Influence of DC magnetic bias on excitation current of transformer

DC magnetic bias is an abnormal working state of a converter transformer,which means that the excitation current contains DC component.DC magnetic bias makes the excitation current rise obviously and magnetic field waveform distort seriously,which leads to different saturation levels in positive-half cycle and negative-half cycle.It makes magnetization curve of the iron core asymmetric and iron core saturate periodically.For this case,2-dimensional transient finite element method coupled with circuit loop was adopted to study the no-load transformer on the basis of DC magnetic bias,which was used to analyze iron core magnetic flux intensity and excitation current in case of the no-load transformer on the basis of different DC magnetic biases.The results indicate that with increasing the DC of a transformer,the higher is the core saturation,and the more serious is the excitation current distortion.