The Analysis of Transformer Magnetizing Current Simulation under DC Magnetic Bias

High voltage direct current transmission(HVDC) and geomagnetic storms can lead to transformer DC magnetic bias, which give a lot of impacts on the transformer. The excitation current test and analysis are the key problems in studying of transformer DC magnetic bias characteristics. Through the transformer excitation characteristic curve under DC magnetic bias, the excitation current expression is derived. By comparing the core structure of the three-phase transformer group and the three-phase core-type transformers, the conclusion that the three-phase transformer group is more prone to DC magnetic bias influence is reached. In order to unify the measure of transformer DC bias tolerance, the concept of DC ratio opposed coefficient is put forward. Under different DC ratio opposed coefficient conditions, PSCAD/EMTDC software are used to simulate two types of transformers magnetizing current waveforms and Ф-I curves. Simulation results verify poorer performance of the three-phase transformer group to bear DC magnetic bias.