Dynamic Simulation Of Rail Potential Considering Rail Frequency Characteristics In Dc Traction Power Supply

Rail potential is generally too high in DC traction power supply system,and rail potential simulation only considers rail DC resistance model.However,the irregular section of rail and its ferromagnetic characteristics lead to the change of rail AC internal impedance with the change of frequency,which will have a great impact on the simulation results of rail potential,so it is necessary to build a dynamic simulation model of rail potential considering the frequency characteristics of rail.In the calculation process of rail internal impedance considering frequency characteristics,the irregular section of rail and its ferromagnetic characteristics will greatly increase the difficulty of calculation.Firstly,this paper compares and analyzes the advantages and disadvantages of the existing calculation methods of rail AC internal impedance considering frequency characteristics,and chooses to use the tubular conductor model to calculate the rail AC internal impedance at different frequencies.Then,the technical points of foreign rail frequency characteristic measurement platform are summarized,and the rail impedance frequency characteristic measurement platform is built in the laboratory.According to the measured results of rail AC internal impedance at different frequencies,the parameters of P60 rail equivalent tubular conductor are determined by fitting.In the actual operation line,the rail current contains a large number of 1 ～ 50 Hz and part of 6 times harmonic components.Based on the infinite earth model around tylavsky,the mutual impedance and admittance parameters of conductors at different frequencies are calculated,and the electrical parameters of the return system are obtained by electrical decoupling of the return system.A rail potential calculation method considering the equivalent tubular conductor model of rail and the AC component of the measured rail current is proposed under the complex working conditions of multiple traction substations and multiple vehicles.The reliability of the calculation method is proved by the example of unilateral power supply.By comparing the harmonic components of rail current and rail potential,it is found that the rail current injected by metro train contains abundant 1 ～ 50 Hz component and part of 6 times frequency component,which is more affected by 6 times frequency component in rail potential component due to the effect of rail impedance frequency characteristics.Although the calculation results of the above process are accurate,the method is based on the known actual rail current data.In this paper,the dynamic simulation system of rail return system based on foster circuit is built on MATLAB / Simulink platform,and the models including train,rail based on foster circuit and over voltage protect device arc are established respectively.In this paper,the rail potential under complex working conditions of multi vehicle,multi traction substation and depot ovpd reversion are simulated and calculated,and the correctness of the above dynamic simulation model is verified by comparing with the measured data.By comparing the rail potential simulated by different models,it can be seen that the rail equivalent to DC resistance will lose the high-frequency harmonic component of rail potential,which will reduce the maximum value of rail potential by 13.482%;equivalent to first-order RL circuit will increase the AC component of rail potential;equivalent to eighthorder foster circuit can effectively reduce the simulation error of rail potential.Finally,according to the simulation results,the causes of abnormal rail potential under complex working conditions of multiple traction substations and over voltage protect device reset working conditions are analyzed,and the corresponding improvement measures are proposed.