Design Of Stray Current Monitor System For The Urban Rail Transit System

In DC rail transit systems, the running rails are usually used as the return conductor for traction current. This arrangement mainly focuses on economic considerations, since it does not require the installation of an additional return conductor. 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 pipework 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, including those carrying oil, gas and water.This thesis analyzed the principles of the electrical corrosion and propose a module of stray current, from which we know what factors influent the generation of the stray current and how large proportion of each factor counts. Basis on those theories we used chip microcomputer to design a voltage collection module to monitor the polarized voltage of the stay current. Forther more, we also programmed a software use the PC to receive the data collected by the voltage collection module. The software can store the data into database automaticly. And the software can also analize the data which stored in the database to see the tendency of a special period of time of the polarized voltage coursed by the stray current. Then we know what to do to limit the umplitude of the stray current to minimize the influence of the stray current. I bet, the application of this system will relieve the hard work of the monitor of stray current and will save a lot of money.