Analysis Of Transient Response Of Jointless Track Circuit Based On Multi-conductor Transmission Line Theory

ZPW-2000 jointless track circuit is mainly used to transmit train control information,traction return and check track occupation.It is an important signal equipment to ensure safe and efficient operation of trains and improve line passing capacity.With the increasing complexity of high-speed railway construction and operation environment,the frequency of signal system suffering from external electromagnetic interference increases.The transient electromagnetic interference signal will take the multi-conductor transmission lines system of traction network as the transmission line medium,which result in conduction interference or radiation coupling interference on the track circuit.Therefore,AT traction power supply system has also become an integral part of the research on the transient response of track circuit.To accurately analyze the transient response of the track circuit,the influence of non-linear load tuning area connected at both ends of rail and multi-conductor transmission lines system composed of traction network and track circuit on the overvoltage at the receiving end of incoming track circuit must be considered.It is significant to ensure the accurate transmission of track circuit signals.Firstly,the structure of ZPW-2000 A jointless track circuit and the calculation method of conductor space position and electrical parameters of at traction power supply system are introduced in this paper.When the lumped parameter model is used to study the transient response of track circuit,it is impossible to clearly analyze the variation law of current and voltage at any position.Based on the multi-conductor transmission lines theory and the spatial position structure of each line of traction network and the structure of track circuit,the theoretical calculation model of MTLS system of traction network and track circuit is established.Secondly,there are nonlinear lumped element circuits such as tuning region in the track circuit,so the transmission line equation cannot be derived directly,and the MTLs equation cannot be discretized by the finite difference time domain method.Therefore,the method of combining Thevenin with state variables is proposed to solve the voltage and current equation of the connecting node of the tuning unit.Combined with the transmission line equation,the calculation formula of the multi conductor transmission lines model of track circuit is obtained.The model is built in ATP-EMTP software for analysis to verify the correctness of the proposed method.Then,the frequency loss in the track circuit and the terminal frequency load are considered.The frequency convolution of the transmission line is obtained by Laplace transform of the frequency domain equation of the transmission line,and the discrete calculation is carried out by FDTD.The vector matching method is used to reasonably fit the impedance of the tuning area,and the piecewise convolution integral is introduced to deduce the voltage current relationship at the node of the tuning unit.The formula for calculating the overvoltage at the receiving end of the track circuit is obtained by combining the transmission line equation with the current equation in the tuning region.The state variable method is used to verify the method.Finally,according to the time-domain equation of multi conductor transmission line of track circuit,the influence of conducted interference and coupling interference between traction network lines on overvoltage at the receiving end of track circuit is analyzed,the attenuation ratio and propagation speed of transient signal on track circuit are obtained.The influence of track bed resistance,signal frequency,geoelectric conductivity and dielectric constant on transient response of track circuit is analyzed.It provides model and theoretical reference for track circuit design and anti-interference analysis.