Based upon the analysis of an equivalent circuit for distribution transformer with three windings, an engineering calculation method for the reactance and parameters of this transformer is introduced.

Its software is designed to calculate the running parameters of the AC drive system, including transformer, quadrant rectifier, DC circuit, inverter, AC motor and train load.

Through this research, a series of difficult technical problems on parameter optimization and on calculation of the content and loss of harmonic waves, etc. have been solved.