Study On Subway Stray Current In Urban Rail Transit

In DC rail transit systems, the running rails are usually used as the return conductor for traction current. The rails along the railway, which lie exposed on the ground, will easily cause larger stray current. When the train operates in heavy transportation of mass rail transit (MRT) systems, the current required by the train will be quite large up to several thousand amperes and the resistance of the running rail will be about several milliohms to tens of milliohms per kilometer. Therefore, a significant voltage drop on the running rail will be generated. This voltage drop will force parts of the current to leak from the rail and flow into pipe work in the earth or steel bars in a structure. Afterwards, the current leaves the pipe or steel bar and flows through the earth, back into the negative side of the traction substation. This current is known as the stray current or the leakage current. Stray current causes electrical corrosion not only to the structure and piping in MRT systems, but also to adjacent structures and underground piping, includes those carrying oil, gas and water.Stray current would be effected by many elements, which are high uncertain. At present, Metro's Stray Current Model mainly was constructed by resistance components. The distribution of stray current from track to earth can be solved effectively by this model, but the distribution of stray current under earth not included.The stray current model based on electric field was built after the features of stray current model based on resistance components has been discussed, for analyze the distribution of electric field cased by stray current under ground. Then the caustic current obtained by electric field. At last the corrosion on buried metal was used as a visual standard to evaluate the harm of the stray current.The major work includes four aspects:1) The stray current's corrosion mechanism and the harm have been discussed.2) The features of stray current model based on resistance components have been analyzed, and its overall trends of distribution also simulated.3) The stray current model based on electric field was built, according to above works. And an analytical expression of the model for computer simulation was deduced. 4) Uses an Object-Oriented Programming language (C++ version 7.1) to develop a stray current corrosion calculation tool for solve the expression which deduced by the stray current model based on electric field, and the effect cased by arguments of the model also have been analyzed in detail.