Polarization and Depolarization Current Characteristics of Cables at Different Water Immersion Stages

To address the insulation degradation caused by moisture intrusion due to damage to the outer sheath of power cables, this study systematically analyzed the charge transport characteristics of XLPE cables at different water immersion stages using polarization/depolarization current (PDC) measurements. An evaluation method for assessing water immersion levels was proposed based on conductivity, charge density, and charge mobility. Experiments were conducted on commercial 10 kV XLPE cable samples subjected to accelerated water immersion for durations ranging from 0 to 30 days. PDC data were collected via a custom-built three-electrode measurement platform. The results indicated that with increasing immersion time, the decay rate of polarization/depolarization currents slowed, the steady-state current amplitude rose significantly, and the DC conductivity increased from 1.86 × 10−17 S/m to 2.70 × 10−15 S/m—a nearly two-order-of-magnitude increase. The Pearson correlation coefficient between charge mobility and immersion time reached 0.96, indicating a strong positive correlation. Additional tests on XLPE insulation slices showed a rapid rise in conductivity during early immersion, a decrease in breakdown voltage from 93.64 kV to 66.70 kV, and enhanced space charge accumulation under prolonged immersion and higher electric fields. The proposed dual-parameter criterion (conductivity and charge mobility) effectively distinguishes between early and advanced stages of cable water immersion, offering a practical approach for non-destructive assessment of insulation conditions and early detection of moisture intrusion, with significant potential for application in predictive maintenance and insulation diagnostics.