Research On The Unbalanced Traction Current Of The Traction Power Supply System

The interference caused by the traction power supply system on the railway signaling equipments mainly has three aspects:electro-static discharge interference, electromagnetic radiation and conductive interference. And the conductive interference caused by the unbalanced traction current is the main interference source of track circuit. Track circuit is used to detect whether the railway line is occupied, and also used to control the signal equipments and turn point device. When the unbalanced traction current is larger than a certain limit, the conductive interference can be received by the receiver of the track circuit, which can cause the misoperation of the track circuit and affect the safety of the train operation. Thus, it has certain directive significance to research on the unbalanced traction current of the traction power supply system, analyze its principle and predict its harassment effect to the track circuit for the construction and operation of the electrified railway.First of all, the development of the electrified railway is described. Then the component parts of the power supply system and the main power supply modes of the contact networks are introduced. Based on theoretical calculation and the derived method, the harmonic mechanism of the traction power supply system is analyzed, and the main harmonic sources are given. The basic principle of the track circuit and the generating mechanism of the unbalanced traction current on the track circuit are also introduced and analyzed. The test on the current harmonic content and amplitude is done, and then the testing results are analyzed with data fitting method. The variation tendency of the amplitude with the frequency is got. Besides, the harmonic current decay rates of forward and reverse traction cases are compared and analyzed.Secondly, ZPW-2000A frequency shift track circuit is researched in detail. Based on the theory of the four-port network, the mathematic model of the unbalanced traction current transferring on the track circuit is set up. The unbalanced current is injected from the middle of the model, which is different from the traditional model and is more consistent with the actual situation. The impedances of the receiving end in different frequencies are calculated. Then the harmonic component near the working frequencies of the shift frequency track circuit is researched in detail, and the attenuation of the harmonic current with different frequencies on the railway is given and the variation of the voltage and current at the receiving end with different frequencies is also given. So, it can be judged whether the receiver is disturbed according to the anti-disturbance threshold of the signal receiving equipment.The electromagnetic simulation model of the unbalanced current on the rails is established with the electromagnetic field simulation software. The innovation of the model is to use two linear current excitations to simulate the unbalanced traction current, and set different material parameters for the rails to simulate the imbalance of the impedance and the leakage conductance. With simulation, the corresponding current density distribution on the track can be got. The attenuation of the harmonic current with different frequencies on the railway is also got. The voltage value of the receiving end is obtained through the voltage monitoring function. The current value of the receiving end can also be obtained with the known impedance values. Then the simulation results are compared with the mathematical model.Finally, some conclusions are presented in view of the above analysis and some reasonable suggestions are also put forward.