Analyzing and Comparing the Hot-spot Thermal Models of HV/LV Prefabricated and Outdoor Oil-Immersed Power Transformers

The most important parameter in transformers life expectancy is the hot-spot temperature level which accelerates the rate of aging of the insulation. The aim of this pa per is to present thermal models for transformers loaded at prefabric ated MV/LV transformer substations and outdoor situations. The hot-spot temperature of transformers is studied using their top-oil temperature rise models. The thermal models proposed for hot-sp ot and top-oil temperatures of different operating situations are compared. Since the thermal transfer is different for indoor and outdoo r transformers considering their operating conditions, their hot-s pot thermal models differ from each other. The proposed thermal models are verified by the results obtained from the experiments carried o ut on a typical 1600 kVA, 30 /0.4 kV, ONAN transformer for both indoor and outdoor situations.