In order to study the interference range and influence degree of stray current in dc traction power supply system, Liu Wei, Yin Yichen, Pan Weiguo, Yang Long and Zhang Hao, researchers from the School of Electrical Engineering, Southwest Jiaotong University and Beijing Whole Road Communication Signal Research and Design Institute Group Co., LTD., wrote in the 23rd issue of “Transactions of Electrotechnical Society” in 2021.The distributed circuit of the backflow system was equivalent to the centralized circuit, and the centralized equivalent circuit of the traction power supply system was established. The power flow of the system was calculated by the node voltage method. Based on the results of the power flow calculation, the dynamic distribution model of the whole line stray current with time was established.The diffusion model of dynamic scattered current in layered media was established by superposition principle and solved by Prony method. Compared with the simulation results of CDEGS software, the calculation error of ground potential was less than 8.66%.In the dc traction power supply system of urban rail, the rail has distributed resistance to the ground, and part of the reflux current leaks to the ground and flows back to the negative pole of the rectifier unit near the traction station. This part of the current is called stray current.Stray current produces electrochemical corrosion on buried metal structures.In the actual operation process, multiple traction substations run side by side, and the moving loads of multiple trains change dynamically with time, which causes dynamic changes of rail potential and stray current along the whole line, and causes constant fluctuation of ground potential near the subway line, and also changes of corrosion of buried metal structures.In order to control the electrochemical corrosion of buried metal structures, it is necessary to determine the interference range and influence degree of stray current, and take corresponding prevention and control measures.The researchers from the School of Electrical Engineering, Southwest Jiaotong University and other units studied the influence range and degree of stray current on the underground environment near the subway line in the case of multiple sections and multiple trains, and deduced the dynamic distribution model of stray current between multiple trains and multiple zones with time.Considering the stratification of the medium, the superposition principle is used to establish the potential distribution model of stray current in the ground, and the dynamic characteristics of the ground potential gradient along the subway line are obtained.The accuracy of potential distribution model in layered media was verified by CDEGS simulation.The interference of stray current to underground environment is analyzed based on a practical engineering case, and the influence of transition resistance, longitudinal resistance, dielectric resistivity and calculation distance on ground potential gradient is discussed.Researchers point out that increasing the transition resistance of rail to the exhaust network is the most important measure to control the geopotential gradient along the DC traction power supply system.Keeping a long distance from the subway is the key to reduce the influence degree of stray current.In this analysis, 6B trains are used, the maximum speed is 80km/h, the departure interval is 2min, the concrete resistivity is 0.503 ω •km, and the soil resistivity is 38.9 ω •m. When the distance between the buried metal structure and the subway line is 50m, the rail transition resistance value increases to more than 40 ω •km.Or when the rail transition resistance value is 5.31 ω •km, the distance between the buried metal structure and the subway line increases to more than 0.25km, and any position of the whole line is less than 2.5mV/m.This paper is published in The 23rd issue of Electrotechnical Transactions in 2021. The title of the paper is “Diffusion Model of Dc Dynamic Stray Current in layered media”. The authors are Wei Liu, Yichen Yin et al.