Estimation of the hottest spot temperature (HST) in power transformers considering thermal inhomogeniety of the windings

The degradation of electrical insulation in transformers is traced to thermoelectric processes. Existence of localized hot regions due to thermal insulating properties of electrical insulation would cause thermal runaway around these regions. In an earlier paper [1], the authors presented analytical methods for estimating the temperature and its distribution at different points of the transformer based on a closed-form mathematical technique using a generalized heat conduction (GHC) model. Certain aspects of the inhomogeniety of the several components of the winding and incorporation of distributed heat source were not addressed. Also, a rigorous treatment involving the changes in winding resistance, which was built into the thermal model as an empirical correction factor, has now been modified and incorporated in the GHC. These considerations have now improved the accuracy of estimation of hottest spot temperature.