| Metro stray current refers to traction current which leaks into the ground from rail in subway DC traction power supply system. In the ground, the stray current will flow into the surrounding pipeline system and steel structures and this will lead to their electrochemical corrosion. In the metro stray current protection work, measuring the magnitude of the stray current is meaningful and important. Accurate and detailed data can provide strong support for the stray current governance. A set of metro stray current online monitoring system was designed and produced in this thesis.Firstly, the research status at home and abroad and related standards of stray current were summarized. Then, the corrosion principle, the danger and the general law of distribution of metro stray current were analyzed. Besides the above, the detection principle and methods were summarized. Due to the special feature of metro stray current, it was monitored by an indirect way. The magnitude of the stray current is reflected by polarization potential of structural steels and rail potential.Based on the comparison of typical metro stray current monitoring system, distributed monitoring based on intelligent sensors was chosen as the monitoring way of this article. The design of intelligent sensor was introduced from hardware and software. The intelligent sensor based on LPC1758 was a small data acquisition device which was installed on both sides of the track. The device communicated with the host computer by the "103 agreement" of digital substation. When the device received the data-calling packets, it will upload the telemetering data to the monitoring computer.Then, the design of the monitoring software was described. The software was a data management software which run on a touch tablet computer. On the one hand, the software sent data-calling packets periodically, and after receiving the response packet, it will parse out the data and display on the corresponding interface. On the other hand, the software will put the data into the database. The operators can query historical data in the software and plot corresponding waves.At the end of the thesis, the relay protection tester was used to simulate input voltage. Also, the mainly functions of the system were tested. The result showed that the system designed in the paper could accomplish the monitoring work of metro stray current well. |
