Harmonic analysis of transformer excitation currents

Transformer core nonlinearity has been a subject of research in electrical power engineering for many decades. An accurate and simple transformer model that takes into account its iron saturation appears to be lacking. The objective of this thesis is to propose a voltage-dependent model of transformer core nonlinearity that predicts the exciting current waveforms at various supply voltages. The model is composed of the core loss resistance and magnetizing reactance as seen by the fundamental frequency component and a series of parallel-connected harmonic current phasors. The single-phase transformer model is extended to represent three-phase transformers under various connections, including Y/Y, Y/{dollar}Delta{dollar}, {dollar}Delta{dollar}/Y, and {dollar}Delta{dollar}/{dollar}Delta{dollar} both with and without grounded neutral. Laboratory experiments have been conducted to verify the accuracy of the proposed model.