Frequency-Dependent Modeling of Transformer Winding Impedance From R(ω)/L Measurements

We describe a practical modeling approach for including the frequency dependency of transformer winding resistance in Electromagnetic Transients Program-type simulation tools, based on typical curves of R(omega)/L ratios. From the given resistance component, the inductance component is calculated via Kramers-Kronig dispersion relations. The resulting impedance is subjected to low-order rational approximation impedance by a Foster equivalent circuit. The proposed model can be easily applied to any transformer in the range of 20-500 MVA by rescaling the given Foster circuit parameters by the 50-Hz winding resistance.