| The transformer oil-paper insulation is a complicated physical and chemical change process. It not only involves the action of electric field stress, but also the action of other environmental stresses such as hot stress and mechanical stress. In recent years, the domestic and international scholars have begun to regard physical and chemical changes in the aging course as the key research object. They attempt to expose the relationship between structure and property of the oil-paper insulating materials from microcosmic perspective to explain the connection between micro-structure and macro-properties of oil-paper. At the beginning of the 1990s, with the quick development of Hi-Tech, as a kind of totally independent and novel research means, the application of molecular simulation in material science enters a new stage. Molecular simulation is a kind of technology using computer to imitate the molecular structure and behavior based on molecular model of atom level, besides being able to get the accurate property data, it is can also used to get a deeper understanding to the mechanism of various complicated phenomena. Molecular simulation is considered one of the most promising solutions to realize this goal.The molecular dynamics and computational quantum chemistry are used to research the aging mechanism of transformer oil-paper insulation and the application of gas diffusion behavior in this paper.Firstly, the model of cellulose molecule is built up, the LUMO-HOMO energy gap changing with the direct electric fields is calculated simultaneity. The possible breakdown field of cellulose molecule is educed. The chain scission process of cellulose molecule under certain external environment such as temperature and electric field is analyzed. And we found that chain fracture of cellulose molecule occurs in the weakest glycosidic linkage. The comparison of the dynamics simulated result and atomic force microscopy observation before and after ageing proves that the electrical-heating aging can destroy the cyclic structure of glucose actually and it can produce some active groups. Through comparing and analyzing the molecular simulation result and surveying value of the infrared spectroscopy of cellulose, the vibration characteristic group's position can be confirmed. The degradation mechanism which can be analyzed by active groups is put forward.Then, the crack probability analysis of paraffin base oil is given by molecular simulation. The cracked temperature of paraffin base oil is established and the impact of temperature on hot cracked reaction rate of paraffin oil is analyzed. Besides, the activation energy of cracking reaction is calculated. The result indicates that the hot cracked reaction rate of paraffin base oil quickens with the increasing of temperature. In addition, the generation mechanism of gas dissolve in oil and its course are analyzed from molecular dynamics. The result reveals that high temperature quickening molecular motion speed is the reason of molecular splitting. And electric field stress plays a enormous tension effect on molecular chain along electric field function, which promote the cleavage of the molecule. There are a lot of free radicals such as carbonyl, methane and Hydrocarbons engendered in the progress of oil cracking. These unstable intermediates form the steady light molecule hydrocarbon gases through a sequence of steps such as gas reset, cleavage, as well as hydrogen transformation.Finally, the self-diffusion coefficients of paraffin base oil and paper system are calculated by molecular dynamics under COMPASS force field. The effect of temperature on carbon dioxide in oil insulation and paper insulation is simulated. Using free volume theory to describe the diffuse phenomenon of gas in the oil is proposed. The free volume theory has a significant sense to understand the diffusion behavior of small molecule gas in the oil.Our understanding of micro aging mechanism of oil-paper insulation and the essential of gas diffusion phenomenon are enhanced through the research of this thesis, and the research means of molecular dynamics and its application are widened at the same time. And it has offered a strong support for mass use of molecular dynamics method in the field of high voltage insulating material.
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