The space charge accumulation of cross-linked polyethylene is the primary factor leading to the insulation failure of direct current (DC) cables, and the poor understanding of space charge transport behaviors remains as a bottleneck restricting the development of DC energy transmission technology. In this study, an improved bipolar charge transport model, considering the non-uniform conductivity of the insulation at DC voltage and thermal gradient is developed. The charge transport mechanism is revealed based on the space charge and the electric field distribution. The effects of conductivity on space charge and electric field distribution under DC voltage of polarity reversal is discussed as well. The results show that the space charge and the resulted electric field distribution are significantly affected by the temperature and the electric field gradient. A higher conductivity contributes to suppressing space charge accumulation, and a homogenization of electric field is achieved by an appropriate increase in the conductivity. Besides, the increase in the conductivity does not aggravate the space charge accumulation and distort the electric field after the polarity reversal.

交联聚乙烯的空间电荷积累是导致直流电缆绝缘失效的主要因素，对空间电荷传输行为的认识不足仍然是制约直流输电技术发展的瓶颈。在这项研究中，开发了一种改进的双极电荷传输模型，考虑到绝缘在直流电压和热梯度下的非均匀电导率。基于空间电荷和电场分布揭示了电荷传输机制。还讨论了在极性反转的直流电压下电导率对空间电荷和电场分布的影响。结果表明，空间电荷和由此产生的电场分布受温度和电场梯度的影响显着。较高的电导率有助于抑制空间电荷积累，并通过适当增加电导率来实现电场的均匀化。此外，电导率的增加不会加剧空间电荷积累和极性反转后的电场扭曲。