Study On Aging Characteristics Of110kV Insulating Cross-linked Polyethylene Materials

Cross-linked polyethylene and polyethylene are both widely applied to cableinsulating materials by virtue of their good electric, mechanical, physical andchemical properties.With the rapid development of modern industry，the demand of electric powersupply is increasing at a high rate of speed. In order to satisfy the electricity demandand the economy of power transmission, the power grid is developing in the directionof high capacity and high voltage. On this occasion, higher request is broughtforward in the load and withstand voltage level of the power cable, which causes aworse running environment of the cable. And this can accelerate aging process, forinstance thermal aging, electrical aging and aging under combined stresses.Therefore, it is necessary to analyze the aging mechanism of power cable and to findthe effective way of judging insulation aging.In this thesis, a comparing analysis method is used. Polyethylene, domestic110kV cross-linked polyethylene (produced by Qingdao Han Cable Company), andBorealis110kV cross-linked polyethylene (produced by Borealis Company) aretested under the electrical aging factor. Meanwhile the regulation of characteristicssuch as conduction current, loss factor, and breakdown field strength varying withtime is studied. In addition, infrared spectroscopy and crystallinity of different agingtime insulating materials under thermal aging factor are measured to analyze thechanging in molecular and morphological structure. And then, the aging process andregulation is analyzed at a deep level.In the running process of power equipment, the insulation parts work inevitablyand continuously in the environment that composes various factors, such as thermal, electrical, and mechanical stress. These stresses continue to affect the insulationsystem, and this can lead to the degradation of insulating materials. Thus, the stresseswill eventually lead to early failure of electrical equipment and insulating materials.Therefore, the study on the aging mechanism and criterions of aging of insulatingmaterials is of great significance to prevent accidents. At present, the most commonused method is destructive and defined variables (insulation resistance, loss factors,partial discharge, gas analysis, etc.) method. This paper describes a non-destructivemethod that named absorption current method to determine insulation aging. In thismethod, a step voltage is applied to the insulating materials，and the absorptioncurrent curve is measured to analyze the degree of aging of insulating materials.