Numerical Simulation and Experimental Validation of Coupled Flow, Heat Transfer and Electromagnetic Problems in Electrical Transformers

Abstract

The paper presents a state-of-the-art of the numerical modeling of the coupled problems involving heat, fluid flow and electromagnetic phenomena in electrical transformers. Mathematical descriptions of both Computational Fluid Dynamics (CFD) and electromagnetic (EMAG) models are given. Since these models include other submodels for a definition of boundary conditions as local and temperature-dependent convective and radiative heat fluxes, heat generation terms, temperature-dependent and effective values of material properties for different constructions of coils etc., the component problems published in a subject literature are also reported. Moreover, a coupling procedure of the CFD and EMAG solutions to examine the specific power losses within coils and a core is outlined. On the basis of the mathematical model, a numerical example of a three phase medium-power dry-type electrical transformer is presented. A validation of the numerical calculations is performed using the experimental transformer temperature tests in the short-circuit, open-circuit, and under rated parameters according to the current European Standards for dry-type transformers. During the tests, temperatures were measured at selected points on transformer elements using thermocouples and thermometers, while on the external tank walls an infrared thermography was employed.