Protection Scheme Research Of Cophase Power Supply System For High Speed Railway

Thanks to the use of balance convert devices, cophase power supply system can eliminate system imbalance, filter harmonic current and compensate reactive current, so the unsymmetrical single-phase load which usually have a sharp change, abundant harmonic and low power factor may be regarded as a pure resistance symmetrical three-phase load to the power system. There is no necessary for its primary phase-changing and the feeder voltage from substations is the same value. The electric neutral section can be removed and problems which arise from it can be solved fundamentally. As one part of cophase power supply system, protection scheme is always important. In the cophase system, current and voltage in traction power supply changed and the regular protection scheme is not adaptive to the system any longer. So configuring a good protection scheme using all kinds of modern science technology considering cophase system's characteristics plays a very important role in the high-speed and overloading railway transport's high efficiency and safe operation.In this thesis, firstly, through the analysis of the load current and fault current characteristics of cophase AT traction power supply system, a double-end (or multi power supply) feeding system with all-parallel AT is proposed. Its electrical energy loss and the voltage drop of power supply across regions under fault is compared in theory with the existing single-end feeding system with AT-parallel only in the section posts. Furthermore, the feeder protection and control scheme logic and flow of double-end (or multi power supply) feeding is discussed. The mutual transition between it and regular feeding system is studied.Secondly, the effect of heavy load input and feeder short circuit on balance convert device is analysised and preventive protection sheme of balance convert device is studied. They are simulated by the tools Matlab/Simulink. Later the effect of balance convert device which came out of action on the system power quality is presented and the balance convert performance detective protection scheme of balance convert device is proposed.Thirdly, the various feeder short circuit faults of double-end cophase feeding system with all-parallel AT are discussed in detail. Through the mathematical analysis, the impedance and current distribution of traction power supply network under various faults is founded. Then it is compared with all-parallel AT with single-end power supply and On the basis of this, considering other factors, a set of traction power supply network protection scheme is brought forward.