Research On The Key Technologies Of AF904 Track Circuit And The Design Of Fault Treatment Scheme

The appearance of audio frequency track circuit(AF904)realizes the dual-functions for train occupancy detection and sending vehicle digital coding cab signal to on-board equipment and improves line utilization effectively.This system is used in Shanghai Metro Line 2.According to the design,the shortest headway for Shanghai Metro Line 2 is 100”,which reflects the high efficiency of this system.This paper briefly reviews the current situation of the research on the domestic and foreign track circuits,then the thesis introduces indoor and outdoor devices and working principle of AF904 track circuit system,then it makes a brief analysis of the causes of the fault and the fault influence.The red light strip fault of AF904 track circuit mainly includes the influence of the switch system,the TWC system and the operation.The main causes include the interference of the traction backflow,the interference of the adjacent track section and the factors of the S bond.By using AF904 track circuit parameter model construction and the field data measurement at JINGAN TEMPLE station,it determines the rail transport properties-linear distribution,then studies the formula-the primary parameter and the secondary parameter and analyzes rail impedance,characteristic impedance and transmission constant by using MATLAB tools to get the modulus and phase information,at last,Open Short Circuit Two Voltage method is finally chosen to calculate the basic parameters of track circuit.Based on above theories and indoor and outdoor equivalent circuit research,it determines calculation formulas and standards for some important parameters,such as characteristic impedance,resonant frequency,quality factor and frequency character.These key technologies provide a theoretical basis for the processing of AF904 track circuit fault.In order to solve the interference of the power supply traction return factor to the track circuit,two design schemes are compared.Reducing signal loop along the rail and setting the double loop to be two metres can effectively reduce the traction current interference of track circuit;in order to solve the interference of the adjacent track section,the parameters of the two schemes are compared,reducing the tap coefficient and pulse width of the interference section at the sending end and reducing the tap coefficient of the fault section at the receiving end can effectively reduce the red light strip fault caused by the interference of the adjacent track circuit section.Through the comparison of the physical connection,electrical parameters,train positioning,passing bond dection time and pre shunting distance between single S bond and double S bond,using the double S bond to replace the existing single S bond,when the single S bond falls off the red light strip fault will not occur reaching the goal of the redundant structure of double S bond.