my country's AC/DC hybrid transmission mode has gradually formed, which has also led to the problem of mutual interference between AC and DC systems. When the DC line has a single-maximum loop operation, the DC current flowing into the earth through the grounding pole of the DC system will have an impact on the power transformer in the AC power system. The main manifestation is that the neutral point of the transformer flows through the DC and the core is biased. The DC bias causes the transformer vibration to increase, the noise increases, and the harmonics increase.