Research On The Distribution Of Traction Backflow In Electrified Railways Based On The Theory Of Multiconductor Transmission Lines

With the development of electrified railways towards high-speed and heavy-duty,it has brought new challenges to existing line technology and equipment,and the problems caused by abnormal return current distribution in traction power supply systems cannot be ignored.Studying and analyzing the distribution and influencing factors of return current in traction power supply systems is of great significance for the safe and stable operation and development of traction power supply systems.Based on the above issues,this article conducts the following research:Firstly,in response to the complex issues of impedance extraction and related electrical parameter calculation in the traction network,based on the theory of multiconductor transmission lines,the construction methods of longitudinal series components and transverse parallel component models in the traction network chain network model were studied.Each component was equivalently coupled to form the mathematical model of the entire traction network chain network.The voltage between each conductor in the traction network was derived using the multi-conductor transmission line equation The relationship between current.At the same time,the calculation of internal impedance was completed based on different wire types;The impedance calculation of each conductor ground circuit in the traction network was carried out using the Carson Pollaczek formula.Taking the two railways of Han-Chang Railway and Shi-Tai High-Speed Railway as examples,the electrical parameters of the traction network of the direct power supply system and the Auto Transformer power supply system with back flow lines are analyzed and calculated.Secondly,for the analysis of traction return current distribution and other issues,the circuit model under direct supply mode is solved using the uniform transmission line theory to obtain the distribution of rail current and potential,and the solution formula for the return current of the traction substation grounding network in the direct supply system is derived.At the same time,in response to the complex structure of the traction network under the AT power supply mode and the difficulty in obtaining transmission line parameters,the constant current field theory is used to derive the potential formulas generated by the rail leakage current and the comprehensive ground wire leakage current in the ground,and then the solution formula for the return current of the traction substation grounding network in the AT power supply system is obtained.On this basis,CDEGS grounding analysis software was used to establish two traction return current simulation models for power supply modes based on the actual parameters of the Han-Chang Railway and Shi-Tai High-Speed Railway.The theoretical calculation results of the ground grid return current were compared with the simulation results,verifying the reliability of the simulation model.Analyze the effects of factors such as the distance between the locomotive and the traction substation,soil resistivity,and the number of conductors distributed in the substation grounding network on the distribution status of traction return current under different power supply methods.Finally,a comprehensive testing and analysis system for electrified railway traction reflux was designed and developed,using Lab VIEW software to achieve functions such as collecting,storing,and analyzing multi-channel current and voltage signals.Conduct on-site testing in multiple traction substations,analyze the test results,and obtain the distribution status of the traction substation’s return current.At the same time,the test results were compared with the simulation calculation results,verifying the accuracy of theoretical calculations and the reliability of the simulation model.