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Unformatted text preview: IEEE TRANSACTIONS ON MAGNETICS, VOL. 46, NO. 8, AUGUST 2010 3249 Physics-Based High-Frequency Transformer Modeling by Finite Elements Nagy Y. Abed I and Osama A. Mohammed P , Fellow, IEEE Quanta Technology, Raleigh, NC 27607 USA Energy Systems Research Laboratory, Electrical and Computer Engineering Department, Florida International University, Miami, FL 33174 USA This paper proposes a computational high-frequency transformer model. The model parameters are obtained by using coupled-cir- cuit-finite-element (FE) nonlinear analysis. The frequency response of the transformer was obtained by coupling the transformer FE model and external electric circuits. This technique would allow the physical representation of the nonlinear magnetization behavior of the transformer as well as the strong frequency dependence of the transformer parameters. The self capacitance of each conductor and the mutual capacitances between the turns were calculated by an electrostatic FE analysis. The capacitance order was then reduced to a lower order by shifting the capacitances connected to internal nodes (windings) to the external ones (coil nodes). The resulting reduced capacitances, along with the inductances and resistances, were then used in the circuit domain of the coupled circuit-FE analysis. The transformer frequency response was then obtained from FE analysis. This response was then fitted with rational function approximation. This rational function approximation is then used to construct a frequency-dependent branch (FDB) which is connected in parallel with the nominal frequency transformer model. The FDB branch represents the transformer high-frequency behavior over a wide frequency range. The implementation is performed on a 125-kVA transformer. The developed model terminal behavior was tested under different operating conditions. This includes different switching frequencies and connecting cable length. Index Terms— Finite-element analysis, frequency-dependent parameters, high-frequency transformer model, vector fitting. I. INTRODUCTION T HERE are different models for transformers for various contingencies. These models are designed to include the effect of core saturation-related problems, ferroresonance, hys- teresis, and insulation issues. High-frequency modeling is essential in the design of power transformers to study impulse voltage and switching surge dis- tribution, winding integrity, and insulation diagnosis and, most often, high-fidelity models in a bandwidth up to 10 MHz are re- quired for condition monitoring purposes [1], [2]. The study of the high-frequency part of the spectra is necessary due to the re- sulting stray capacitances that shunt the series inductances and dominating the response....
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This note was uploaded on 06/08/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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