An electro-thermal modeling of distribution transformer for hottest spot evaluation under photovoltaic-induced harmonics

Abstract

Elevated winding insulation temperature, driven by harmonic distortions, is a key factor in transformer lifespan reduction. Conventional models often oversimplify the effect of combined current and voltage harmonics. This paper proposes an electro-thermal modeling approach, incorporating dual heat sources from core and winding domains, to enhance HST estimation in distribution transformers affected by photovoltaic-induced (PV)-induced harmonic losses. A sophisticated numerical approach, Finite Element Analysis (FEA), is employed using COMSOL Multiphysics software, with a 250-minute time-dependent study assessing thermal effects. The results, verified against a mathematical model approach based on IEEE C57.110-2018 guidance, demonstrate that higher levels of harmonics lead to a rapid increase in HST, accelerating the time to reach the aging factor temperature and consequently diminishing the transformer’s operational lifespan. Specifically, the per-unit life of the transformer decreases from 0.219 in Case 1 to 0.154 in Case 2 and 0.027 in Case 3, while the aging acceleration factor increases from 4.310 to 5.683 and 21.7, respectively. The methods showed over 95% alignment with the mathematical modeling approach, confirming the model’s precision in its predictive capability. The novelty of this study lies in its enhanced electro-thermal framework, which overcomes the limitations of conventional methods by integrating dual heat sources and providing a refined assessment of transformer aging under harmonic distortions. This advancement offers a more precise and computationally efficient approach for assessing transformer thermal stress under harmonic distortions.