Method for identifying sympathetic inrush current and fault current in transformer protection

The invention discloses a method for identifying sympathetic inrush current and fault current in transformer protection, and solves a difficult problem in accurate identification of the fault current and the sympathetic inrush current of a transformer. When any one of A phase difference current, B phase difference current and C phase difference current is not lower than a difference current setting value delta I of the transformer, a difference delta S between the high-voltage-side secondary current area Sy(high voltage side) of the transformer and the medium-voltage-side secondary current area Sy(medium voltage side) of the transformer is calculated; when the area difference delta S between the high-voltage-side secondary current area Sy(high voltage side) and the medium-voltage-side secondary current area Sy(medium voltage side) is greater than a current area difference setting value of the difference between the high-voltage-side secondary current area and the medium-voltage-side secondary current area, and a difference between a fundamental wave phase angle of high-voltage-side secondary current and a fundamental wave phase angle of medium-voltage-side secondary current is not greater than 90 degrees, the current of the transformer is the external fault current or the sympathetic inrush current. The method can be used for accurately identifying the fault current and the sympathetic inrush current of the transformer, so that false operation of differential protection of the transformer is avoided and normal running of main equipment of a power grid is guaranteed.