In the rapid development of AC-DC hybrid system in China

the DC bias phenomenon generated by the operation of DC system has an increasing impact on the nearby transformers. For this reason

a transformer state analysis and quantitative evaluation method considering the influence of DC bias is proposed. Firstly

the influence of DC bias on transformer state is quantified from three aspects of transformer noise

vibration intensity and loss

and a quantitative expression is given. On this basis

a quantitative evaluation model of transformer state considering the influence of DC bias is established

and the data fitting method is used to avoid the subjective influence of artificial experience method. Finally

the effectiveness of the proposed model method is proved through the comparative analysis of actual cases

which qualifies the influence of DC bias on the state of transformer. So

the actual working status of transformer can be effectively distinguished

and the working efficiency of operation and maintenance personnel and the equipment management efficiency are improved.