Study On Optical Fiber Sensor For Monitoring The Metro Stray Current

The leakage stray current can corrode underground metal seriously in the metro DCpower supply system. Therefore，the stray current corrosion monitoring must be taken intoconsideration in the process of subway operation. In this paper, in view of the fact thatthere are some problems with the half cell potential method which is widely applied, suchas accuracy instability and IR drop. The metro stray current sensing system based onoptical fiber sensing technology is proposed to avoid the above problem.Firstly, optical system model of fiber optic current sensor and magnetic fielddistribution model of carrying current toroid are established respectively, and then outputmodel of fiber optic current sensor can be derived. At the same time, error factors influenceon the optical fiber current sensor are simulated using the Matlab soft, such as polarizerextinction ratio, polarizer axis angle and birefringent of optical fiber sensing head.Secondly, optical devices of the optical system are designed and selected, and then theoptical system of optical fiber current sensor is built; the signal detection and signalprocessing circuits are devised. Moreover, a prototype of metro stray current fiber opticsensor is developed. PC software design is accomplished by using LabVIEW software,which can achieve human-computer interaction, real-time monitoring, data storage andquery, user management and so on.Finally, the basic functional verification and performance test experiments are carriedout on the fiber stray current sensor by the developed prototype. Static characteristics andtransient response of fiber optic current sensor are analyzed according to the experimentalresults of the performance test.The experimental results show that the correlationcoefficient of fiber optic current sensor is0.9984, which has good nonlinear error; therepeatability error is0.38%; the relative error is within the range of1%though8hoursstability test; Minimum current value fiber optic current sensor can distinguish is0.01A.Furthermore, the current sensor has good transient response ability.