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power & industrial
TRANSMISSION LINES
Subsea Cables Tie European Electric Grids More Closely
By Peter Reina
 
Subsea Cables Tie European Electric Grids More Closely
Tennet
Cable faults have put back this month’s planned start-up of the world’s longest subsea power line from Norway to the Netherlands until March. But Norway already plans another line, to Germany, adding to a growing underwater web linking Europe’s grids.

Running between Kvinesdal, Norway, and Eemshaven in the Netherlands, the $860-million NorNed line is roughly twice as long as the former record holder, completed between Australia and Tasmania in 2006.

NorNed’s 450-kV direct-current line includes two 310-kilometer single runs of mass-impregnated-paper-insulated cable from Norway, in up to 410 meters of water. A two-core section completes the shallower southern 270 km.

Dual core prevents magnetic interference with navigation in busy shipping lanes, according to Switzerland-based cable supplier ABB Group, Zurich.

Subsea Cables Tie European Electric Grids More Closely
Tennet

ABB supplied NorNed’s dual core and a total of 154 km of single cable. Its $270-million contract, signed in late 2004, also covers equipping a large AC/DC converter station in each country, built by local contractors. Nexans Norway A.S., Oslo, supplied the remaining, single-core cable.

About half the 40,000 tonnes of cable was in place by October 2006. Early last summer, a local contractor raised the first cable from Norway’s deep seabed and winched it through one of two 1.5-km-long underwater tunnels to shore.

In December, the project hit its first cable fault, about 270 m from the Dutch coast. Soon after that was fixed, tests unearthed a second fault 310-km farther north.

Subsea Cables Tie European Electric Grids More Closely
Tennet

“We have traced the exact location and...we are planning to replace (the cable),” says Carla Verhaaf, a spokeswoman for Dutch grid operator TenneT B.V. With causes of the faults yet to be acknowledged, she says there has not been any discussion of who will eventually pay for the fix.

Launched in late 2004 by TenneT and its Norwegian counterpart Statnett S.F., NorNed will provide the Netherlands with 700 MW of peak-shaving hydropower to complement its thermal plants.

NorNed will also reduce Norway’s over 90% reliance on hydro, says Knut Lockert, a Statnett spokesman. “We believe there is also room for a cable to Germany and we are also considering [one] to Denmark”.

Statnett and German grid operator E.ON Netz have just started a feasibility study of the 700-MW to 1,400-MW Nord.Link line. It will be shorter than NorNed and estimated to cost $1.1 billion to $2.2 billion.

NorNed cable runs roughly twice as far as Australia-Tasmania line.
Tennet
NorNed cable runs roughly twice as far as Australia-Tasmania line.

At same time, a TenneT subsidiary and the U.K.’s National Grid are beginning a 1,000-MW, 260-km line between Isle of Grain, southeast England, and Maasvlakte, near Rotterdam.

Various other European subsea lines are planned. Work has begun on a 420-km cable between mainland Italy and Sardinia, 1,600 m below the Tyrrhenian Sea. And, according to an ABB spokesman, a 75-km subsea cable between Finland and Estonia was completed last month.

 

 

 


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