Stray current automatic monitoring system and intelligent obviating current device in metro

Generally, the running rails in metro are used as the return circuit for traction supply current. As the lower insulation resistance of rail-to-earth, the traction current returning along the running rails will leak partially to earth before returning to the negative terminal of the DC rectifier. Such leakage current is called stray current. The stray current will affect the rail transit system itself and buried metal structure by causing corrosion, and influence the transit system lifetime and safety. It is highly necessary to realize automatic monitoring of stray current. In this paper, the calculating formulae of metro stray current are given out, a stray current automatic monitoring system based on the industrial Ethernet is developed and introduced. The stray current can be limited in a number of ways, installing obviating current device in metro is one of the most effective methods. A new type of intelligent obviating current device is presented.