2008-09-05 - ABB’s high-voltage power cable factory in Sweden is one of the most modern cable factories in the world, and has supplied dozens of power projects around the world, including the 580-km long link that now connects the power grids of Norway and the Netherlands. NorNed, the world’s longest submarine power link, passed operational tests at the end of June.
By ABB Communications
Spread over a 36,000 square-meter site in the historic Swedish port and UNESCO World Heritage site of Karlskrona, ABB’s high-voltage cable factory is about as close to the historical and technological center of the power cable industry as one can be.
“Cable production is a highly complex process that requires great skill, knowledge and expertise,” says Hans-Åke Jönsson, head of ABB’s high-voltage cable business and site manager of the Karlskrona factory.
A cutaway view of the 580-km long HVDC submarine cable that now connects the power grids of Norway and the Netherlands. The link weighs 47,000 tonnes in total and was laid in eight sections which took more than three years to produce and install. It passed operational tests in June of this year.Arranged before him on a large table are cross-sections of some of the factory’s many pioneering cable installations, evidence of the prominent role ABB and the Karlskrona factory have played in the evolution of power transmission in the past half century.
They include the world’s first high-voltage direct current (HVDC) and cross-linked polyethylene (XLPE) high-voltage submarine cables, and the world’s longest underground and submarine cable installations – Murraylink in Australia and NorNed in the North Sea.
Supported by a sister manufacturing facility in Russia and a cable accessories factory in Sweden, ABB’s capability at Karlskrona encompasses the entire supply chain - from system design to manufacture, installation, commissioning and service.
The Karlskrona factory consists of two production lines, one for paper-insulated and the other for extruded XLPE and HVDC Light cables. It has its own deepwater harbor and research laboratories and one of the best views of the Baltic from the site’s giant extrusion tower.
Spooling the final batch of the NorNed cable onto one of three giant turntables. It takes 9-10 days to spool the cable onto the turntable. Each turntable has a capacity of 7,000 tons and 150 kilometers of cable. A new turntable will be installed in 2008 as part of the factory’s extensive investment program. The NorNed connection is a joint project between the Norwegian and the Dutch transmission system operators (TSOs), Statnett and TenneT.
It comprises a 580-km long, high-voltage direct current (HVDC) submarine cable with converter stations at each end connected to the respective grids in each country. The system links the Norwegian and Dutch power networks so each can trade and transmit electricity to the other. This strengthens their respective grids and helps stabilize energy prices in both countries.
The NorNed link passed operational testing on June 27. The link's cable has a 700-megawatt capacity, and its completion adds another piece to the power transmission jigsaw in Europe which will eventually create a single electricity market on the continent - the European Union's Trans-European Network initiative.
In December 2006, Finnish and Baltic utilities innaugurated Estlink, (also built by ABB, this time using about 100 kms of HVDC Light power cable), enabling power exchanges between Latvia, Estonia, Lithuania and Nordel, a collaboration between the grid operators in Sweden, Norway, Denmark, Finland and Iceland.
Manufacturing a 580-kilometer cable like NorNed is a long and demanding process.
Copper strands are braided to make the conductor, the cable's core.
NorNed provided ABB with an additional challenge in that it is the first double cable for power transmission purposes ever manufactured by ABB (see image above).
“The customer received approval for the design several years ago but their cable supplier was unable to meet the specifications,” says Jönsson. “They came to ABB, and we delivered the final batch last Fall. It was a very successful project.”
Manufacturing HVDC cable for systems like NorNed is a complex series of steps that begin with stranding the copper conductor. The conductor is then lapped with paper, impregnated with oil for many months and encased in a lead sheath.
The sheath is then covered twice in a layer of bitumen and steel wire armoring to give it the strength to withstand impact from ship’s anchors and provide at least 40 years of maintenance-free service.
“It takes about nine months to manufacture a batch of cable like NorNed, and about 30 months to complete the entire order,” says Jönsson.
Binding the two NorNed cables into a single piece: two layers of bitumen and steel wire armoring give the cable the strength to last at least 40 years. For extruded cables like XLPE and HVDC Light, the conductor is passed slowly through an extrusion tower, where insulating and conducting material are applied.
The cable passes down through the tower into an underground shaft for cooling and relaxation.
A metallic screen and tough laminated sheath are then applied to protect the cable from mechanical impact and corrosion.
Extruded cables are increasingly preferred to their oil-based, paper-insulated alternatives. They are leaner and more flexible, offer very good performance, lower power losses, and are environmentally friendly (no risk of oil spills).
In the factory’s research and development center, another pioneering cable innovation is undergoing regulatory 12-month tests to simulate several years of field operation and comply with the necessary international standards.
“The 320 kV HVDC Light cable more than doubles the existing 150 kV that was used in such milestone installations as Estlink, Cross Sound and Murraylink, says Jönsson. “The entire cable - components, joints and terminations – will be ready for commercial release in 2008.”