Application of Finite Elements to High Frequency Transformer Modeling

This paper proposes a high frequency transformer model. The model consists of power frequency transformer model connected in parallel with frequency dependent branch (FDB). The FDB branch represents the transformer high frequency behavior over wide frequency range. The frequency response of the transformer was obtained by coupling the transformer FE model and external electric circuits. Such a 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 turns were calculated by electrostatic FE analysis. The model is reduced to a lower order by shifting the capacitances connected to internal nodes to the external ones (coil nodes). The resultant capacitances are then used in the circuit domain. The obtained frequency response is then fitted with rational function approximation. The implementation is performed on 125 kVA shell type transformer with sandwich coils