Comparison of transformer loss prediction from computed and measured flux density distribution

Losses in power transformer cores can be predicted from knowledge of localised flux distribution within the assembled laminations. This together with a knowledge of the stress sensitivity of the losses of grain-oriented, 3% silicon iron can ideally be used to estimate the total core loss. The localised flux density is computed given the magnetic material B-H data and the core geometry. This paper reports results in which localised flux density and losses have been measured experimentally in model cores and compared with data obtained from a FEM analysis of the same core geometry. Effects of interlaminar flux, rotational flux and stress are taken into account. Agreement within 5% is found between the measured core loss and that calculated from the localised experimental data but predictions using the FEM results were only within 10% of the measured value. This greater difference is believed to be due to neglect of interlaminar flux and rotational magnetisation in the computation of flux distribution. However, these are shown to be accountable by using corrective factors whose magnitudes depend on core geometry.