操作冲击电压累积作用下油纸绝缘的损伤与特性研究-电气工程专业论文.docxVIP

重庆大学硕士学 重庆大学硕士学位论文 英文摘要 II II ABSTRACT Power transformer is the core of power grid, which determines the safety of the grid. Studies have shown that the main reason for the failure of transformers is the aging of oil-paper insulation, which is caused by various factors such as temperature, electric, moisture and oxygen. In order to monitor the status of the oil-paper insulation, the damage to the oil-paper insulation caused by each aging factor must be studied. In all these aging factors, the influence of overvoltages can’t be ignored. However, there’re just a few research on the damage of the oil-paper which caused by overvoltages. What’s more, most of the research focused on the effect of lightening impulse. There are few reports about the research on the influence of switching overvoltages to the oil-paper insulation. In this paper, a research about the damage and characteristic of oil-paper insulation under the accumulative affect of switching impulse was made by establishing a test platform. The results showed that there will be spark and arc discharges on the surface of insulating paper under the affect of switching impulse, which will increase the contents of H2 and hydrocarbon gases dissolved in the insulating oil. At the same time, the polar material which is produced by the discharge will increase the dielectric constant and dielectric loss of insulating oil in the low frequency domain. The dc conductivity of insulating oil also increases while the breakdown and partial discharge characteristic keep steady. At the same time, the discharge will decrease the surface conductivity of insulating paper, which leads to the decrease of the inception voltage of surface discharge. Part of the molecular chains in the insulating paper will fracture under the accumulative affect of switching impulse voltage, which leads to the decrease of the degree of polymerization of insulating paper. The dielectric constant and dielectric loss of insulating paper will increase in t