Thermal Aging Characteristics of Newly Synthesized Triester Insulation Oil

High-stability triester insulation oil derived from the trimethylolpropane esters (TME) was synthesized by esterifying saturated fatty acids and trimethylolpropane (TMP). The TME oil shows higher AC breakdown voltage (Vb, 72.6 kV/2.5 mm) than that of FR3 (65 kV/2.5 mm). TME oil is readily biodegradable whose biodegradation is 82.2% after 28 days. Pressurized differential scanning calorimetry (PDSC) was applied to measure oxidation onset temperature (OOT) of TME oil for initial evaluating the oxidation stability. Due to the elimination of the carbon-carbon double bonds and β-H, the OOT of the TME oil without antioxidants is approximately 25°C higher than that of FR3. To evaluate the realistic performance of the TME oil, the effect of transformer materials on the aging behavior was investigated. The effect of transformer materials on the thermal aging of TME oil and mineral oil (MO) is less than that of FR3. Although the moisture content and acid value in TME oil induced by aging are higher than those in MO. These acids and moisture do not cause obvious degradation of breakdown voltage and dielectric loss factor, which may be attributed to the high moisture solubility in it.