The winding hot spot temperature of the oil-immersed power transformer is an important parameter factor in the long-term life of the transformer. It has a great influence on the transformer insulation aging and a close relationship to the transformer top oil temperature which is used to indicate the operating conditions of the transformer. In view of the hot-spot rise over top oil temperature is a function dependent on time as well as the transformer loading, this paper developed a simple thermal model to calculate transformer hot spot temperature based on thermal-electrical analogy, which incorporated the nonlinear thermal resistance and application of oil viscosity and winding losses changes with temperature. The model parameters are estimated by Levenberg-Marquardt method. In the end, The comparison of experimental data under various loadings and model outputs shows the accuracy and efficiency of the proposed model, which suggest that this presented model can describe the thermal behavior of oil-immersed transformer more accurately.
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