Engineering-Oriented Electromagnetic Property Modeling Of Ferromagnetic Material In Power Transformers

The electromagnetic property effective modeling of electrical materials is the key to improve the prediction results of engineering electromagnetic field problems and validate the electromagnetic design in electrical engineering. However, the materials performance data provided by the material suppliers are, in general, not sufficient. Therefore the complemental material property modelling regarding the material actual working situation is particularly important.The numerical implementations of the eddy current analysis methods based on the different potential sets, such as A- V-A and T-ψ-ψ, are derived, taking the nonlinear and anisotropic properties of electrical materials into account in the finite element analysis of 3-D electromagnetic fields.Secondly, the multi-direction magnetization curves of the grain-oriented silicon steel sheets, 30P120 (made in Korea), sampling at different angles to the rolling direction, have been measured using the Epstein frame. The effects of the different sampling angles on the magnetic properties of the grain-oriented (GO) silicon steel are examined, then the parabolic model (for non-saturated status) and hybrid model (for saturation) are proposed to properly somulste the magnetic property of the silicon steel with different angles to the rolling direction. It is proved that the proposed models have higher simulation accuracy than the classical elliptic model, which is helpful to accurately solve the practical engineering problems.Thirdly, the magnetic properties of the power transformer laminated core are usually measured under the standard condition, which can not completely represent the practical working properties. An efficient method for modeling the global magnetic properties of the laminated core under the actual working condition is investigated based on two core models of product level, which have the same joints but different limb length. The magnetic property data of the laminated core are obtained, such as the effective magnetic path length, the magnetization curve, the loss curve, and the exciting power at both the joints and limbs, which can be used in the electromagnetic analyses and optimization design in power transformers.Fourthly, based on P21-B and P21-M1 of TEAM (Testing Electromagnetic Analysis Methods) Problem 21 Family, the effect of the excitation patterns on both the iron loss and flux inside the solid magnetic steel plate and the GO laminated silicon steel sheets are investigated in detail. The different electromagnetic behaviors of the laminated or solid magnetic steel under the interaction between individual excitation sources are also examined. Some practical approaches are proposed to solve the nonlinear and anisotropic eddy current-hystresiss problems under 3-D excitation conditions. All the calculated and measured results of both iron loss and flux for different test cases are practically in good agreement. These have important significance in improving the performances of power transformers.