Design Of On-line Detection System For Railway Signal Cable Fault

In the railway power cable system,the hidden dangers and risks caused by cable faults become more and more frequent with the large-scale laying of cables.However,offline detection methods which used currently cannot locate faults online quickly.Therefore,it is of urgent practical significance and application value to research an on-line detection system that can find cable faults efficiently and accurately.Based on the theory of Time Domain Reflectometry,this dissertation uses SSTDR technology to detect fault points and fault types,which can reduce labor costs effectively,detect hidden dangers in debug and ensure the safe operation of railway lines.Firstly,the dissertation introduces the traveling wave propagation theory of cable lines,the causes of railway signal cable faults and common fault location methods.Secondly,the time delay estimation algorithms get analyzed and compared,besides,the feasibility is verified through the Simulink.The simulation results show that the quadratic correlation time delay estimation algorithm has better peak sharpening effect,strong anti-interference performance and more accurate fault location for long-distance fault signals under low SNR.Then,the system scheme has been determined,and the hardware circuit and software program are designed,mainly including:the test signal generation module based on FPGA system,the collection of reflected signals,the signal conditioning module and the upper computer interface written by LabVIEW.Next,a prototype of the fault detection system is made,and the software and hardware of the system are debugged.The specific results are as follows:FPGA can send test signals and switch frequencies stably.The high-speed data acquisition card can process reflected signals reliably.The upper computer can provide a friendly man-machine interface which can carry out correlation operations through the data and display the results accurately.Finally,the prototype is used for the cable fault test while taking the actual railway signal cable as the test object,and the test contents include open circuit fault,short circuit fault and signal attenuation test.Through the analysis of the test results,it is obvious that each module equipment is operating normally,and the SSTDR method can realize accurate online measurement of cable faults for real.