Detailed High-Frequency Modeling and Experimental FRA Validation of a Multi-Section Transformer Winding

The increasing integration of renewable energy sources, high-voltage direct current (HVDC) and power-electronics-based equipment has intensified the exposure of transformer windings to high-frequency voltage components, steep-front transients and high-dv/dt stresses, highlighting the need for detailed high-frequency winding models. This study presents a high-frequency model of a six-section winding assembly corresponding to one phase of a 10 kV/0.41 kV, Dyn11, 2500 kVA distribution transformer. The winding assembly was experimentally investigated under coreless conditions using frequency response analysis (FRA) measurements over the frequency range of 20 Hz–2 MHz. Frequency-dependent resistance R(f) parameters were extracted from finite element method (FEM)-based electromagnetic field analyses, while the self- and mutual inductance matrix and the capacitance parameters were obtained from electromagnetic and electrostatic field solutions, respectively. The resulting segmented resistance–inductance–mutual inductance–capacitance (R-L-M-C) equivalent circuit model was solved in the frequency domain using Modified Nodal Analysis (MNA). Before the FRA-based validation, the low-frequency consistency of the model was checked at 50.431 Hz, where the calculated and measured magnitudes differed by only 0.1074 dB. Over the common frequency range, the model achieved a root mean square error (RMSE) of 3.09 dB and a mean absolute error (MAE) of 1.76 dB. The results show that the proposed field-extracted model can represent the overall FRA trend, the dominant attenuation region and the main resonance/anti-resonance characteristics of the winding assembly, although deviations remain around sharp resonance points.