Development Of High Precision Railway Signal Cable Ground Fault Location System

The railway is the main artery of national transportation,with increasing mileage in operation and increasing electrification rate.The railway signal cable transmits control,monitoring information and electric energy between the signal equipment and the control device,and is an important part of the railway signal system.Once a fault occurs,the traffic efficiency will be affected,and the traffic safety will be endangered.The most common fault in railway signal cable is ground fault.In order to be stable and safe,railway signal cable is either buried deep underground or placed in cable trough covered with heavy cement board.At the same time,the length of railway signal cable is long.In order to quickly deal with railway signal cable fault,it is necessary to accurately locate the fault location.The research on cable fault location mainly focuses on electric power,railway,aviation,photovoltaic and other fields.At present,in addition to the use of multimeter and megger,on-site workers also use instruments using the bridge method and the low-voltage pulse reflection method to locate faults in railway signal cable.In this paper,the traditional bridge method is improved according to the characteristics of the railway signal cable which have metal grounded sheath in the electrified section,and the automatic high-precision location of the ground fault of the railway signal cable is realized.The main work of this paper is as follows:(1)The traditional bridge method is improved,and the principle of the improved DC bridge method is introduced.According to the principle,the corresponding hardware is designed,the hardware summary structure block diagram is given,and each hardware module is introduced.According to the principle and hardware,a matching algorithm is designed,and the parameters of the algorithm are determined through experiments.In the simulation experiment of the improved DC bridge method,the average value of the absolute value of the positioning error is 0.236%,and the average positioning error of the 100-point data of the 100-meter railway signal cable physical experiment is 0.493 meters.When the ground fault is close to the test terminal,the positioning error is very large,and the change of grounding resistance has almost no effect on the positioning error of the system.(2)In order to deal with the interference brought by the complex electromagnetic environment on site,an AC bridge analog lock-in amplification method is proposed based on the improvement of the improved DC bridge method.The principle of the AC bridge analog lock-in amplification method is introduced,the corresponding hardware is designed according to the principle,the hardware summary structure block diagram is given,and the new hardware modules are introduced.According to the principle and hardware,a matching algorithm is designed,and the parameters of the algorithm are determined through experiments.The average value of the absolute value of the positioning error of the AC bridge simulation lock-in amplification method system simulation experiment is 0.309%,and the average positioning error of the 90-point data of the 100-meter railway signal cable physical experiment is 0.143 meters.When the ground fault is closer to the test terminal,the positioning error is slightly larger,and the change of grounding resistance has little effect on the positioning error of the system.(3)In order to reduce the cost and improve the flexibility of the system,an AC bridge digital lock-in amplification method is proposed based on the AC bridge analog lock-in amplification method.The principle of AC bridge digital phase-locked amplification method is introduced,the corresponding hardware is designed according to the principle,the hardware summary structure block diagram is given,and the low-pass filter module and the key points of hardware design are introduced.According to the principle and hardware,a matching algorithm is designed,and the parameters of the algorithm are determined through experiments.The average value of the absolute value of the positioning error of the AC bridge digital lock-in amplification method system simulation experiment is 0.293%,and the average positioning error of the100-point data of the 100-meter railway signal cable physical experiment is 0.128 meters.When the ground fault is closer to the test terminal,the positioning error is larger,and the change of grounding resistance has little effect on the positioning error of the system.