Enhancing Dielectric and Thermal Performances of Synthetic-Ester Insulating Oil via Blending With Natural Ester

Synthetic ester and blended insulating oils have attracted widespread attention owing to their great potential on performance enhancement because of the high capacity with tailorable molecular structure and mixable components. In this work, natural ester insulating oil (FR3) is blended into the synthetic tetra-ester insulating oil (KA) via mixing and oscillating. The physicochemical and electrical property measurements of the ester blends indicate that the flash point, fire point, and ac breakdown voltage of KA are capable to be increased, and the dissipation factor of KA is reduceable by the addition of FR3. As expected, a series of physicochemical properties of the ester blends follow a quasi-linear relationship with the variation (in vol%) of FR3. However, the flash point (closed cup) is verified with high nonlinearity according to the results of thermogravimetric-derivative and thermogravimetric-differential scanning calorimetry (TG-DSC) tests in nitrogen. The optimized ester blend [85 vol% (KA):15 vol% (FR3)] is typically manifested by high flash point (260 °C), low pour point (-51 °C), low dissipation factor (1.44%), high ac breakdown voltage (76.5 kV), and high onset temperature of DSC either in nitrogen (229.99 °C) or in the air (272.05 °C). The activation energy is analyzed based on the Arrhenius equation, dissipation factor, and resistivity values to recognize the optimum ratio of the ester blends.