Novel Diagnostic Method of DC Void Discharge in High Temperature Superconducting Cable Based on Pulse Sequence Analysis

In a high voltage dc (HVDC) high temperature superconducting (HTS) cable composed of polypropylene laminated paper (PPLP), butt-gaps are unavoidable during fabrication, which may lead to formation of voids. When dc voltage higher than partial discharge inception voltage (PDIV) is applied, partial discharge occurs in the void. If void discharge sustains, the electrical ageing of PPLP accelerates, and eventually dielectric breakdown may occur due to the lowering of dielectric strength. Thus, for timely maintenance and repair of HVDC HTS cable, identification technology for void defects is required. However, there is no previous research and technologies for defect identification and insulation diagnosis on HVDC HTS cables. Therefore, in this paper, in order to suggest the insulation diagnosis method for void defects of the HVDC HTS cable based on the pulse sequence analysis (PSA) method, void discharges were measured according to the size of void and magnitude of applied voltage. Also, patterns of the void discharge were obtained using PSA methods and PYTHON program. Experimental results indicate that, although the magnitude, time difference and repetition rate of partial discharge are different depending on the configuration of the void and the applied voltage, but the patterns of void discharge are consistent. Therefore, it is considered that identification and insulation diagnosis for void defects in HVDC HTS cable is possible through the obtained DC void partial discharge patterns.