Charge transport behavior in XLPE-insulated cables under DC and thermal gradient coupling field considering the effects of non-uniform conductivity

Abstract

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.