Power Transformer Harmonic and Electro-Thermal Modeling: A Multiphysics Review

Harmonic distortion reduces transformer efficiency, increases temperature rise, and hastens insulation deterioration. This paper reviews transformer modeling approaches for harmonic investigations and proposes an integrated electro-thermal perspective to predict better loss allocation, temperature evolution, and lifespan under non-sinusoidal operations. The modeling approaches are divided into linear and nonlinear equivalent-circuit representations, frequency-domain formulations, time-domain electromagnetic transient models, and electromagnetic-field- and finite-element-based methods, with a focus on how harmonic spectra affect core loss, copper loss, eddy loss, and stray loss mechanisms. Unlike previous surveys, which treated electrical modeling and thermal assessment separately, this review connects harmonic-dependent electrical losses to standards-aligned thermal modeling via equivalent thermal circuits and multi-physics thermal methods, including lumped and network models, computational fluid dynamics, and finite-element-based analyses. The thermal management under harmonic stress is presented, including cooling techniques, insulating fluids, and current developments in hotspot prediction. Electrical-thermal co-simulation, digital twin concepts, and learning-assisted estimators for hotspot temperature and loss-of-life evaluation are all discussed. The resulting unified approach facilitates consistent model selection, parameter identification, and validation planning for dependable transformer operation in converter-and distortion-rich power systems.