Skagerrak (power transmission system)

Skagerrak is the name of a 1,700 MW high-voltage direct current (HVDC) transmission facility between Tjele (Denmark) and Kristiansand (Norway). It is owned and operated by Statnett in Norway, and Energinet in Denmark.[1] The lines connect the hydroelectric-based Norwegian grid and the wind and thermal power-based Danish grid. In operation it enables more renewable energy in the energy mix, and more efficient use of electricity.[2]

Skagerrak
single line diagram of pole skagerrak 3 and 4 from HVDC station Cross-Skagerrak
Location
CountryNorway
Denmark
Coordinates58°15′36″N 7°53′55″E
56°28′44″N 9°34′1″E
General directionnorth–south–north
FromKristiansand (Norway)
Passes throughSkagerrak
ToTjele (Denmark)
Ownership information
OwnerStatnett
Energinet
Construction information
Manufacturer of conductor/cableAlcatel
Nexans
Prysmian
Manufacturer of substationsABB
Commissioned1977
Technical information
Type of currentHVDC
Total length240 km (150 mi)
Power rating1,632 MW (Skagerrak 1–4)
No. of poles4

Technical features

The 240-kilometre (150 mi) Skagerrak 1–3 scheme consists of a 113-kilometre (70 mi) overhead line and a 127-kilometre (79 mi) underwater cable.[1] It has a capacity of 1,050 megawatts (MW). Both land parts in Denmark and in Norway uses overhead lines from the cable landing point to the converter stations.[3] The overhead lines in Denmark are set to be renovated in 2016 for increased lifespan.[4] The towers were originally constructed for four poles, but were rebuilt for three conductors (three poles) when Skagerrak 3 was established. Near Aggersund HVDC Skagerrak crossed Aggersund strait overhead on 70-metre-tall (230 ft) towers with a 470-metre-long (1,540 ft) span, but were later converted to underground cables. The pylons of this span were the tallest electricity pylons of an HVDC line in Europe.

For such a long submarine cable, an AC transmission scheme would not be feasible since too much of the cable's capacity would be consumed by the capacitance of the cable itself, and the power systems in Norway and Jutland are not synchronous.

The transmission has a loss rate of 4%.[5]

The waste heat of the transformers is enough to supply district heating economically for 1,000 homes in nearby towns, but taxes prevent that project.[6] The coming Apple Datacenter (supplied in part by the Skagerrak cables) is expected to work around the tax issue when supplying district heat to Viborg.[7]

Skagerrak 1 and 2

Skagerrak went in service in 1977 as a bipolar HVDC scheme. This facility was built with thyristor valves. When installed this underwater cable was the world's longest and deepest underwater HVDC power cable. The cable, manufactured by Alcatel, is laid in a maximum water depth of 530 metres (1,740 ft).[8]

Both cables have a capacity of 250 MW at 250 kV.[1]

Skagerrak 3

In 1993 the scheme was extended by HVDC Skagerrak 3. Skagerrak 3 is a monopolar line for a voltage of 350 kV with a capacity of 440 MW at 350 kV.[1] In installing Skagerrak 3, the old poles Skagerrak 1 and Skagerrak 2 were converted to monopolar HVDC schemes, which run with opposite polarity to Skagerrak 3.[3]

Skagerrak 4

In November 2009, Statnett and Energinet.dk signed the agreement to construct Skagerrak 4.[9][10] The capacity of Skagerrak 4 is approximately 700 MW. It had been in a test phase since 1 October 2014 and became operational at the end of 2014, when strong winds created negative prices despite the new connection.[11] It was officially inaugurated by Frederik, Crown Prince of Denmark and Haakon, Crown Prince of Norway on 12 March 2015.[12] As for the existing Skagerrak 1-3, the grid connection points are Kristiansand and Tjele. Differently from Skagerrak 1–3, for Skagerrak 4 a cable solution is chosen for the complete route length.[1] The 300 million DKK Prysmian land cable on the Danish side is approximately 90 kilometres (56 mi), while the 137 kilometres (85 mi) subsea cable and the 12 kilometres (7.5 mi) Norwegian land cable is to be made by Nexans for 638 million DKK.[13] Converter stations were built by ABB, as for Skagerrak 1–3.[14] The combined budget is 2.8-3.2 billion DKK.[13][15]

The technology used was VSC, capable of black start. Although thyristor-based converters have a loss of only 0.7%, the IGBTs of VSC get close with a loss of 0.8 to 1%. Skagerrak 1 and 2 previously used Skagerrak 3 as a return cable, but 1 and 2 were again coupled so that Skagerrak 4 can use number 3 for returns.[16] The cable also supplies 110 MW of reserve power.[17] Some of the 24 fiber pairs may be rented for business by telecommunications companies.[18]

Sites
Site Coordinates
Tjele HVDC Static Inverter56°28′44″N 9°34′1″E
Denmark Overhead Electrode Line Terminal56°37′16″N 9°28′32″E
Aggersund Crossing Tower South57°0′0″N 9°18′7″E
Aggersund Crossing Tower North57°0′12″N 9°17′50″E
Danish Cable Terminal57°7′34″N 9°3′58″E
Norway Cable Terminal58°7′45″N 8°10′3″E
Norway Electrode Line Terminal58°10′02″N 8°15′56″E
Norway Electrode Line Branch58°11′10″N 8°9′24″E
Kristiansand HVDC Static Inverter58°15′36″N 7°53′55″E

Waypoints
List of waypoints
Overhead line in Denmark
Underground cable in Denmark
Overhead line in Norway
Electrode line in Norway
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See also

References
  1. "Skagerrak". ABB. Retrieved 2015-09-09.
  2. http://new.abb.com/systems/hvdc/references/skagerrak
  3. "The Skagerrak HVDC Scheme". Bonneville Power Administration. Archived from the original on 2005-08-02. Retrieved 2011-02-13.
  4. http://anlaegsrapport.dk/2015_2016/eltransmission/Sider/Renovering-af-fundamenter-og-omgalvanisering-af-master-paa-HVDC-luftledningen-Bulbjerg-Tjele.aspx
  5. "Norske kabler mister fire prosent av kraften på vei til Danmark". Teknisk Ukeblad. 25 March 2017. Retrieved 10 September 2017.
  6. "#mensviventer blæses spildvarme ud til fuglene". 16 March 2016. Archived from the original on 22 April 2016. Retrieved 26 March 2016.
  7. Daniel McClane (30 July 2015). "Apple fik rådgivning af den danske stat til at betale mindre skat". Version2.
  8. "Submarine power cable to connect Jordan, Egypt". PowerGen Worldwide. PennWell Corporation. 1995-01-01. Retrieved 2011-02-13.
  9. "Kommersiell drift av SK4 utsatt" Statnett, 15 December 2014. Accessed: 16 December 2014.
  10. "Demark, Norway to build fourth interconnector". PowerGen Worldwide. PennWell Corporation. 2009-12-09. Retrieved 2011-02-13.
  11. Bredsdorff, Magnus. Nytårsblæsevejr: Vindmølleejere betaler for at producere strøm (in Danish) Ing.dk, 2 January 2015. Accessed: 2 January 2015.
  12. Lind, Anton. "600 kilometer søkabel skal føre strøm mellem Norge og Danmark" Danmarks Radio, 12 March 2015. Accessed: 13 March 2015.
  13. Mikkelsen, Søren Damsgaard. Billion kroner cables Archived 2011-07-19 at the Wayback Machine Energinet.dk, 7 January 2011. Accessed: 9 January 2011.
  14. "ABB wins $180m order for Norway-Denmark power transmission link". PowerGen Worldwide. PennWell Corporation. 2011-02-11. Retrieved 2011-02-13.
  15. 130 mio. euro for new technology on Skagerrak 4 Archived 2011-02-16 at the Wayback Machine Energinet.dk, 10 February 2011. Accessed: 29 November 2011.
  16. Godske, Bjørn. New cable to Norway secures grid against faults Archived 2012-10-20 at the Wayback Machine (in Danish) Ing.dk, 11 February 2011. Accessed: 11 February 2011.
  17. Offentliggørelse af priser for systemydelser på SK4 Archived 2016-03-03 at the Wayback Machine Energinet.dk, 1 December 2014. Accessed: 25 February 2016.
  18. Zachariassen, Espen. "Statnett bør pålegges å legge fiber i utenlandskablene" Teknisk Ukeblad, 23 October 2013. Accessed: 12 January 2015.
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