Kriegers Flak Grid Connection of Offshore Wind Farm

The Kriegers Flak Offshore Wind Farm’s 600 MW offshore wind turbines will generate green energy corresponding to the energy consumption of 600,000 Danish households.

 

Project background

Energinet has been assigned the task of connection Denmark’s largest offshore Wind Farm at Kriegers Flak in the Baltic Sea to the Danish power grid and the Danish sockets. That is why we’re constructing a so-called grid-connection facility both on and offshore. The facility will transport the power from the offshore wind farm and into the high-voltage grid onshore.

Once completed, the Kriegers Flak Offshore Wind Farm’s 600 MW offshore wind turbines will generate green energy corresponding to the energy consumption of 600,000 households. This is an important contribution to Zealand’s security of supply in the years to come and will at the same time transmit a large amount of green energy into the power grid.

Kriegers Flak plays an important role in Denmark’s objective to become inde-pendent of fossil fuels. Kriegers Flak will be erected a few kilometers from the German offshore wind farm Baltic 2 in the Baltic Sea. Energinet and German 50Hertz Transmission will use this opportunity to connect the two wind farms; creating the world’s first offshore power grid which combines wind energy with the possibility of exchanging power between the two countries. The combined grid solution is granted financial support from the EU.

Technical description

The facility comprises:

• Two offshore transformer platforms
• Two submarine cables, led onshore at Rødvig on Stevns
• Land cable from Rødvig to Bjæverskov substation
• Land cable from Bjæverskov to Ishøj substation
• Land cable between Ishøj substation and Hovegård substation
• Expansion of the existing substation in Bjæverskov
• Rebuild of existing substations in Ishøj, Bjæverskov and Hovegård.

Energinet’s budget for the Kriegers Flak grid connection is DKK 3.5 billion. The facility must be in operation from 31 December 2018.

Start

End

21.05.2014

31.12.2018

Project information

Onshore facility

The onshore facility comprises 95 km land cable, a new substation and expan-sion of existing substations.

Land cables between Rødvig and Bjæverskov

Two parallel 220 kV (200,000 volts) land-cable systems will be laid from Rødvig to Bjæverskov. A land-cable system consists of three conductors laid next to each other in a cable trench.

Rebuild of substations in Bjæverskov, Ishøj and Hovegård

Rebuild of the substations in Bjæverskov, Ishøj and Hovegård are necessary to receive electricity from the offshore wind turbines at Kriegers Flak and transmit it into the existing 400 kV grid. New electrical components will be installed. These components will increase the electrical voltage from the cables’ 220 kV to the grid’s 400 kV.

The new components are similar to and roughly of the same size as the existing components. The rebuilds are all within the existing substation areas.

New substation in Bjæverskov

It is only necessary to expand the substation area in Bjæverskov. The expansion comprises a new substation and a new substation building. The function of the new substation is to regulate the voltage of the long cable to Kriegers Flak as well as direct the output into the power grid. The substation consists of a num-ber of coils to regulate the voltage and circuit breakers for coils and cables. The entire facility occupies approximately 5 hectares.

Land cable between Bjæverskov and Ishøj

The power grid cannot obtain all the power from Kriegers Flak in Bjæverskov, so a 220 kV cable connection is necessary from Bjæverskov to Ishøj.

Reinforcement of the power grid between Ishøj and Hovegård

The power grid is reinforced with a 19 km long 400 kV cable between the sub-station in Ishøj and the substation in Hovegård. The cable is necessary to ensure a stable operation as a result of the increased electricity transmission to Ishøj.

Korean LS Cable & Systems delivers the 220 kV land cables and French Nexans delivers the 440 kV land cables. The Danish company Arkil is responsible for cable burial.

Offshore facility

The offshore facility comprises two offshore transformer platforms and submarine cables.

Offshore transformer platforms

The two offshore transformer platforms collect the power from the offshore wind turbines and increase the electrical voltage from the wind turbines to 220 kV. The platforms are placed approximately 6 km apart. This is due to an area des-ignated for raw material extraction within the offshore wind farm area where wind turbines cannot be placed. 200 MW wind turbines are placed on the west-ern side of the area, and the remaining 400 MW wind turbines are placed on the eastern side.

Each transformer platform consists of a so-called topside and a foundation. Hol-landia constructs the topsides and Scaldis installs them. The foundations are constructed and installed by Iemants and Jan de Nul. The foundations are so-called gravitation foundations. To learn more about this type of foundation and how it is manufactured and installed, click on the PDF below.

Submarine cable

A 220 KV submarine cable is laid between the two transformer platforms. This ensures that part of the power generated by the wind farm can be brought ashore in case one of the transformer platforms is out of operation. A 45 km 220 kV submarine cable is laid from each transformer platform to the shore at Rødvig on Stevns.

The submarine cables are jetted into the seabed to protect them against fishing tools, etc. The submarine cables are manufactured and installed by ABB.

Offshore wind turbines

The offshore wind farm will be constructed and operated by Vattenfall. The con-struction of the wind farm is planned to take place between 2019 and 2021.

Permits and investigations

Permits

The offshore wind farm and the technical facilities that lead the power into the onshore grid have various impacts on the environment. The Danish Authorities must therefore approve the construction of the technical facilities.

On 12 April 2016, the Danish Nature Agency granted Energinet a so-called EIA-permit for the onshore facilities (Environmental Impact Assessment). Click on the link to read the EIA-report (Indsæt link).

The Danish Energy Agency must grant a similar permit for the offshore facilities.

Environmental investigations onshore

The environmental investigations for the onshore facilities were conducted be-tween 2014 and 2015. The impact on the landscape is limited as the cables are buried. The construction of a new transformer station in Bjæverskov will to a certain degree, however, have an impact on the landscape.

Archeological investigations are carried out along the cable route prior to cable burial.

Environmental investigations offshore

The environmental investigations for the offshore facilities were conducted be-tween 2012 and 2015. The offshore facilities can impact commercial fishing activities in the construction period. We will try to minimize this impact through negotiations with the local fishermen. We do not expect the offshore facilities to have other significant environmental impacts.

Archeological investigations of the offshore construction area are also carried out.

Negotiations with landowners

There is no doubt that the land cable will have an impact on the landowners along the cable route. Energinet will take all available precautions to minimize the impact, and the landowners affected by the cable route will be compensated.