The Research Of The Underground Stray Current Distribution And Automatic Drainage Current System

In the city subway and light rail transport system, generally using DC traction return running rails, therefore, it is inevitable that there will be current leaking into ground through the running rails, resulting in the electrochemical corrosion to the underground or surface metal components such as structural steel, underground pipe-lines and so on, and infecting its service life and safe operation. At present in China cities of Shenzhen, Changsha, Chongqing, Wuhan, Zhengzhou and other places are building subway, and application of the most advanced protective measures in the actual projects remain significant research direction.This paper describes the causes of stray current and the corrosion principles of metal structure underground in detail, concludes a variety of protective measures which can be adopted in practical projects in our country now. Analysis of the stray current distribution in the case of metro Industry generally using drainage current net, put forward the subway stray current calculation formulas without drainage current net and established the subway stray current analytical formulas considering the use of drainage current net. Bring forward the design ideas and design principles of the automatic drainage current cabinet, and analyzes monitoring matters and principles when using automatic drainage current cabinet in practice.The paper includes four main aspects。First, described the principles and harm of stray current, expanded the stray current disserving the metal, buried metal pipe-lines, concrete structures, passengers and locomotive personnel, communications, drainage current facilities and general principles, detailed of the stray current corro-sion of buried metal principles and analyzed the theory of the stray current breaking subway metal objects buried underground, and accordingly put forward a variety of stray current protection methods and measures; And than, established the analytical expression of the stray current distribution in the case of using the drainage current net in metro industry, by comparing the mathematical model both with the drainage current net and not, educed the stray current distribution difference in the condition of using drainage current net and no, and based on the analysis summarized in detail the general rules of stray current distribution, providing basis theory of taking protection measures for stray current. In the next, summarized and analyzed the emission current method when using the drainage current net, analysis of emission current status in case of fixed and variable current limiting resistor, and presents an automatic drainage current cabinet design in good drainage condition, making stray current protection achieve the best results. At last, analysis of Chongqing Metro Line No.6project im-plementation and the whole protective measures, providing a reference program for the project practical implementation.