Study On Issues Related To Stray Current And Rail Potential On DC Traction Power Supply System

These years, in order to alleviate traffic jams, improve the daily travel structure, guide andsupport the development of new towns, more and more cities develop urban rail transit (URT)energetically. DC1500V or DC750V is used in most of the URT traction power supplysystem of our country. The currents from this system return back through running rail. Sincethe isolation between rail and ground is imperfect, some leakage current from rail to groundoccurs. It generates a voltage between rail and ground, and may damage to the safety ofpassengers and maintenance personnel. The currents from this system returning back throughrunning rail, then there may be a great deal of stray currents corroding structural reinforcingbars underground. Many buried metal pipes, such as gas pipes and water pipes would bedestroyed when the stray currents leaked more seriously, and personal safety would bethreatened. The study of stray current and rail potential possesses great practical significance.Combine with characteristic of Guangzhou metro, this paper analyzes the principle,harmfulness, distribution and influence factors of stray current and rail potential, statistics themonitoring data.and puts forward some improved schemes about stray current protection andrail potential limiting. The main research contents are outlined as following:(1) Analyze the reason of causing stray current and rail potential as well as the harm byusing the basic principles of metal electrochemical corrosion and elements of DC tractionpower supply system. It points out that stray current could corrode structural reinforcing barsand metal pips underground and the high rail potential may hurt people even make the DCcircuit breaker trip in error.(2) It is concluded that the main influence factors of stray current and rail potential aretractive current, power supply distance, rail resistance, and the contact resistance betweenrails. and the land by presenting a mathematical model. Analyze the different distribution ofrail potential in condition of one and two trains running, and points out the distributivecharacters in different sections.(3) Analyze the basic elements of stray current and rail potential monitoring systems.Through the monitoring data, it shows that the situation of stray current leakage can accordwith the design code but there are some differences between the theory and practice on railpotential.(4) Research schemes about stray current protection and rail potential limiting. Summarizethe conventional preventing and controlling methods, especially analyze components andcharacters of the collection network. Then according to Guangzhou Metro project, the article puts forward effective schemes about stray current protection in design, construction andoperation, including insulation strengthen, return currents increasing and equipmentsimproved.