Study On Distribution And On-Line Monitoring For Subway Stray Current

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 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.The major work includes three aspects:(1) By derivating the mathematical model of metro subway stray current and its simulation, we know the distribution of the Stray current and the factors that influent the generation of the stray current.(2) This thesis also analysises the Stray current corrosion mechanism and the harm, determines the risk indicators and judgment of the corrosion of subway metal structures(3) Based on the monitoringof line 3 of ShenZhen Subway, a set of stray current Online monitoring system is designed.The system can collect the steel polarization potential and the running rails on structural steel potentials accuratural and reliable, and transmists the data to data communication controller. The data communication controller communicate the acquisition module, read the data real-time, process the data and transmist it to the background monitoring computer. The PC Kingview monitoring system can monitor the whole system monitor order remotely, collect,process and analysis the data, the system can eflect the monitoring information by statement and curve, provide reference for the protection of metro stray current.