The UHVDC projects have been rapidly developed and practiced in recent years because of their advantages of large transmission capacity and long transmission distance. However

the DC bias phenomenon has long existed in the UHVDC projects. The DC bias current will cause the distortion of excitation current

and increase the vibration and noise of the UHVDC converter transformer

which will jeopardize the safe and stable operation of the converter transformer in severe cases. In this paper

the principle of DC bias current was firstly analyzed

then the impact level of a practical UHVDC project was determined by calculation. A UHVDC converter transformer core was constructed to simulate and test its excitation characteristics. The impacts of DC bias on transformer vibration and noise were investigated

and multiphysics coupling modeling and simulation were performed by using finite element method. The research results are of practical significance for guiding the design of converter transformers and for taking the noise reduction measures in subsequent projects.