Thermal analysis of two transformers filled with different oils

Thermal modeling of power transformers helps ensure that they do not fail prematurely. If a transformer becomes too hot internally, then the insulation materials will degrade faster and the operating lifetime of the transformer will be shortened. The IEC 60076-7 guide states that the working lifetime of nonthermally upgraded paper insulation halves for every 6°C increase in temperature [1]. The thermal cooling capability of an oil is affected by the winding and oil-duct arrangement within the transformer, the ease with which oil flows through the ducts, and the height of the heat exchanger [2], [3]. The insulating oil acts as a coolant, removing heat from within the transformer. The viscosity of an oil affects its cooling capability. Careful transformer design using thermal modeling helps ensure that the cellulosic insulation is adequately cooled, that the oil flows freely around the windings, and that the temperature increase at hot spots is not excessive. When comparing the cooling capability of vegetable oil with that of mineral oil, the following three questions are important