A New Model for Inrush Current in Three-Phase Transformers

This study proposes a time-domain analytical–numerical method for accurately evaluating the inrush current in three-phase, three-limb core-type transformers, incorporating the nonlinear magnetic behavior and loss mechanisms of the iron core. The formulation is based on a system of differential equations that describes the dynamic coupling between winding currents and core fluxes. Nonlinear magnetization is modeled through the differential permeability in each core section, defined as the instantaneous slope of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i>–<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> curve, characterizing the flux-density response to incremental magnetic-field variations. The scalar Jiles–Atherton hysteresis model is employed together with eddy-current and excess-loss components to represent the magnetic behavior with physical consistency. The method requires knowledge of the winding turns, which can be readily obtained from auxiliary-coil test, ensuring practical applicability to transformers in service. This modeling approach enables the simulation of transient inrush currents. The simulation results were compared with experimental measurements, showing that the peak inrush current differed by only 1.27% from the highest current amplitude observed in phase C, thus validating the effectiveness of the proposed model for inrush current analysis.