Modeling For DC Traction Power Supply System And Development Of Protection Algorithm Based On Discrimination Of Current Characteristic Quantity

Security and reliability of the DC railway system is very important for entire urban railway system. The power supply system is one of the most important parts of DC railway system, therefore, it is necessary to research and study on the modeling of DC railway power supply system in order to analyze system operation and fault conditionof DC railway system. This paper studied on the configuration and characteristics of DC railway power supply system. By development of models for various sub-systems of the DC railway system, this paper presented a comprehensive model of the whole system based on MATLAB/Simulink. Modeling work includes traction substation rectifier system; locomotive traction load system; metro vehicle electric drive system as well as the rail system. Traction calculation has been conducted based on the data of Beijing Metro Line 13; the results verified the accuracy of the modeling work.Because of the diversity of DC power supply system and frequent changes in electrical parameters while the locomotive is starting, accelerating, coasting, braking or regenerating. This paper developed different models and implemented thesimulation and test separately for different feeding arrangement and operation condition of DC power supply system, analyzed the characteristics of the typical train starting current and remote short-circuit current based on simulation results, summarized the difficulty of the discrimination between train starting state and short-circuit by traditional protection algorithm.Protection algorithm is core technology of DC railway protection system, based on the current rising rate protection and current increment protection, this paper proposed a new protection scheme based on discrimination of current characteristic quantity, investigated on the principle and setting value of the peotection scheme, and then designed the algorithm logic for protection scheme.The reliability of protection device is one of the key issues of DC protection system. This paper combined the Simulink simulation and MATLAB programming method, a comprehensive program has been developed for the DC railway protection scheme by MATLAB m language and tested test respectively by Simulink model which made for different scenarios of DC railway system. Testing results proved the effectiveness of the protection scheme. The accuracy and sensitivity of the algorithm have also been verified by the program.Because of the frequent changes of electrical parameters in DC traction system, the sampling rate of protection devices could affect the test result of protection algorithm directly. This paper presents a new MATLAB/Simulink automaticly testing program, which can repeat the test with different sampling intervals, so the operations and the final trip decisions of the protection could be analyzed with each sampling interval. Therefore the optimum sampling rate for the hardware platform of DC railway protection is demonstrated by the automaticly testing programThe simulation model presented in this paper coincide with the actual situation, the program made for protection algorithm based on discrimination of current characteristic quantity can effectively protect the whole feeder line. Simulation results of different test cases proved the effectiveness of this approach and the accuracy and sensitivity of the algorithm have also been verified by the program. The study of optimum sampling rate provides a theoretical basis and pre-experimental basis for the practical engineering applications and products design.