Abstract
During the operation of HVDC extruded cables, voltage polarity reversal (VPR) is considered one of the most severe conditions for cable insulation. In this paper, a bipolar charge transport model developed for cylindrical geometry is improved by introducing ionic carriers from impurity dissociation for the simulation of space charge and electric field in an HVDC extruded cable with thick polymeric insulation under VPR, and the construction of the geometric model is based on a practical 160 kV DC polymeric cable. The influence of polarity reversal period (PRP) and temperature gradient (TG), formed by the load current flowing through the conductor, on the space charge evolution and the electric field distribution are investigated. The mechanisms of the charge dynamics and the field distortion affected by the PRP and the TG are also discussed. The results show that under TG, the maximum transient field appears near the interface between the conductor shield and insulation in the early stage of complete VPR. In addition, the longer the PRP, the more serious the maximum transient field distortion. Moreover, an increase in TG intensifies the maximum field distortion under steady and transient states due to the enhancement of heterocharge accumulation.
Highlights
High-voltage direct-current (HVDC) transmission technology is widely used in longdistance and large-capacity transmission and regional power grids interconnection [1]
With the polarity reversal (PR) process, the cable insulation is subjected to a high transient field caused by the superimposition of the applied DC field and the distorted field induced by space charge
The influence of the temperature gradient (TG) formed by high load current on the charge dynamics and the field distribution under the voltage polarity reversal (VPR) becomes necessary for a reliable assessment of the cable insulation performance
Summary
High-voltage direct-current (HVDC) transmission technology is widely used in longdistance and large-capacity transmission and regional power grids interconnection [1]. With the expansion of transmission distance, the increase in voltage level and the enlargement of transmission capacity require a stable operation of the HVDC extruded cable, with a high current-carrying capacity In this case, the influence of the TG formed by high load current on the charge dynamics and the field distribution under the VPR becomes necessary for a reliable assessment of the cable insulation performance. The existing simulations based on the BCT model mainly focus on the insulation under an applied DC voltage with a unipolarity, while little attention has been paid to the effect of VPR on the charge accumulation and the field distribution, especially during the operation of a practical HVDC extruded cable.
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