Large power transformer-based stray-field loss modeling and validation

A series of transformer-based benchmark models, referred to as Problem 21 Family, are well established to model stray-field loss generated in the structural components of large power transformers. The configuration of the benchmark family, the engineering background of every member model, and the typical measured and calculated results for each model is presented. The new developments of Problem 21, such as the extension to model the saturation state, the electromagnetic behavior inside the laminated sheets, and the variation of iron loss with the excitation current, are highlighted.