Dielectric diagnosis of 24KV XLPE cable using polarization and depolarization current, conventional partial discharge measurements and high frequency current measurement

Abstract

Medium voltage power cables are an important element of electric power distribution. Most of cable failures occurring in XLPE insulation and cable accessories are due to insulation failure. This research work represents the dielectric investigation of 12/20(24) kV XLPE power cables including cable joints by using polarization and depolarization current (PDC) measurement, conventional partial discharge measurement according to IEC 60270, and high frequency current measurement measured by high frequency current transformer (HFCT). In this research work, six case studies, case 1: PE sheath damaged, case 2: semi-conducting layer damaged, case 3: void defect in extruded cable, case 4: void defect in extruded cable at cable joint, case 5: semiconductive contaminant at cable joint, and case 6: conductive contaminant at cable joint, were investigated. The test results showed that two basic properties, polarization and depolarization current, of cable insulation can be utilized for classification of cables with joint problems. The defects in extruded cable and cable joint can be identified by the PDC shapes. However, to clarify the problems occurring at the cables by conventional PD measurement and HFCT measurement was performed. Moreover, it was found that the sensitivity of HFCT was clearly lower than conventional tool.