Influence of Polarity Reversal Period and Temperature Gradient on Space Charge Evolution and Electric Field Distribution in HVDC Extruded Cable

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.