Thermal properties of a mixture of mineral oil and synthetic ester in terms of its application in the transformer

The article presents an analysis of thermal properties of a mixture of mineral oil and synthetic ester used in transformers. The oil/ester rate was as follows: 100%/0%, 95%/5%, 80%/20%, 50%/50%, 20%/80%, 5%/95%, and 0%/100% The measured thermal properties were: thermal conductivity, specific heat, viscosity, density, and the thermal expansion factor. On the basis of measurement results, the authors calculated the heat transfer factor α. This factor determines the ability of a liquid and it has the key influence in transformer cooling. The measurements were done for a wide temperature range from 25 to 80°C.