Study On Operation Mode Of AC Power Supply System For Urban Rail Transit

The AC traction power supply system for urban rail transit consists of main substation and cable traction network.The system adopts power frequency single-phase AC system.It has no phase separation and can avoid the harm of stray current.It overcomes the shortcomings and inconveniences of DC and AC traction power supply systems,and provides a new and better choice for urban rail transit.Firstly,the operation mode of AC power supply system of urban rail transit is analyzed,and the power supply situation of substation under normal and abnormal operation is studied.According to the decoupling mode of traction substation,the most serious fault of urban rail transit line is found out.Secondly,the AC power supply system of urban rail transit is calculated in order to set up substations.The calculation of parameters of cable impedance matrix and admittance matrix,as well as the calculation of traction network impedance parameters and admittance parameters are explained.The cable and traction network models of AC power supply system in urban rail transit are given.Based on the established models,the calculation formulas of current distribution in cable traction network and the calculation formulas of current magnitude at the outlet of substation are derived.In view of the situation that the error of voltage loss calculation formula increases with the increase of locomotive power factor in recent years,the formula of line voltage loss suitable for locomotive power factor is derived,and the formulas of traction network and cable line voltage loss are derived respectively,and the correctness of the formula is verified by the simulation model.According to the abovementioned setting principles and related power supply calculation formulas,a practical design of No.18 urban rail line in a city is carried out.The maximum distance between two traction substations is calculated under the limitation of voltage loss.Thus,the traction substations of this line are arranged and the number of traction substations is set up.Then the current at the outlet of the substation is calculated and the capacity of the traction substation is set up.The same method is used to set the number and capacity of the main substation.After the design of the whole urban rail line is completed,the power supply capability of the whole urban rail line is simulated and verified by using Matlab/Simulink under three conditions: normal power supply,traction substation power supply and main substation power supply.This design can meet the relevant standards in three power supply situations.Finally,according to the reliability calculation,the cable standby mode of AC power supply system in urban rail transit is selected.The GO method analysis process and the related calculation formulas of series model and parallel model are introduced.Finally,the cable of traction power supply system in line 18 of urban rail transit is not standby,50% standby cable and 100% standby cable are available.Reliability calculation,through the calculation results and the impact of economy,it is suggested to choose 50% standby mode.