In 2014, the national transmission system operator in Norway, Statnett, commissioned a new 13-km (8-mile) 420-kV submarine cable interconnection across the Oslo Fjord to replace a time-expired 12-km (7.5-mile) 420-kV interconnection comprising six 420-kV single-core fluid-filled (SCFF) cables in service since 1981. This interconnection is part of an important circuit in the Norwegian grid, with the demand for more transmission capacity was one of the reasons for installing the new cables.
The project consisted of:
- Pre-removal survey
- Oil draining from cable ends
- Mobilization for marine operations
- Removal of concrete culvert covers
- Removal of cable joint protection mattresses and joints
- Cutting and sealing of cables outside the four landfalls
- Cable retrieval
- Cable disposal
- Removal of the oil-pressure system and termination buildings, in parallel with the maritime scope
- Recycling of disposed system parts and cables.
Following are images of the process. To read about the full project, see "Statnett's Removal of Fluid-Filled Submarine Cables," first published in the September issue of T&D World.