A new type of mixed vegetable insulating oil with better kinematic viscosity and oxidation stability

Abstract

• The molecular dynamics model of mixed vegetable insulating oil with different proportion was established. • The effects of different mixing ratios on the kinematic viscosity of mixed oil were studied by molecular dynamics. • The difference of oxidation stability between palm fatty acid ester and rapeseed oil was studied by First-Principle. • A mixing ratio with good kinematic viscosity and oxidation stability was obtained. Natural ester is a new type of environment-friendly energy, and the research on its performance is crucial in order to be widely popularized and applied in electrical equipment. The mixing of different natural esters can ameliorate the performance handicap of natural esters. Therefore, two widely applied natural esters, rapeseed oil and palm fatty acid ester (PFAE) were selected in this paper. The kinematic viscosity and oxidation stability of mixed oil were analyzed on the basis of the establishment of the mixture of two oils with different mixing proportion by simulation. Results indicate that the kinematic viscosity of the mixed oil decreased with the addition of PFAE. The kinematic viscosity of the mixed oil decreased by 51.3% when the mixing ratio was 80% rapeseed oil and 20% PFAE. The addition of short chain oil molecules increases the mean square displacement, mean-square radius of gyration and free volume of the mixed oil. The oil molecules in the mixed system have fewer tangles and reduced internal friction between them. DFT calculation shows that numerous electron traps in PFAE provide a channel for the transition of valence electrons. The methyl group in PFAE has strong positive electrostatic potential and strong electron affinity, which makes the oxidation stability of PFAE lower than that of rapeseed oil. Therefore, 80% rapeseed oil and 20% PFAE are the best mixing ratio in this study. This ratio has the best improvement on the kinematic viscosity of the mixed oil and the least influence on the oxidation stability.