A Novel DC Bias Suppression Method Considering the Cooperation of Multiple Devices

The dc bias phenomenon caused by the excessive current of the neutral point will pose significant threats to the transformers. The conventional suppression method based on capacitive dc blocking device (BD) can prevent dc bias current from penetrating the transformer winding and is the most widely used. However, due to the high investment cost of the BD, it is not appropriate to install the BD for all transformers around the grounding electrode. Thus the BD may redirect the dc flow from one transformer with a BD to the peripheral transformers without BDs, causing the neutral current to exceed undesirably. To address the problems above, a new type of current balancing device (CBD) is introduced, which can lead to flexible suppression of neutral current. Based on coordination between the BD and CBD, a global optimization configuration method is proposed. Unlike the existing suppression strategy based on dc bias suppression devices, the proposed method optimizes the configuration of suppression devices for each transformer from a global perspective in the planning stage, which is an effective supplement to the current suppression method. MATLAB-based simulation results verify the effectiveness and superiority of the proposed method by numerous comparative case studies.