Simple Equivalent Circuit Capacitance Model for Two-Winding Transformers

Abstract

This paper highlights how a currently available transformer equivalent circuit model incorrectly represents the transformer performance, in scenarios where both sides of the transformer are fixed to a common reference-point. A new transformer equivalent circuit model is presented which accurately predicts the transformer performance. A thorough analysis of the proposed model and a commonly used model is compared and presented. Three foil-wound and three wire-wound transformers with different turns ratio are constructed, with the purpose of evaluating the accuracy of the transformer models impedance prediction. Both models accurately predict the transformer impedance for a turns-ratio equal to one. With turns-ratios different from one, the commonly used model predicts wrong impedance, whereas the proposed model remains accurate. The error in the predicted equivalent capacitance of the measurements is between 32%-170% when using the commonly used model, while it is only 0.6%-9.8% when using the proposed model. The proposed model is therefore the only model that provides accurate impedance analysis for any turns-ratio in any operation scenario.