Investigation of the harmonic behavior of three phase transformer under nonsinusoidal operation using finite element and wavelet packets

This paper investigates the harmonic behavior of three phase power transformers under nonsinusoidal operations. The terminal behavior of the transformer was obtained by coupling the transformer transient finite-element (FE) model and external electric circuits. Such a technique would allow the physical representation of the nonlinear magnetization behavior of the transformer as well as the strong frequency dependence of the transformer parameters. The harmonic behavior of the transformer currents and the dc load current were analyzed using wavelet packet transform algorithm (WPT). The key findings are, uniform frequency bands resulting from WPT decomposition process of the current waveforms can be used for identification of harmonic components. The flattened input voltage distorted by 3rd harmonic component has the highest impact on the dc load current harmonics (with respect to the sinusoidal case). The peaking input voltage distorted by the 5th harmonic component has the highest impact on the transformer secondary current and the magnetizing current harmonics