The Performance of Strippable and Bonded Screened Medium-Voltage XLPE-Insulated Cables Under Long-Term Accelerated Aging

Abstract

XLPE high-voltage underground cables are being extensively used in Arabian Gulf countries. Most of these cables are being manufactured locally. Although XLPE has excellent dielectric characteristics, extensive premature failures have been reported by the local power utilities. The main causes of such premature failures are related to manufacturing defects and insulation degradation mainly caused by water treeing phenomena. In this research work, five types of 15-kV, XLPE-insulated cables were subjected to accelerated aging under simultaneous electrical, thermal, and environmental stresses for periods of 60, 120, and 180 days. After each aging period, partial-discharge (PD), mechanical properties, ac dielectric strength and the extent of degradation due to water treeing of these cables were measured. The results show that PD and mechanical properties show just little variations whereas the ac-retained dielectric strength decreases rapidly in the first 60 days after which the rate of its decrease retards. Correlations are established between the retained dielectric strength and the lengths of the longest water trees. Pros and cons of the insulating materials that are used as well as the role of strippable and bonded semiconducting screens are also discussed