Preparation Of Fullerene Nano-Modified Vegetable Insulating Oil And Its Dielectric Properties And Thermal Stability

Vegetable insulating oil is a new environment-friendly liquid insulating medium, characteristic of high fire point, good insulation properties and high rate of natural degradation. It is an excellent green alternative of the traditional mineral insulating oil. However, compared with mineral insulating oil, vegetable insulating oil is not so good because of some defects like high dielectric loss factor, low volume resistivity and poor thermal stability thus easy acidification.In response to the above problems, the paper selects fullerene(C60) nanoparticles to modify vegetable insulating oil, and at the same time modify mineral insulating oil so as to make a contrast for the study of insulating oil modified by C60 nanoparticles. Main works in this paper are as below:① Modify the C60 nanoparticles on surface and prepare the long-term stable vegetable insulating oil and mineral insulating oil modified by C60 nanoparticles. Let the modified insulating oil stand for 12 months and ensure that it is still clear and transparent without any precipitation.② Conduct the electrical performance tests of frequency breakdown voltage, dielectric loss factor and the volume resistivity on vegetable and mineral insulating oil, modified by C60 nanoparticles of different concentrations. The results showed that the addition of C60 nanoparticles shall be suitable. When the concentration of C60 nanoparticles was 100mg/L, the frequency breakdown voltage of modified vegetable insulating oil was increased by 8.6%, the dielectric loss factor was decreased by 20.1% and the volume resistivity was increased by 23.3%. When the concentration of C60 nanoparticles was 200mg/L, the frequency breakdown voltage of modified mineral insulating oil increased by 21.7%; the dielectric loss factor didn’t change significantly; but the volume resistivity was decreasing as the concentration of C60 nanoparticles was increasing. When the concentration of C60 nanoparticles was 300mg/L, the volume resistivity of modified mineral insulating oil was decreased by 45.9%. Select the modified oil samples of the optimum concentration(100mg/L) of vegetable insulating oil, and conduct the lightning impulse breakdown voltage test. The results showed that both polarity of lightning impulse breakdown voltage of the modified vegetable insulating oil and negative lightning impulse breakdown voltage of the modified mineral insulating oil were increased by 8%, except that the positive lightning impulse breakdown voltage of modified mineral insulating oil was increased by 10%.③ Use the widely accepted charge potential trap theory to analyze the stronger breakdown voltage of modified insulating oil. The results showed that the C60 nanoparticles did not produce deeper charge potential trap in vegetable and mineral insulating oil. Considering the electro-negativity of the C60 molecule, the paper puts forward that the stronger breakdown voltage of modified insulating oil was the combined effects of charge potential trap produced by C60 nanoparticles and its electro-negativity.④ The thermal stability of vegetables and mineral insulating oil, modified by C60 nanoparticles, was studied. The tests found that C60 molecules had the nature of adsorbing oxygen molecules, which led to the rapid deterioration of the modified vegetable insulating oil at the beginning of thermal aging. But in the late stage of thermal aging, the dielectric loss factor, volume resistivity, and acid value level were improved, compared with the blank oil sample. And due to the catalytic cracking effect of C60 molecules to alkanes, the results showed C60 nanoparticles were not suitable for mineral insulating oil modification, which meant that nanoparticles choice shall be made suitably according to the base oil and modified target for the insulating oil modification.