Analysis on the effects of 500kV main transformer single-phase replacement on differential protection

Combined with the project which studies the feasibility of replacing a 500kV substation No.2 main transformer and based on PSCAD/EMTDC, this paper introduces a special auto-transformer model to study the effects of percentages of three-phase winding short circuit voltage on the transformer differential protection under normal operation and fault conditions after replacing the B-phase transformer for No.2 main transformer with original A-phase transformer for No.1 main transformer. It is preliminarily concluded that the replacement has little effect on differential protection and a certain degree of asymmetry of the percentage of three-phase winding short circuit voltage is allowed, which provides new ideas and references for further study on three-phase transformer single-phase replacement.