Comparison of two models on simulating electric field in HVDC cable insulation

Space charge accumulation in cable insulation is one of the major technical problems in the further development of HVDC cables. A conductivity model and a bipolar charge transport model are developed to respectively calculate the space charge and electric field distribution in polymeric insulation. In this paper, both models are employed to simulate the field distribution in a medium voltage polymeric cable. Comparisons are made between theoretical and simulation results. The limitations of the conductivity model which is widely used in HVDC cable design are presented, and the results of the bipolar charge transport model are more consistent with the experimental observations. Moreover, transient current in the cable is simulated to anticipate the field distribution within the insulation when subjected to a thermal transient. The results suggest that the thermal transient can affect the space charge and electric field distribution significantly. A field inversion can only take place with higher temperature and larger temperature gradient, and this can be maintained even with temperature decreasing.