| Oil-paper is mainly used as electrical insulation in large electrical power transformers. It is gradual aging under the long-term combined effects of temperature, electrical field, oxygen and water etc, which deteriorate the insulation performance, shorten the insulation life, increase the possibility of insulation accident and reduce the reliability of power grid security. Aging mechanism of oil-paper is the precondition and basis to assessment of the aging condition of paper, predicted insulation life and establishment of anti-aging measures for transformers. It is difficult to explain the detailed chemical mechanisms by characteristic of traditional electrical parameters or aging products. Oil-paper aging relates to not only the molecular structure and supramolecular structure, but also the physical and chemical property under the thermal stress effects, therefore, it is very important for engineering and learning field to understand the aging micro-mechanism and thermal characteristic of oil-paper in power transformers.The thermal aging plays the main role in oil-paper degradation. In order to study oil-paper aging mechanism, accelerated thermal aging experiments in laboratory is performed in the thesis. Kraft paper and naphthenic mineral oil is thermally aged for 370 days at 90℃. The FTIR,UV-Vis and XRD under different aging condition of insulation samples are periodically measured, functional group and supramolecular structure of oil-paper variation with different aging condition are investigated and the kinetic of paper degradation is also discussed in further. Finally, the thermal action of insulation paper molecular and kinetic of pyrolysis are investigated by DSC and TG respectively, kinetic parameters of pyrolysis variation with different aging condition are also analyzed.The results indicate that:①Aging products with C = C conjugated group and C = Ochromogenic group dissolved in oil are produced during oil-paper aging and the aging characteristic groups increase with increasing time.②The DP (degree of polymerization) of paper decreasing directly is caused by breakdown of hydrogen and glycoside bonds which results cellulose inter-or-innermolecular force weakening and the activation energy of pyrolysis decreasing. At the same time, the areas of crystallinity is destroyed and the crystal grain size decreasing during aging.③Crystal type hardly change during the paper aging, the decreasing of DP accord with second-order kinetic model and the decreasing law of DP can be well explained by relative degree of crystallinity.④The molecular chain in amorphous regions of paper occurs"glass transition"with the increasing temperature controlled by programme, but the hygrogen bond without fracture in areas of crystallinity , which explain that thermal reaction activity of molecular in amorphous regions is more higher than that in areas of crystallinity.⑤The temperature of main stage is between 230 and 380℃in insulation paper pyrolysis process and the activation energy is 65～96 kJ /mol . The pyrolysis mechanism change until 330℃and the activation energy of low temperature stage(230～330℃) is less than that of high temperature stage(330～380℃) in main pyrolysis process. So the test temperature can't be set to more higher when normal oil-paper aging process in field is simulated by accelerated aging test carried out in laboratory.
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