This paper presents a thermal model of a power transformer in the form of simple equivalent circuit. The model is established to calculate the top oil and hot spot temperatures. The model parameters are obtained from manufacturer test data and an electromagnetic analysis using finite element method (FEM). The model results are compared with measured data obtained from 250 MVA, 230±8×1.5%/118/21 kV ONAF transformer equipped with fiber optic probes and tested according to a load cycle comprising a short time load up to 2.1 pu. The results are additionally compared with the conventional equations of the IEEE clause 7.
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