Research On Direct-Current Magnetic Bias Of Large Power Transformer

The phenomenon of DC bias is caused by the electric potential difference between the earthing neutrals of transformer. The influence of DC magnetic bias on transformer is concerned by the designers, producers and users. The phenomenon of DC magnetic bias analysis and electromagnetic field calculating are combined in this paper and the running performance is simulated with different magnetic bias DC.Firstly, the reasons of DC magnetic bias on transformer are studied. The range of bias DC is determined according to the measuring data of earthing neutrals DC of transformer, and the influences of DC magnetic bias on transformer are studied.Secondly, 2D model of transformer is built according to the structure size of transformer in this paper. The values of excitation current with different bias DC are calculated using the 2D nonlinear field-circuit coupled fem and the core's working condition of transformer is analyzed with different magnetic bias DC. The increasing of DC magnetic flow leads to the core saturated and causes the waveform of excitation current dissymmetric and the peaked wave appearing in positive half cycle. Besides, the eddy current losses in the metal component and the distribution of leakage magnetic field with different magnetic bias DC are calculated respectively using 2D and 3D nonlinear field-circuit coupled fem. The losses effect caused by leakage magnetic with different bias DC is analyzed.At last, the temperature-rise of transformer is calculated using the temperature field method and the influence on DC magnetic bias to temperature-rise is analyzed. According to the analysis results, the permission criteria of transformer DC magnetic bias is discussed and supplies reference for engineering practice and theoretical research.