New Thermal Model for Accurate Prediction of Top Oil Temperature of Distribution Transformer

The purpose of this paper is to present an advanced physical thermal model to accurately predict the top oil temperature (TOT) according to laboratory measurement data. The measurands are the ambient temperature (AT), TOT, and loading factor. An important feature of this thermal model is the consideration of the four thermal points of the environment, radiator, top oil, and winding. Temperature-dependent nonlinear resistors model the heat transfer between these points. Each point represents the temperature change of that part. The experimental results for a 50-kVA ONAN cooling distribution transformer verify the proposed thermal model. It demonstrates that the model is very precise for calculating TOT. Comparing the predicted and measured TOT can be used to diagnose the transformer fault.