Aging Characteristics Research Of Polymer Material In Mineral Oil Under Thermal Aging

Oil-paper insulation is a key type of internal insulation in oil-immersed transformers; its performance and quality are directly related to the reliability and service life of the transformer. Insulation paper has some defects such as high dielectric constant, poor high temperature resistance and easy decomposition characteristics, which have limited the development of oil immersed transformer towards large capacity and small volume. Therefore, finding new insulation material with excellent insulation performance and good high temperature resistance to replace insulation paper will make it possible for the development of transformer towards large capacity and small volume.In this paper, PC and PET are chosen to make a contrast with insulation paper by conducting aging tests for 300 days at 90℃,110℃ and 130℃. In this experiment, solid material properties and oil properties are mainly studied. Besides, degree of polymerization, mechanical properties, surface roughness, thermodynamic analysis, dissolved gas and product in the oil are tested respectively.From the experiment we can see, the degree of polymerization, elongation at break, surface roughness and oil production can be used to characterize the aging degree of three kinds of insulation material; pyrolysis characteristic value, the enthalpy and the dissolved gas in the oil can be used to characterize the aging degree of insulation paper, but these are failed to characterize the aging degree of PC and PET. In terms of change rate of the characteristic parameters, that of insulation paper at different temperature is the fastest while the change rate of PC at 90℃ is the slowest; PC and PET are equivalent at 110℃ and the latter shows slowest after a long aging time at 130℃. That is to say, the performance of insulation paper at three kinds of aging temperature is the worst. Aging resistance of PC is the best at 90℃; PC and PET is almost the same at 110℃; when it comes to a long time using at 130℃, PET is better than PC.The long time operating temperature of transformer ranges from 75℃ to 85℃ and the highest temperature can only run up to 98℃, so the condition of long-term working at 130℃ will not show up. Therefore, it has excellent development prospects and further research value for using PC material to replace insulation paper in oil immersed transformer.