CALCULATION OF SPATIAL LOSS DISTRIBUTION IN STACKED POWER AND DISTRIBUTION TRANSFORMER CORES

This paper describes an analytical solution to use a generic 2D finite difference method to accurately calculate the Quasi 3D spatial distri bution, components, and total core losses in transformer cores. The so lution takes into account 1) Magnetic anisotropy and nonlinearity of t he cole material, 2) All components of iron losses of the core materia l; including losses in directions other than the rolling direction, an d 3) joint model & localized losses due to the distorted flux distribu tion in the joint regions (due to core gaps) across the core-stack. Wi th above attributes considered in the analysis, one is able to use the results to 1) calculate very accurately the total core losses of a tr ansformer at the design stage every time; for all care materials, at a ll operating inductions, for all core geometries, and for both 50 Hz a nd 60 Hz, 2) Understand the contribution of cross losses, harmonics, a nd joints to the total losses of a core, 3) Evaluate the impact of var ious joint attributes, such as, type of joint, number of steps, number of laminations per step, size of gaps, and lamination thickness on th e total performance of the core, and 4) improve the core loss performa nce of transformers by optimizing core design and core material parame ters. This paper presents the analysis as applied to 3-phase, 3-limb c ores. Other 1-phase and 3-phase core geometries will be the subject of a subsequent paper. The paper also presents the results of the extens ive experimental/test verification performed on a number of model core s in the lab as well as on a large number of actual commercial transfo rmer cores with excellent agreements. The results of this analysis hav e been used in developing the new design practice at ABB worldwide to calculate core Losses of stacked power and distribution transformers w ith consistent accuracy.