Cross-coupled-secondaries model for multiwinding transformers with parameter values calculated from short-circuit impedances

It is demonstrated how it is possible to use the measured or calculated short-circuit impedances for a multiwinding transformer to examine the effects of AC winding resistances and leakage inductances on its operation. For this purpose, the cross-coupled-secondaries equivalent-circuit model is presented along with equations for calculating its parameter values. As long as the transformer operates linearly, at a frequency below that where winding-capacitance effects become dominant, this model accurately predicts the output windings voltages for any connection of a sinusoidal excitation source and linear loads. A comparison of model predictions with measurements of AC voltage regulation demonstrates the robustness of this model for loads with a wide range of power factors. When coupled with a previously published method for calculating the short-circuit impedances of a transformer from its geometry (see V.A. Niemala et al., 1989) this modeling technique should make it possible to eliminate some of the trial-and-error in transformer design. In addition, it can provide a better understanding of the effects that physical design changes have on the terminal characteristics of a transformer.<
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