Temperature and electric field dependence of charge conduction and accumulation in XLPE based on polarization and depolarization current

Temperature and electric field are important factors affecting space charge accumulation in high voltage dc (HVDC) cable insulation. Charge conduction and accumulation in XLPE have been studied by correlating the polarization and depolarization processes. The experimental results indicate that the steady current of XLPE increases about 2 or 3 orders with the increasing temperature from 25 °C to 90 °C, and the stronger electric field, the less the increased amplitudes. The trap level in XLPE stressed by different electric fields and temperatures have a tiny change from 0.89 eV to 1.15 eV. Besides, there exists an inflection temperature of charge accumulation in XLPE, around 50 °C∼ 60 °C. At the room temperature, the trapped charges are difficult to release from the traps, and these homo-charges near the electrode can depress the further injection of charges. With the increase of temperature, part of trapped charges near the interface will gradually migrate towards the bulk of the material, and more charges are injected. When the temperature exceeds around 50 °C, the molecular movement is accelerated which can dramatically enhance the hopping probability of charges between the adjacent traps, and little accumulated charges are left.