Simulation Research on Saturation Characteristics of Converter Transformer due to GIC

The converter transformer working at the rated state will partially be saturated,when GIC invades a power system via the grounded neutrals of transformer.Its magnetizing current will be distorted accompanying with various harmonic and reactive power loss,resulting in transformer damage or transformer life reduction,even system voltage reduction,the protective relay malfunctions.The converter transformer saturation model founded in the paper is based on UMEC(Unified Magnetic Equivalent Circuit) theory.With the model founded,detailed simulations are made about the converter transformer magnetizing current,the harmonic characteristics of the primary-side and secondary-side current of the converter transformer and the reactive power characteristics by PSCAD simulation software.Finally,this paper proposes some cure strategies to restrain converter transformer DC biasing.