Space Charge Dynamics in HVDC Cable Insulation under Transient Voltages

This study investigates the dynamics of space charge and the evolution of the electric field within HVDC cable insulation when subjected to DC superimposed with impulse voltages. A one-dimensional electrothermal coupled simulation model of a coaxial cable is developed based on an enhanced bipolar charge transport (BCT) model. Simulation results reveal that homopolar impulse significantly intensifies the electric field, thereby facilitating homocharge migration and injection, which results in an increased positive charge density within the insulation. In contrast, the densities of negative and heteropolar charges near the outer interface decrease as a result of enhanced charge recombination. The charge transport behavior near the inner interface becomes complex under heteropolar impulse stress superposition, principally owing to the periodic reversal of the electric field's polarity. During the polarity reversal, both alterations in types of charge injection/extraction and the reversal of charge migration direction contribute to the decrease in density of positive charge near the inner interface. Conversely, since field polarity near the outer interface remains stable, the charge dynamics resemble those under DC stress. The reduction in field strength caused by the heteropolar impulse stress leads to a relatively slight variation in charge density near the outer interface.