Leakage Inductance Representation for a Magnetic Circuit Model of Three-Winding Transformers for Electromagnetic Transient Analysis

Abstract

In order to study electromagnetic transient phenomena occurring in power systems such as inrush currents or ferroresonance, an accurate and practical three-winding transformer model is required because the power system to be studied includes three-winding transformers in many cases. Although a star-circuit representation (Steinmetz's equivalent circuit model) is often used for these kinds of studies, it sometimes causes numerical instability because its magnetizing circuit representation is inappropriate. A magnetic circuit model considering iron-core topology is capable of eliminating the problem. However, the conventional three-winding magnetic circuit model does not match the leakage inductance measurements (short circuit tests) of the transformer to be represented. In this paper, we develop the three-winding magnetic circuit model which can match the leakage inductance measurements by making use of mutually coupled magnetic resistances. As a result of verification using a 500 VA single-phase three-winding transformer, it is indicated that the leakage inductance calculated by the developed model are in good agreement with those obtained by the leakage inductance measurements of the test transformer.