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The space charge dynamic behavior and accumulation are important contributions to the formation of electrical trees, as recognized by cross-linked polyethylene (XLPE) cable insulation under alternating current electric stress. In this article, in order to investigate the reasons for the charge accumulation phenomenon revealed by experiments under ac stress, a bipolar space charge transport model with symmetrical and asymmetrical parameters is built under ac stress. The charge accumulation mechanism is analyzed based on the variation of space charge density with different voltage application time and voltage phase. The effects of each major physical parameter are simulated and analyzed, respectively. The results show that there is no obvious space charge accumulation with the transport model under symmetrical physical parameters. However, asymmetrical parameters in the transport model result in different motions between positive and negative charges, which greatly enhances the charge accumulation. Each main parameter has an influence on charge accumulation in different perspectives and extents. The applicability of the simulation model with asymmetrical parameters is evaluated by comparing experiment and simulation results. This study contributes to the understanding of space charge generation mechanism under ac voltage and serves as a basis for improving the stability of XLPE electric power cables. [ABSTRACT FROM AUTHOR]

To study the effect of semiconductive (SC) material on space charge accumulation in cable accessories, an accelerated aging of cable samples with cable accessories was carried out in the laboratory. The experimental results show accumulation of space charge in the cable insulation covered by a stress cone, whereas the space charge was negligible in the region wrapped by the accessory-reinforced insulation as well as regions not in contact with the accessory. With increased aging time, the space charge density gradually increased, and the axial distribution gradually extended. A comparative experiment on cable insulation slices was carried out using silicone rubber and EVA SC material as the upper electrodes to determine the cause of the space charge accumulation. The results showed that a large quantity of heteropolar charges accumulated near the silicone rubber SC upper electrode, whereas the charges near the EVA SC electrode were negligible. It was concluded that due to the weak charge conducting ability of the silicone rubber SC material used as the electrode, space charges cannot escape from the stress cone and thus accumulate on the outside of the cable insulation at the stress cone position. This paper shows that the SC material used in cable accessories plays an important role in space charge accumulation. [ABSTRACT FROM AUTHOR]

A pulsed electro-acoustic equipment system was devised to measure the space charge of a power cable under 50 Hz AC stress and a high temperature gradient by adopting a new phase-matching method. Space charge profiles were recorded on a 10 kV cable with cross-linked polyethylene insulation. The AC period was resolved in 32 phase angles, while the cable underwent electrical-thermal aging for 16 days. Two types of space charge were discovered, termed periodic charge and stationary charge according to whether they change with AC phases. The periodic charge was not determined to develop over time, while the stationary charge increased gradually as the cable aged. A method called the all-phase average was employed to clearly recognize the stationary charge. An interesting phenomenon was discovered upon attempting to regenerate space charge in the cable after the charge was eliminated. The stationary charge regeneration speed was found to depend strongly on temperature and electrical field. This paper provides a theoretical interpretation for the generation of periodic charge and stationary charge, as well as the dependence of charge regeneration on temperature and electrical field. A new model is raised to account for the generation of stationary charge, explaining how residual charge in one sine period undergoes different charge migration processes around a tip defect between negative and positive periods. [ABSTRACT FROM AUTHOR]