Abstract
Cross-linked polyethylene is used in extruded HVDC cables and is exposed to electrical and thermal stress. This study examines these insulation systems through conductivity and time-to-breakdown measurements on Rogowski-profiled XLPE samples. Polarization-depolarization current (PDC) measurements on unaged samples were performed at temperatures 40, 60 and 90° C and electric fields from 10 to 60k V/mm. The measured conductivity increases with both temperature and electric field and shows non-ohmic behavior typical of polymer insulation under DC stress. The extracted activation energies range from 1.181 eV at 20kV/mm to 1.02 eV at 60 k V/mm. Among the evaluated models, hopping conduction provides the best agreement with the measurements, with an average hopping distance of 5.6 nm. Time-to-failure tests were performed at 90 °C and 100% relative humidity under DC fields between 55 and 98 kV/mm and fitting the data to the inverse power law model yielded a voltage endurance coefficient of n=6.11.