Study On Preparation And Thermal Aging Characteristics Of Insulating Oil Comprised Of Medium Chain Trimethylolpropane Ester

Natural ester insulating oil is a high-ignition,green and environmentally friendly liquid insulating dielectric.It has been popularized and applied in distribution transformers,but its high kinematic viscosity and weak oxidation stability limit its application.The development of a vegetable oil-based ester insulating oil with high oxidation stability has important academic significance and engineering application value for the development and application of safety and environmental protection transformers.In this paper,the effect of the molecular structure of the triol ester on the thermal oxidation stability was studied,and the molecular structure of the triol ester with high thermal stability was obtained.The medium chain trimethylolpropane（TME）insulating oil was prepared by esterification synthesis.The experiment studied the thermal aging characteristics of TME insulating oil.The main contents are as follows:（1）The effect of alcohol molecular structure and fatty acid chain length on the thermal oxidation stability of triol esters was studied.Esters of different chain length saturated fatty acids（chain lengths 8-18）and different types of triols（glycerol,trimethylolpropane,trimethylolethane）were constructed.Reax FF（Reactive Force-Field）reaction force field was used to simulate the thermal oxidation process of triol esters,and the differences in thermal oxidation stability were compared.Screen triglycerol esters with high thermal oxygen stability and compare with the thermal oxidation path and products of natural esters.The results show that alcohols withoutβ-H make the ester molecules more thermally stable,and the shorter the fatty acid chain length,the higher the oxidation stability.In the thermal oxidation process,the C=C double bond is more likely to initiate the free radical oxidation process and polycondensation reaction.Therefore,triol esters with better thermal and oxygen stability should be free ofβ-H alcohols and have shorter chain lengths.（2）TME insulating oil was prepared by esterification synthesis method.The effect of factors such as reaction temperature,catalyst type,and molar ratio of alkyd acid on the yield of TME insulating oil was studied.The single-factor test method was used to optimize the process parameters and determine the optimal reaction conditions.Study the influence of purification methods such as alkali refining and adsorption on the performance of TME insulating oil,and optimize the purification process.The optimal reaction conditions for the synthesis of TME:the molar ratio of alkyd acid is 1:3.2,the temperature is 140°C,the catalyst is 0.8 wt.%Sn Cl₂,the reaction time is 5 h,and the yield reaches 96.8%.After two alkali refining and three water washings,TME performance reaches the insulating oil standard,and the use of alkaline alumina adsorption instead of alkali refining can avoid post-treatment problems.The prepared TME has a higher ignition point（298°C）and a lower pour point（-45°C）,and its oxidation stability is comparable to that of mineral oil.（3）The thermal aging characteristics of TME insulating oil were studied,and the changes of oil parameters（moisture,power frequency breakdown,dielectric loss factor,etc.）with thermal aging time were obtained.By comparing the performance with natural ester insulating oil after thermal aging,the anti-aging mechanism of TME insulating oil is analyzed.The results show that TME insulating oil can inhibit the occurrence of hydrolysis due to the steric hindrance effect of branched chain alcohols,so it is less likely to hydrolyze than natural esters during thermal aging.TME has good thermal and oxygen stability,and is not prone to polycondensation and polar substances.Therefore,the kinematic viscosity is almost unchanged after aging,and the degree of degradation of dielectric properties is low.