Insulation Status Assessment of Underground Cable Joint based on Fractal Theory

• Main Authors: Wei-Sheng, Cai, 蔡偉聖
• Other Authors: Ruay-Nan Wu
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/08903387204111152291

碩士 === 國立臺灣科技大學 === 電機工程系 === 100 === In the recent years, the transmission way is changed from overhead line circuit to underground for power companies in the urban distribution systems. In the underground cables, the cable joints may be weak points for breakdown as a result of the construction of the artificial defection. Therefore, exploring the underground cable joint insulation state is the most important issue. In this thesis, the cable joint is used as the test material in the partial discharge test and the artificial defect is produced in joints deliberately, and then applying high voltage to the test material until the insulation breakdown, during the trial term, the partial discharged data is retrieved by data captured card in the fixed time and by using filtering, simplification, conversion to extract the characteristic parameters and phase resolve pattern. Finally, the fractal dimension value is obtained by calculation of the phase resolve pattern for each pattern, and compared to each other characteristic parameters, by the calculation of the result mentioned above. The discharge sum and discharge number are the similar diameter trend, furthermore, the fractal dimension is limited to between 2 and 3. Finally, the first-order fitting error is calculated, and the differential thresholds are computed by the differential rates of the averaged error. Furthermore, the more precise dimension values among those tests in each condition are taken out. When dimension values are close to 2.25 or exceed, it will end in the insulating deterioration. Therefore, the appropriate warning can effectively reduce the accident occurance at this time.