Preparation Of Insulating Oil By Vegetable Oil And Its Antioxidation Property

Mineral insulating oil has extensive application in oil-immersed voltage equipment. It has excellent electric insulating property, high coolant capability and low cost. However, it is poorly biodegradable as well and may contaminate soil, waterways, and resident conditions when serious oil spill or leakage occurs. It can't achieve the request of environmental protection. Therefore, research on the environment-friendly vegetable insulating oil has become a pop project.Researches on using vegetable oil as dielectric liquid began at the same time as mineral oil. Because of its weak antioxygenic property and high viscosity, vegetable oil was restricted in capacitor impregnan. From 1990s, the researches of using vegetable oil as dielectric liquid have been developed again. Vegetable oil, extracted from crude seed oil, is fully biodegradable. Nowaday, the reserves of mineral oil became decreased, so vegetable oil could be the green substitute as mineral oil.The rapid method of preparation of insulating oil was studied with rapeseed oil and methanol catalyzed with ionic liquid under microwave irradiation. Factors influencing on yield of insulating oil were investigated following microwave power, microwave irradiation time, dosage and type of ionic liquid, amount and type of catalyst and mass ratio of methanol to oil. The results show that, microwave and ionic liquid had synergetic effect on transesterification when using NaOH as catalyst. Ionic liquid has the effects of catalysis and solubilization, which can eliminate the interface of methanol and oil, and it also can reduce the saponification and improves efficiency of transesterification. Microwave can also improve the transesterification efficiency for its thermal and non-thermal effect. The optimum conditions for preparation insulating oil are as follows: microwave power 1000W, reaction time 10min, reaction temperature 65℃, molar ratio of methanol to oil 6:1, dosage of catalyst 0.8% (mass ratio of NaOH to oil),dosage of ionic liquid 1.5% (mass ratio of [BMIm]BF4 to oil). The yield of insulating oil is 84.6%.The physical and chemical properties, also electric performances of the vegetable insulating oil after microwave-assisted synthesis is tested. The results show that, the flashpoint of the insulating vegetagble oil is higher than 170℃, the dielectric breakdown voltage can reach as high as above 64 kV/2.5 cm, the dissipation factor at 90℃is 0.0087, the volume resistivity at 90℃is 6.43×1010?·m, the high dielectric constant dielectricεr is 3.08, pollution-free to environment, every index can meet well with the requirement for the insulating oil, so it is a excellent substitute of mineral insulating oil.The oxidation mechanism of oil was discussed and the action mechanism of antioxidants was analyzed. Different kinds of antioxidant such as BHT, PG, TBHQ are tested in this study. It is found that the most suitable antioxidant is TBHQ and the optinal dosage for transgenic rapeseed oil is 50ppm.