Abstract
Mass Impregnated PPLP cable, which is applied to various high-voltage direct current (HVDC) projects due to its excellent dielectric and temperature properties, has a problem wherein voids are formed inside the butt-gap due to cavitation. However, there has been no previous research into technology for void defect identification and insulation diagnosis on HVDC MI-PPLP cables. In this paper, to propose an insulation diagnosis method for void defects in HVDC MI-PPLP cable, the direct current (DC) void discharge patterns were analyzed according to the specimen temperature and the magnitude of applied voltage using the pulse sequence analysis method. In addition, to confirm the pre-symptoms of dielectric breakdown in MI-PPLP cable due to DC void discharge, partial discharge patterns were analyzed continuously until dielectric breakdown occurred. From the experimental results, DC void discharge patterns of the same shape were obtained regardless of the specimen temperature and the magnitude of applied voltage. In addition, it was confirmed that new insulation aging patterns were generated as electrical and thermal aging occurred due to the continuous DC void discharge. Therefore, it is demonstrated that identification and insulation diagnosis of void defects in HVDC MI-PPLP cable is possible through the obtained DC void discharge and insulation aging patterns.
Highlights
To analyze the direct current (DC) void discharge characteristics according to temperature, the temperatures of the specimen were set at 55 ◦ C, 65 ◦ C, and 75 ◦ C, based on the operating temperature of the high-voltage direct current (HVDC) mass impregnated (MI)-PPLP cable
Based on the experimental results, to measure the void discharge according to the magnitude of the applied voltage, the applied voltages were set as 25 kV, 30 kV, and 35 kV, which are between the lowest value of breakdown voltage (BDV) and the highest value of partial discharge inception voltage (PDIV)
In order to propose an insulation diagnosis method for void defects in HVDC MI-polypropylene laminated paper (MI-PPLP) cable, DC void discharge patterns were obtained according to the magnitude of applied voltage and temperature of the specimen
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Void defects formed in the butt-gap of HVDC MI-PPLP cables greatly affect the insulation reliability of the cables. To diagnose defects in the insulation of HVDC MI-PPLP cables, it is necessary to study the direct current (DC) void discharge and the pre-symptoms of dielectric breakdown. AC partial discharge characteristics of each defect have been studied sufficiently, and are currently used for insulation diagnosis of Highvoltage alternating current (HVAC) cables [28,29,30,31,32]. The patterns of DC void discharge according to the temperature and applied voltage of the specimen were analyzed to develop an insulation diagnosis method for void defects in HVDC MI-PPLP cables. Based on the patterns of DC void discharge, the pre-symptoms of dielectric breakdown due to void defects in the MI-PPLP cable were confirmed
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