Simulation and Analysis of DC Magnetic Bias in Zhejiang Power Grid

Nowadays, there are two high voltage direct current (HVDC) transmission lines to Zhejiang Province. When HVDC transmission system is operated in ground return status, it will bring about DC magnetic bias of transformers nearby, which is adverse to normal operation of Zhejiang power grid. In this paper, a comprehensive electromagnetic transient model based on PSCAD is built, which covers the whole Zhejiang power grid. The DC magnetic bias phenomenon caused by different HVDC transmission unipolar operation is simulated and analyzed. The results show that, the closer the substation is to the grounding pole, the worse the DC magnetic bias will be. Besides, the capacitive isolation device is adopted to suppress DC magnetic bias for comparison, and the results also verify the effectiveness of the capacitive isolation device.