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 cables with different insulation thicknesses. The modified bipolar electronic-ionic charge transport (BEICT) model for full-size cables, which considers both space charges generated by interface injection and ion dissociation, is established based on the finite element analysis (FEA) method. The results show that when a voltage of +500 kV is applied on the conductor, with the increase of temperature gradient (
$\Delta \text{T}$
), the injection of homocharge near the inner semi-conductive layer accelerates, while the heteropolar ionic charge dominates on the low-temperature side. When
$\Delta \text{T}$
reaches 30 °C, the
${E}_{{\text {max}}}$
of the electric field is increased by about 53% compared with 27.85 kV/mm when
$\Delta \text{T}$
= 10 °C; and the
${E}_{\text {max}}$
is located near the outer semi-conductive layer whether under the positive and negative polarities, which are 42.69 and 64.78 kV/mm, respectively. The significant polarity effect is owing to the differences between the injection and migration parameters of positive and negative carriers; furthermore, the increase in thickness will raise the
$\Delta \text{T}$
within the insulation, aggravating the electric field uneven distribution. It is concluded an appropriate reduction of insulation thickness can effectively mitigate the electric field distortion problem caused by
$\Delta \text{T}$
in ±500 kV HVDC cables.