Research On Power Supply System Modeling And DC Feeder Protection Of DC Railway Transit System

With the rapid development of China's urban economy, urban ground transportation has become increasingly tense, urban rail transit as the best choice to mitigate the traffic problems. However, the rapid development of urban rail transit has brought new problems for its safe and reliable operation of the power supply system: such as the train density increases when the peak of running, the suburban and intercity line power supply is excessively long, the early construction line gets older seriously and so on. Especially because DC feeder line laying conditions and poor running environment, which will more easily lead to short circuit fault under the influence of these new issues, a serious threat to the safe operation of urban rail transit. Therefore, the urban rail transit power supply system operating characteristics, failure analysis, protection and control technology and related issues on further research has the very vital significance.Through the analysis of urban rail transit power supply system working principle for its special power supply and run way modeling, analysis of operating characteristics and failure characteristics, study the configuration of the DC feeder protection and coordination, as well as new criteria and algorithms. The work mainly focuses on the following aspects:(1) Analysis of the special power supply mode and the locomotive operating characteristics of the urban rail transit power supply system, combined with the actual parameters and corresponding data obtained, this paper provides a comprehensive modeling and simulation of the power supply system traction substations, locomotives, rail and other major components, and the simulation results with the recorded data of metro DC feeder run were compared to verify the simulation model. Based on this, this paper puts forward the simulation modeling methods, including the locomotive over-segmented, short-circuit fault occurs when the locomotive regenerative braking, etc., studied and analyzed the operating characteristics and current characteristics of a variety of operating modes.(2) This paper takes a deep study on the significant effect of the skin effect on the variation of the DC feeder short-circuit current when the orbit through the short-circuit current generated by the skin effect. Derived and presented the rail equivalent transient current calculation method considering the skin effect, the method based on the strike voltage step series to obtain the current series response, and to realize the equivalent of cylindrical conductor rails current transient characteristics computing; as to the situation which short circuits in view of the far-end, through analysis power supply system short circuit return route model using the S-function module to achieve the above methods, uses this method and the orbital transition condition impedance computation mutual iteration realizes time the orbital far-end short circuits current transition condition computation.(3) Differentiating between remote short circuit DC feeder current and the locomotive constant torque DC feeder short-circuit current is the difficulty of the traditional protection algorithm. With the research of two current exponential function with characteristic time constant variation, a method based on Mexh mother wavelet has been presented for recognition of both current, taking full use of Mexh wavelet transform to extract the characteristics of the time constant of the exponential function ability. It uses reverse the large-scale wavelet transform to analysis DC feeder current and extract the time constant of variation to achieve recognition. DC feeder currents measured by a variety of different scenarios is transformed and analyzed to verify the proposed method effectiveness.(4) This paper proposed the DDL+wavelet rising rate program to protect the DC feeder protection, it takes full advantage of the superiority of the three principles of protection and make each other with the realization of a total length of100%of DC feeder protection:DDL+ΔI protection reaction with nearby short-circuit fault, the DDL+AT protection response reaction with middle-far distance short-circuit fault, the wavelet rising rate protection response reaction with remote short-circuit fault. It also researches protection parameter setting and cooperation, designs the protection implementation flow. With various simulation and on-site recording of data, the protection program was tested to verify the feasibility and effectiveness.