| DC transmission system has been widely applied in our country,during mono-polar operation of DC system with ground return, part of the DC in the land through transformer neutral point, DC through the other side of the transformer into the transformer neutral point by AC system, and constitute circuit. The theoretic baffling problems concerned have been researched. It affects normal running of power system. Because the transformer core is different, the effects are also different.EMD and Hilbert transform are applied in simulation study under DC bias. By use of MATLAB, simulation model of DC bias is established. The results show that DC voltage increases, the distortion of exciting current increases. By EMD method, extracts the IMF1 of the signals. Then the Hilbert transform is applied in IMF1 to obtain the instantaneous frequency and amplitude. With this method, the time,frequency and amplitude information of the exciting current distortion can be accurately detected. EMD is first applied in DC bias in this paper, it provides proof for further study on transformer under DC bias based on the theory.Three-phase power transformer is simulated, according to practical parameters of entity, finite element theory, building the 3D solid modeling by ANSYS. When the power transformer run with no-loading, the DC voltage will injected into the neutral point, to see the distribution of leakage magnetic flux of iron core and flux density range of values. 3D model of DC bias is better than 2D model by ANSYS, it can more intuitively and accurately reflect to distribution of leakage magnetic field.Discussing measures of restraining DC bias in system and designing of transformer core about the DC bias. Introduced the transformer neutral point reverse current method, transformer neutral point series resistance method,transformer neutral point series capacitor method, the AC lines series capacitor method, and do a more detailed explanation for their advantages and disadvantages.
|
PDF Full Text Request