Research On Cable Traction Network For Electrical Railway

In China, the electrified railway is developing towards direction of long distance and high power. As the widely application of the Electric Multiple Unit (EMU), the neutral section becomes a restricting of the speed promoting of the EMU, meanwhile, the transient overvoltage happening when passing the neutral section becomes a threat of the safe operation of EMU. A novel cable traction network (CTN) is researched in this thesis. The power capability of the CTN is large and the cable traction power supply system (TPSS) is a fundamental solution of the negative and the neutral section in electrified railway.As a novel TPSS, the structure and voltage levels of the cable TPSS are different from the current TPSSs. There are two voltage levels existing in the CTN, meanwhile the capacitive effect of the cable will influence the electrical characteristics of the CTN. So it is important to research the electrical characteristics of the CTN. As the different structure and capacitive effect, the reliability and sensitivity of distance protection and current protection are reduced when adopted in CTN. So it is necessary to analyze the short circuit characteristic of the CTN and research a suitable protection scheme for CTN. The main contents of the thesis are as follows.(1) An equivalent model of the CTN considering the distributed capacitance effect of the cable system is proposed. The models convert the two-voltage level system into the same voltage level. And then the formulas of charging current and voltage raise at the end of the cable system are derived. The accurate simulations are proceeded to validate the accuracy of the proposed model.(2) The electrical characteristic of the CTN are analyzed based on the proposed equivalent model and power flow model, which consists of the current distribution law, the voltage raise at the end of the cable system, the equivalent impedance of the CTN and the power supply ability.1) The equivalent impedance of the CTN is gained.2) The cable length, the distribute separation distance and the system leakage reactance have positive correlation with the Franti-effect. And the compensation factor has a negative correlation with the Franti-effect.3) The power supply ability of the cable traction power supply mode is proved to be better in condition of the real line data and the actual load of Beijing-Shanghai High Speed Railway and the heavy load.(3) The cable section method is used to analyze the electrical characteristics of the grounding fault occurs in secondary winding midpoint grounding system. The short-circuit characteristic in different fault conditions are gained from the cable section method. And then the correctness of the method is verified in MATLAB/Simulink software. The formula of short circuit current is derived from the fault-phase cable analyzed method in unbalanced fault condition.(4) The low-voltage started current differential protection scheme is proposed taking advantage of the symmetry of the cable system. The scheme is judged by the line voltage, the transverse differential current and the differential current. At last, the effectiveness of the scheme is verified in MATLAB/Simulink software.