Space charge modelling in HVDC extruded cable insulation

With the growing interest in the development of HVDC cable technologies, the impact of space charge accumulation inside the polymeric insulation has attracted more attentions and the field distribution across the insulation has become the focus point of research. In this paper, several modifications have been applied on the bipolar charge transport model developed for the cable geometry. Based on many experimental observations, a threshold electric field at which the charge injection takes place was introduced. Considering the practical operation of HVDC cables, the thermal transient effects on space charge behaviors were particularly taken into account. A changing current flow has been applied in the core of a MV size cable, in order to further study the charge dynamics and to anticipate the field distribution within the insulation. The simulation results suggest that the thermal transient can affect the amount of injected charge and the charge movement significantly. The field inversion can only take place with higher temperature and larger temperature gradient, and this can be maintained even with temperature decreasing.