Space Charge Measurement and Modelling in Cross-Linked Polyethylene

Abstract

Cross-linked polyethylene, commercially known as XLPE, is widely used as an insulating material in high voltage cables. However, space charge accumulation under the DC field is one of the most challenging problems in the further development of XLPE insulated cable. Due to the potential electrical degradation ageing process triggered by the accumulated space charges, the IEEE standard 1732 was established for measuring space charge in HVDC extruded cables as the qualification tests. Previous research has revealed that space charge originates from either charge injection at the electrodes or ionization of impurities presenting inside the bulk. In the light of this, this paper aims to simulate the accumulation of space charge in XLPE under DC stress. Space charge measurements have been carried on the fresh and degassed XLPE samples. A modified bipolar charge transport model, by considering the dissociation of impurities, has been employed to simulate the space charge behavior in XLPE. Compared with the experimental observations, the simulation results can reveal appropriate features of hetero charge formation. Both the calculated charge dynamics and field variation are consistent with the experiment results. The restrictions and potential improvements of this preliminary model are also discussed for its future application of XLPE cables.