Calculation of the Ratio and Phase-Angle Errors of Phase-Shifting Autotransformers

The determination of the ratio and phase-angle errors of a phase-shifting transformer is quite difficult without special test equipment of adequate sensitivity and precision. Although formulas for the calculation of these errors in two winding potential transformers are available, they cannot easily be applied to the interconnected autotransformers used for phase shifting. This paper demonstrates a method for calculation of these errors by the application of Thevenin's Theorem.