Analytical model of a T-connected three-phase transformer Original Research Article

Three-phase transformers usually consist of three sets of windings connected in Wye, delta or zigzag on three individual cores or on a single three-phase one. Two single-phase transformers can also be used in a less than well-known way called the T-connection. Depending on the actual connection, as in conventional three-phase transformers, secondary voltages are in phase or displaced by ±30°. Due to the reduced number of windings, the T-connected transformer can be economically produced. However, since it is an asymmetrical connection, the short-circuit impedances of the individual phases are not identical, leading to unbalanced load voltages and short-circuit currents. An analytical model of the T-connected transformer has been developed to evaluate the effects of the impedance unbalance. This model based on single-phase short-circuit tests can be used to determine voltage unbalances, active and reactive transformer losses and short-circuit impedances.