A simulation model of urban rail traction power supply system of direct power supply mode with return wire is constructed by using MATLAB/Simulink simulation platform.The step voltage in urban rail tunnel are calculated.The distribution of rail potential under different urban rail grounding mode,driving interval and operation mode is studied.The measures to reducing rail potential,containing reducing the spacing between the return wire and the rail and adding integrated grounding line,is put forward and the effectiveness of the above measures is verified.Finally,the new power supply scheme of using direct power supply mode with cable is researched and the corresponding simulation model of urban rail traction power supply system is established.Compared with the conventional power supply scheme,the simulation is proved that the cable power supply scheme can effectively prolong the power supply distance,improve the traction return current distribution and reduce the rail potential.It also meet the requirements of urban rail transit for safe and efficient operation and has high engineering application value.