Study on Effects of DC Current on Transformers during HVDC Systems Operated in Ground-return Mode

摘要

During monopolar operation HVDC systems with ground return, large current flows into earth in earthing polar, which causes the earth surface potential change. The differences of earth potential drive direct currents flow into transformer windings through its neutral and transmission lines. This paper describes the reason of the effect of the flow of DC current through transformers caused half-cycle saturation. On the basis of the data of HVDC system operated in ground-return mode, this paper presents some methods to mitigate DC bias.