Temperature-Gradient-Dependent Space Charge and Electric Field Evolutions of ±500 kV HVDC Cables With Different Thicknesses

This article focuses on temperature-gradient-dependent space charge and electric field evolutions of +/- 500 kV high voltage direct current (HVDC) extruded cableswith different insulation thicknesses. The modified bipolarelectronic-ionic charge transport (BEICT) model for full-size cables, which considers both space charges generatedby interface injection and ion dissociation, is establishedbased on the finite element analysis (FEA) method. Theresults show that when a voltage of+500 kV is appliedon the conductor, with the increase of temperature gra-dient (Delta T), the injection of homocharge near the innersemi-conductive layer accelerates, while the heteropo-lar ionic charge dominates on the low-temperature side.When Delta T reaches 30degree celsius, theE(max)of the electric fieldis increased by about 53% compared with 27.85 kV/mmwhen Delta T=10degree celsius; and theE(max)is located near theouter semi-conductive layer whether under the positiveand negative polarities, which are 42.69 and 64.78 kV/mm,respectively. The significant polarity effect is owing to thedifferences between the injection and migration parametersof positive and negative carriers; furthermore, the increasein thickness will raise the Delta T within the insulation, aggra-vating the electric field uneven distribution. It is concludedan appropriate reduction of insulation thickness can effec-tively mitigate the electric field distortion problem causedby1T in +/- 500 kV HVDC cables