MV overhead lines using XLPE covered conductors. Scandinavian experience and NORWEB developments

After 15 years of experience with MV covered overhead line systems in Scandinavia, components, system and installation practices have reached a state of established technology. The system offers phase clearance of only 50 cm and the ability to allow grounded objects to touch the line and phases to touch each other, without any tripping or customer outage. A substantial improvement in service reliability and a reduction in life cycle costs, compared to bare lines, is achieved. The aluminium alloy conductor is covered with black UV-resistant XLPE and filled with grease, to provide corrosion protection and longitudinal watertightness. Arcing guides are applied at insulator tops, to protect the line from arcing damages. Methods for determining the necessary frequency of arcing guides have been developed, based on probabilistic approaches. NORWEB plc has adapted the Norwegian covered line concept, realising it through test sites and by defining a NORWEB design for their further development in accordance with the UK Electricity Supply Regulations of 1988