Partial Discharge Characteristics from Internal Defects in High Voltage Cable Joints

Cable joints are critical weak points in high-voltage insulation systems, prone to degradation caused by structural irregularities and installation flaws. Partial discharge (PD) often appears as an early indicator of insulation weakening. Among internal defects, protrusions and insulation incisions play key roles in initiating PD activity. In this study, partial discharge behavior in XLPE-insulated cable joints fabricated using the taped joint technique is experimentally investigated by intentionally introducing protrusion and incision defects and applying AC test voltages at multiple levels. Prior to PD measurement, the insulation condition is evaluated using indices such as polarization and dielectric absorption to assess the initial degradation level. The main observables include the PD inception voltage (PDIV) and the corresponding patterns revealed in PRPD. The results show distinct behaviors: protrusion defects, with a PDIV of 12.54 kV, produce broad Phase-Resolved Partial Discharge (PRPD) distributions across wide phase ranges, particularly accentuated during the half-cycle where electric field concentration is highest. This highlights how sharp protruding tips intensify local electric fields and promote discharge activity. In contrast, insulation incision defects, with a PDIV of 13.73 kV, generate tightly clustered PRPD patterns, with pulses confined to narrow phase windows and exhibiting higher magnitudes. This reflects localized enhancement of electric stress around the cut edges. These contrasting discharge signatures reveal how defect geometry dictates local field distortion and hence discharge behavior, offering a pathway to differentiate between protrusion and incision defect in cable joints.