Calculation of Electric Fields in HVDC Cables: Comparison of Different Models

This paper presents a comparison of different models used for calculations of electric field distributions in HVDC cable insulation. Calculated electric field and space charge distributions for a loaded 320 kV HVDC cable are compared with the experimental characteristics reported in the literature. Additionally, for selected models, a sensitivity of the results to variations of the model parameters is analyzed. It is noticed that the calculations utilizing the empirical expressions for the field and temperature dependent electric conductivities (Le., macroscopic approach) allowed for predicting so-called field inversion phenomena under DC stresses. It is found, however, that such models are not capable of predicting the magnitudes of the maximum field stress and polarity of the accumulated space charges accurately. Models based on bipolar charge transport (i.e., microscopic approach) in addition to the effects described by the macroscopic models, predict the experimentally observed accumulation of homo- and hetero-charge in the insulation reasonably well. It is concluded that the microscopic approach has been used with proper descriptions of the rates and parameters of physical processes of the transport, generation and losses of charged species in the bulk of the insulation, as well as of its interfaces, provides convincing electric field estimations for HVDC cables. Because of the uncertainty in model parameters, the accuracy of DC field calculations is less than the high accuracy of AC calculations for HVAC cables that we are used to.