Study on DC Bias Magnetic Properties of Transformer with Different Structures

When the HVDC works in mono-polar operation or bipolar unbalanced operation, DC flows through the neutral point and causes DC bias magnetic of transformer around HVDC grounding electrode, which influences the operation security of transformers. Beside highly saturated core, it also causes the distortion of exciting current, increasing harmonics and leakage magnetic flux, and thus the losses, which in turn results in the structures of transformer overheating and insulation aging. Based on the principle of transformer DC bias magnetic and UMEC of transformer in PSCAD/EMTDC, electromagnetic transient simulation platform of transformer DC bias magnetic is built. Considering the effect of DC bias magnetic on different structure of transformer, three kinds of typical transformer that has been widely applied are selected including three-phase three-limb transformer, three-phase five-limb transformer, three-phase bank transformer. After comparing the differences between these three kinds of transformer, related parameters are set such as the core structure and mode of winding connection and so on.