Saturated Transformer Inductances Determined By Energy Perturbation Techniques

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Abstract
The effect of perturbation of currents of multi-winding transformers, on the stored magnetic energy in the magnetic field associated with these apparatus is used to calculate the saturated incremental, apparent and effective self and mutual winding inductances. The method is applied here to single phase and three phase transformers. A finite element magnetic field model is used to calculate the energy stored in the magnetic field associated with such transformers. The numerically calculated inductances are in good agreement with those obtained from test. The results of this work reveal that in three phase transformers various winding self and mutual inductances cannot be considered constant or independent of time and level of excitation, throughout an ac cycle of operation. This method, enables one to determine incremental values of transformer inductances during the design stage. Knowing such parameters before construction of hardware is most significant in the dynamic analysis and design of static solid state power conversion equipment, and may help avoid costly design modifications of such apparatus.