Calculation of 220kV Transformer Bias Current Based on the Earth and Power Grid Model in the Metro AreaLu Chen, Longfei Wang, Hua Huang, Chunming Liu, Tianyi Wu, Lei Su and Dandan ZhaoE3S Web Conf., 233 (2021) 01050DOI: https://doi.org/10.1051/e3sconf/202123301050