Dielectric and physicochemical properties of mineral and vegetable oils mixtures

In order to enhance the overload withstand performance of distribution transformers, the mixed insulating oil of mineral and vegetable oil have been used in thousands of distribution transformers in the power grid of China. During the manufacture of transformers, the residual oil in filling pipeline and storage container can mix with refilling insulating oil. Therefore, the performance of mineral and vegetable oil mixture deserves a thorough survey. In this research, vegetable oil FR3 was mixed with mineral oil Karamay No.25. The chemical, physical and dielectric performance of the oils with different mixture ratios were investigated, including breakdown voltage, acidity, viscosity, fire point, flash point and pour point. The results can provide a guide for the design and operation of transformer filled with hybrid insulating oil.