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The lack of data is a hindrance to the experimental determination of magnetic cores characteristics. This work presents a non-invasive and field-applicable methodology for electromagnetic devices characterization. Based on fundamental equations of electromagnetism and routine tests, the methodology was applied to obtain, at low frequency: the core loss separation, the hysteresis loop and its BH curve of a three-phase dry core-type transformer. The required equipment and the procedures to do the characterization are presented and discussed. The results were compared with experimental data obtained from tests that were carried out on the same material using a Single Sheet Tester device. The results show a difference in losses of 4.9% for hysteresis, 1.5% for dynamic, and 3.3% for total losses. In the no-load test comparison there was a difference of 4% for dynamics and 1.8% in total losses. The proposed methodology can be applied to different magnetic core types as well as to single-phase transformers and reactors. [ABSTRACT FROM AUTHOR]

The purpose of this article is to present a wider frame to treat the quasi-static limit of Maxwell's equations. We discuss the fact that there exists not one but indeed two dual Galilean limits, the electric and the magnetic one. We start by a re-examination of the gauge conditions and their compatibility with Lorentz and Galilean covariance. By means of a dimensional analysis on fields and potentials we first emphasize the correct scaling yielding the equations in the two limits. With this particular point of view, the gauge conditions of classical electromagnetism are continuity equations whose range of validity depend on the relativistic or Galilean nature of the underlying phenomenon and have little to do with mathematical closure assumptions taken without physical motivations. We then present the analysis of the quasi-static models in terms of characteristic times and visualize their domains of validity in a suitable diagram. We conclude by few words on the Galilean electrodynamics for moving media, underlying the transformation laws for fields and potentials which are valid in the different limits. [ABSTRACT FROM AUTHOR]

When the total current going through a transformer window is equal to zero, only a negligible part of the magnetic energy reaches its core. This is shown by finite-element-method simulations carried out on several two-winding transformers having different shapes. Moreover, induction and energy-density values obtained by 3-D simulations and by 2-D approximations are very close to each other. These two key observations justify the use of formulas that give the induction created by straight rectangular cross-sectional wires, as used in the partial-element-equivalent-circuit method, to compute the window field and, thus, to value the leakage inductances. To refine this approach, weak magnetic-core effects are accounted for by introducing the magnetic images of currents that flow in the windings. A comparison between the calculated values and measured ones is provided. [ABSTRACT FROM AUTHOR]

The vector and scalar variables describing electromagnetic fields with different requirements of continuity can be identified to four different degrees of differential forms. The association of differential forms with finite elements leads to a set of differential forms based elements (Whitney elements): they are naturally adapted to the discretization of different vector and scalar variables. With the help of a Tonti diagram, Maxwell equations can be classified by two dual sequences together with the constitutive laws of materials. The application of Whitney elements to the two dual sequences leads to two dual approximation schemes. As an example, two dual formulations for eddy current computation using potential variables and the hybrid finite element--boundary element method are derived, where Whitney 3-D and 2-D elements are employed. A numerical application is given at the end of the paper, where the dual features of the two formulations are reported. [ABSTRACT FROM AUTHOR]

Edge-elements are introduced and discussed in the context of complementarity, a desirable characteristic of numerical methods, by which solutions which are equally satisfactory as regards both fields b and h are obtained. By making the vector potential approach easier than with standard nodal elements, edge-elements enhance complementarity. Comparative merits of both kinds of elements are discussed. [ABSTRACT FROM AUTHOR]