Temperature-Gradient-Dependent Space Charge and Electric Field Evolutions of ±500 kV HVDC Cables With Different Thicknesses
Zhonglei Li, You Wu, Zhong Zheng, Boxue Du
Abstract
This paper focuses on temperature-gradient-dependent space charge and electric field evolutions of ± 500 kV 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 (ΔT), the injection of homocharge near the inner semi-conductive layer accelerates, while the heteropolar ionic charge dominates on the low-temperature side. When ΔT reaches 30 °C, the Emax of the electric field is increased by about 53 % compared with 27.85 kV/mm when ΔT = 10 °C. And the Emax 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 ΔT 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 ΔT in ± 500 kV HVDC cables.