A new model for predicting hottest-spot temperature in transformers

This paper presents an investigation into the adequacy of the IEEE hottest-spot temperature (HST) model, when the model parameters are to be determined from measured field data. Because of the inadequacy of this model, a modified version of the IEEE HST is proposed to account for the effects of dynamic variations of the top-oil temperature (TOT) on HST. The calculation of HST traditionally relies on a balanced load assumption. For the practical case when the load is unbalanced, equations are developed to estimate the individual load profile on each phase from the HST on each phase and the total load. The IEEE HST model and its modified version are used to estimate the parameters of two different transformers. The results of the parameter estimations are provided and conclusions about the two models are drawn.