Study On A New Balance Wiring Scheme For At Power Supply

In our country, To satisfy the running of locomotive with high speed and high power, the auto-transformer power supply mode is mainly adopted in tractive power supply system of high speed railway traction. Considering the features of electric railway, if the traction transformer adopt unbalanced connection, it will deliver amounts of negative-sequence current to the grid. On the contrary, balance transformer will restrain the generation of negative-sequence current to some extent, and reduce the harm to power system.A new method of balanced connection for the auto-transformer(AT) power supply mode where the main traction transformer is responsible for the voltage converter and the feeder auto-transformer structure completes the balance conversion from three-phase to two-phase is proposed in this paper. Because this new method has the advantages of the autotransformer power supply mode and balancing transformer both, it is very appropriate for the auto-transformer power supply system of high speed traction.The relationship between voltage and current of the new balanced wiring structure was analyzed under the circumstances of ideal transformer model. The results proved that it has the balanced ability and its main impedance-balance condition is that the influence of matching impedance to balance relation. Multi-winding transformer theory was adopted to calculate the matching impedance. On the basis of the new method, an improved method was presented. And introduce it briefly including its advantages and disadvantages.Based on the theory of new balanced wiring structure, a mathematical model was established. The mathematical model contains the basic equations, the node admittance matrix in phase coordinates and the relationship between the primary side electrical quantities and the secondary side electrical quantities. This article analyzes the operation of the new balance wiring schemes, and balance condition were added. Based on the analysis results, the node admittance matrix were modified.The scheme can be simulated by MATLAB/simulink, which verified the new method of balanced wiring can fulfill balance transform. The simulation results showed that zero-sequence current was not generated. The simulation of unbalanced load running illustrated the new method of balanced wiring had less effects on the voltage of traction network. Meanwhile, short-circuit current of this new method was simulated as well in this thesis, and its mimic results had been analyzed.