Study On Simulation Internal Faults Model And Protection Principles Of The Scott Transformer With Secondary Midpoint Drawn-out

According to the "11th five-year plan", more than 5000km passenger transport lines with speed of 300 km per hours will be built. AT power supply system is used in the high-speed electric passenger transport lines. One kind of the traction transformer is Scott balanced transformer in the overseas and domestic. The study of new traction transformer is the hot topic in the domestic power transmission technology area. The Scott transformer with secondary midpoint drawn-out is improvement of the traditional Scott transformer which is one kind of three-phase to four-phase balanced transformer and has the merits of restraining the negative phase sequence current. It can omit the autotransformer in substation and decreases the space occupation when used in electric railway. So it has high practical value in the construction of high speed passenger transport line.As the load-center of the different voltage transformation in the power system, transformer directly affects running stabilization of the traction supply system. Because the transformer is important and has higher price, so it should be set corresponding protection. Recent year, the correct operation percentage of transformer protection is relatively lower than the line protection and generator protection. Based on the electromagnetic inductive theory, founds the internal fault simulation model of the traction transformer is very important for us to understand the transformer and corresponding protection configuration.The paper summarizes many kinds of transformer internal fault simulation methods, puts forward the computational method of transformer internal faults simulation model based on the magnetic circuit. It also gives the computational method of B-H loop, induction matrix, leakage induction matrix, instantaneous magnetic permeability, core loss, equivalent resistance and so on.The paper given the current and voltage relationship between primary and secondary side of the Scott transformer with secondary midpoint drawn-out. Based on the traditional Scoot transformer's theory and fundamental formula. It analyzed the relationship between the transformer's primary voltage to three-phase voltage from power system, and the relationship between the transformer's secondary current to load current. It Educes the transformer's primary current, secondary current and voltage. When the transformer happens every kind of internal faults.The paper bases on the differentially current protection and analyzes three kinds of different protection connection method. It also bases on the derived current relationship and gives the differential formulate and brake formulate of the three kinds of connection method. The paper finds that the third method is best by simulating the inrush current of these kinds of method, definite the characteristic of tow-stage and three-stage operation and obtains the setting rules and standard formulate. So it has the value of reference on the protection's study and disposition of the Scott transformer with secondary midpoint drawn-out.