Study On Theory And Simulation For Fracture Rail Detection Based On Track Circuit Traveling Wave

In order to meet the requitments of maintenance and operation in some rail line segment,track circuit is not installed,which leads to the rail fracture is not easy to be found in time.For this reason,a serious traffic accident will be caused.Therefore,in order to operate train safely,it is one of the important measures to achieve rail fracture detection for above sections.When electromagnetic wave travels in the circuit and goes through fracture point,the reflection and scatter will happen because the transmission impedance of rail fracture point doesn’t match,which make signal changes in the circuit.According to this principle,a new method is put forward to realize fracture detection based on traveling wave.In order to achieve it,the key theory of the method is researched deeply.First of all,according to the equivalent circuit of track circuit,track circuit transmission line equation is established,and solved by the homotopy analysis method,the Laplace transform method and FFT in conjunction with Quotient-Difference(Q-D)algorithm.By comparing these methods,the FFT in conjunction with Q-D algorithm can get numerical solution of track circuit with complex operation in the time domain,and the precision is higher.By decoupling transformation of track circuit transmission line equation,the equivalent circuit is obtained to set up Electro-Magnetic Transient Program(EMTP)simulation model of track circuit.The time domain solution solved by theoretical analysis is correct,which is validated by EMTP simulation model.Secondly,the models of broken,crack and shunt operation of track circuit in the complex frequency domain are established.According to the three kinds of operation states of track circuit boundary conditions,the current and voltage traveling wave expression of three operation states in the complex domain are concluded under zero state response.The track circuit models of broken,crack and shunt operation are set up in the EMTP.The theoretical analysis of track circuit are proved correct by the simulation.As the rail broken or crack when the detection section is idle,according to basic principle that the whole response is the sum of zero state response with zero input response,the whole response during those three operations are analysed to achieve the rail fracture detection.As the rail broken or crack when the detection section is occupation,the fracture detection is achieved by combining the steady-state responses of normal operation with the steady-state responses of broken or crack operation.Thirdly,based on ZPW-2000 A frequency shift overlapping track circuit,ZP·W1-18 frequency shift overlapping track circuit,broken rail detection with communication based train control(CBTC)and the principle of detection broken rail using track return current,a new centre-fed double-side current-received detecting track circuit is presented.According to the mathematical modeling of the detecting track circuit have been established,the detecting track circuit is equivalent to single feeding and single receiving track circuit.The current traveling wave of receiving end of detecting track circuit are got under the two kinds of detection methods.Lastly,based on the principle that wavelet transform can detect signal singularity point,the sym8 wavelet is selected as wavelet function,and the wavelet transform modulus maxima of travelling wave signal under the two kinds of detection methods are extracted.The simulation show that wavelet transform modulus maxima can identify the rail fracture.Therefore,the method of rail fracture detection by analyzing the change of travelling wave signal is proved theoretically.