Mapping Nonlinear Dielectric Response in Thermally Aged XLPE Cables Across Voltage, Frequency, and Temperature

Thermal aging alters the voltage-dependent dielectric response of cross-linked polyethylene (XLPE) cable insulation. Characterizing the temperature dependence of this response is necessary for comparing insulation measurements obtained under different thermal conditions. A high-voltage variable-frequency measurement circuit was established to investigate 10 kV XLPE cables thermally aged at 150 °C for 0–42 d. Voltage–current measurements covered peak total applied voltages of 100–2000 V and frequencies of 0.01–1000 Hz at 30 and 90 °C. Polarization-derived resistance, differential scanning calorimetry, and capacitance measurements at 1 V provided complementary references for insulation aging. Resistance decreased with aging, whereas the capacitance response depended on temperature and provided limited separation between some aging stages. The voltage dependence of admittance was most pronounced at 0.01–0.1 Hz. At 0.01 Hz, the normalized complex-admittance increment increased and then decreased with aging, reaching maxima of 5.5 and 4.0 at 30 and 90 °C, respectively. The characteristic boundary frequency and transition voltage generally increased with aging and were lower at 90 °C than at 30 °C. These shifts differed from the nonmonotonic evolution of nonlinear strength. At 0.01 Hz, conductance exhibited larger normalized voltage-dependent deviations than susceptance. The results distinguish changes in nonlinear strength from shifts in the frequency extent and voltage transition of the response. Joint analysis of these characteristics and the admittance components provides complementary descriptors of aging-related dielectric changes at different test temperatures.