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Calculation of 220kV Transformer Bias Current Based on the Earth and Power Grid Model in the Metro Area

The metro stray current will be generated during subway operation, which will affect the electromagnetic environment near the subway, and then affect the surrounding 220kV transformer. In order to analyze the influence of stray current on the DC bias of the transformer, this paper calculates the magnitude of the stray current through the resistance network model, and then analyzes the changes in the surrounding ground potential caused by the stray current based on the earth resistivity model. Finally, the 220kV transformer network topology model of the city network was established, and the relationship between the neutral point current of the transformer and time was obtained. It provided a quantitative method for research the correlation between subway stray current and 220kV transformer bias current phenomenon and calculate the bias current of 220kV transformer in urban network near subway.