Space Charge and Electric Field Dependent on Polarity Reversal of HVDC Cable Insulation
Zhonglei Li, Zhong Zheng, You Wu, Boxue Du
Abstract
This article focuses on the effect of the polarity reversal on the space charge behavior and electric field evolution of ±500-kV HVDC cables under different temperature gradients. A modified bipolar electronic-ionic charge transport (BEICT) model of XLPE insulation considering the dissociation of impurities is established for full-sized cables. The results demonstrate that the increase in temperature gradient accelerates the injection and migration of homocharge in the vicinity of the inner semi-conductive layer under dc voltage, which leads to a higher electric field immediately after polarity reversal occurring on the interior side of the insulation. As the temperature gradient increases from 0 °C to 30 °C, the rate of charge variation increases more than tenfold, and the maximum electric field value increases by 15.8% during polarity reversal. Prolonging the polarity reversal period (PRP) results in the accumulation of negative space charge on the inner side of the insulation during polarity reversal, leading to a weakening of the maximum electric field. When the PRP increases from 300 ms to 120 s, the maximum electric field decreases by 9.8%. Moreover, a relaxation period of 600 s when the voltage drops to 0 kV will further reduce the maximum electric field by 16.1%. It is concluded that electron injection and carrier recombination dominate the charge behaviors on the interior side of the insulation during the polarity reversal, which are the primary factors affecting the electric field distortion.