Three-phase transformer modeling for unbalanced harmonic power flow studies

This paper analyses a simple and systematic three-phase transformer modelisation under unbalanced conditions. This modelisation is derived from the primitive admittance model of the three-phase transformers and it is based on the short-circuit impedance value. The transformer sequence component characterization is obtained from this model too; it allows to obtain the sequence equivalent circuits of the different transformer configurations systematically. The transformer model is incorporated into three-phase harmonic load flow software. Different examples are presented to study the impact of different three-phase transformer connections on harmonic voltage distribution