Research On Short-Circuit Fault Of Metro DC Power Supply System

As China's rapid economic development and the acceleration of urbanization, for most of cities subway construction has become the best choice to ease traffic pressure and to reduce environmental pollution, and the best economic use of land. So the number of subway lines in major cities is increasing. Metro power supply system is one of the important electrical equipment in the subway system, which bears the subway trains and various auxiliary equipment supply task. Power system security is important for the safety of passengers, operations personnel safety, traffic safety, equipment safety and other aspects. Fault Analysis of DC system is not only the basis of power supply system equipment selection and protection setting, but also ensure the protection reliability, selectivity and sensitivity, which provides power supply system the essential security protection.In this paper, the structure of Metro power system was analysis, and power supply system was divided into the main substations, traction substations, traction network. Substation from the city grid to the main substations was equivalent into impedance, analyzes was focus on the traction substation and traction network as main infrastructure, to calculate the dc-side short-circuit current. First, based on the basic structure of a variety of traction transformer and rectifier, the widely used 24-pulse rectifier was analyzed under different load conditions. On this basis, the short circuit current calculation method of power supply system was analyzed. Then based on VC++/MFC and LU decomposition method, the development of the Metro power system short circuit calculation software was realized. With the comparison of the simulation results and the Shanghai Metro Line 3 the short circuit testing results, reliability of the software was verified.On the basis of the simulation, the analysis method of the short circuit current calculation was analyzed, and a simplified appropriate model for the Metro power system short circuit was established, which can provide the theoretical basis for system analysis and equipment selection.Meanwhile, in this paper the short-circuit failure analysis is based on the line protection means, such as high current trip protection, current incremental and rate protection, over current protection and so on. And a number of detailed analysis for the key issues of those protection methods were analyzed, such as the current rate, the maximum short circuit current, time constant, steady-state short-circuit current ext.