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The stabilization of cross-linked polyethylene (XLPE) cables is crucial to the safe working of power systems. In order to investigate the aging characteristics of cable insulation in the process of operation, 10 kV XLPE cables were electrically-thermally aged at an AC voltage of 26.1 kV and three temperatures: 103°C, 114°C, and 135°C. Cable samples at five aging stages were cut into slices and tested to determine their mechanical, physicochemical properties and dielectric strength. The changes in these properties were analyzed in terms of aging time. The mechanical strength and oxidation induction time have the same changing trend of decrease, because the chemical bonds of the cable insulation material are fractured when the XLPE cable is aged. The AC space charge presented a trend of gradual accumulation with aging time. The breakdown field strength after AC voltage application decreases monotonically with aging time, which could be a characteristic index to evaluate the degradation degree of the cable insulation. This research contributes to the comprehension of degradation mechanism and discovery of aging assessment criteria, which is of great significance in assessments of insulation properties and fault detection on 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]

The space charge features of cable insulation peelings are investigated under ac stress as a function of electrical aging imposed previously on cable sections. The investigated samples are 230-?m-thick peelings of crosslinked polyethylene cable insulation. The space charge profiles are resolved into 32 symmetric phase angles under 50 Hz ac stress. The space charge density in the phase angle of maximum applied field is the largest, as expected, but does not change visibly as a function of aging time. A method that involves averaging space charge in all phases is proposed. The all-phase averaged space charge, which appears in essence as stationary charge, exhibits an obvious increasing trend with stressing time. The aging characteristics of space charge formed under ac stress are investigated considering the all-phase averaged profiles, and the mechanical properties and degree of crosslinking are characterized as complementary methods. The change in the accumulation of space charge under ac stress follows opposite trends unlike the degree of crosslinking, which means that space charge under ac stress has a close relationship with defect concentration in cable insulation. This research contributes to the understanding of space charge features under ac conditions and the understanding of the ac aging principle of cable insulation. [ABSTRACT FROM PUBLISHER]