Fourier-based effective permeability for transformer iron losses computation under saturation

Abstract

Computation of iron losses in transformers requires significant numerical efforts, particularly under magnetic saturation when the magnetic non-linearity needs to be considered. This study proposes a Fourier method to calculate the magnetic flux density used for the iron loss evaluation in transformers under saturation. It includes pre-processing of the non-linear material. A permeability frequency spectrum is obtained from Fourier analysis, where the fundamental part is used as a magnetisation definition and the harmonic components are used for core loss calculation. The proposed method offers a time-efficient tool to calculate core loss under various saturation levels and non-sinusoidal excitation currents. The influence of the definition of the core material on the leakage field and the stray loss calculation is studied and compared with existing methods. The proposed methods have been implemented and validated in two- and three-dimensional finite-element models with isotropic and anisotropic cores. The results yield accuracy comparable to that of a time-domain calculation. Furthermore, the influences of various effective permeability methods on the leakage field and the associated stray loss are compared and discussed.

Fourier-based effective permeability for transformer iron losses computation under saturation