Analysis of T-T Connections of Two Single-Phase Transformers

The T-T connected transformer is a connection of two single-phase transformers which will yield the same phasor relation as a standard 3-phase transformer. However, because of the unsymmetrical nature of the T-T connected transformer, undesirable negative and zero-sequence voltages may be introduced into the electric system. Fortunately, these voltages are quite small for a properly designed T-T connected transformer under normal load. A method for determining the induced negative-and zero-sequence voltages (or currents) by utilizing the interconnected sequence impedance circuit for the T-T connected transformer is presented.