Study On Equilibrium Current Under AC Traction Power Supply Penetration Mode Of Suburban Railway

With the accelerating process of urbanization in China,the spatial structure of large cities is also changing,and gradually evolves from single center to multi-center.As a passenger rail transit in the metropolitan area,suburban railway has become an effective way to solve the traffic demand between the central city and the peripheral new city.The suburban railway has the characteristics of both trunk railway and urban rail transit.In view of its transportation demand,with the help of the co-phase power supply technology developed by the trunk railway,the suburban railway can adopt AC through power supply,and the traction substation can adopt co-phase power supply technology,cancel the phase separation at the outlet of the substation,and use the compensation device to control the negative sequence;at the same time,bilateral power supply is implemented between two adjacent traction substations,and the electric phase separation link in the district is eliminated to improve the power supply capacity and power supply reliability of the traction power supply system.The necessary condition for the use of bilateral power supply mode is to reduce the equilibrium current to the allowable degree of the power system,so the research on the equilibrium current of the AC traction power supply through the city railway can provide theoretical support and design basis for the realization of the AC power supply through the suburban railwayIn this paper,the Thevenin theorem is first used to equivalent the external power supply of suburban railway and analyze the different through power supply modes of traction side.Three kinds of AC through power supply schemes of suburban railway are proposed.The corresponding mathematical model is established,the calculation model of equilibrium current is derived,and the corresponding simulation model is built in MATLAB / Simulink simulation software to verify the correctness of the mathematical model and the calculation formula of the equilibrium current of the AC transfixion power supply scheme of the suburban railway.Secondly,the short-circuit fault analysis is carried out on the system side and the traction side of the AC through-type power supply of the suburban railway.Taking a municipal line as an example,the short-circuit faults of buses at different positions and different voltage levels in the system are simulated and analyzed.According to the simulation results,the traditional relay protection scheme is improved,and the new relay protection scheme is configured to ensure the safety and stability of the operation of the through-type power supply of the suburban railway.Finally,a city line is taken as an example for simulation.The equilibrium current calculation simulation model and system power flow simulation model of the example are built in MATLAB/Simulink simulation software.The power flow distribution and equilibrium current under different operation modes of the system are simulated and calculated,and the correctness of the equilibrium current calculation model is verified.It is obtained that the influence of equilibrium current on the power flow distribution of the power grid in the AC through power supply system of the suburban railway is within the bearing range of the traction transformer and the line,that is,it will not affect the safe operation of the power grid in the steady state.At the same time,when the voltage difference and phase angle difference of the traction substation meet the requirements of the management regulations,the proportion of the equilibrium current in the closed loop line is small.When the AC through power supply is used in the suburban railway,the influence of the equilibrium current on the power system and the traction power supply system is small,and it is feasible,which provides a reference for the subsequent construction of the AC through power supply system of the suburban railway.