General frame of reference for analysis of harmonic distortion in systems with multiple transformer nonlinearities

Although the magnetising nonlinearity of power transformers is recognised as a source of harmonic distortion, its effect is often considered negligible, and the analytical models used to assess such effect are extremely simple. A new and more general power system frame of reference which models the coupling between phases and between hamonics is presented in the paper. The model is applied to a practical system wth several transformers to show that when one or more of these elements operate in the saturation region the voltage harmonic levels can be higher than those permitted by legislation.