Computation of Parameters of Power Transformer Windings for Use in Frequency Response Analysis

We present a 3-D model for calculating magnetic fields in a power transformer and the effective parameters (inductance and resistance) of its windings. The transformer is representative of large transformers with power ratings ranging from hundreds of kilovolt amperes to hundreds of megavolt amperes. The model accounts for anisotropic frequency-dependent properties of the laminated transformer core and eddy currents in the steel sheets. We discuss the results of the calculations performed in the frequency range 10 Hz-10 MHz, and show that the largest variations of both the magnetic field and parameters of the windings take place at frequencies below ~10 kHz and, at frequencies higher than 1 MHz, the magnetic core does not significantly affect the variation of the effective parameters