Subsea cable works begin for DolWin6

4C Offshore | Tom Russell
By: 29/06/2021 TenneT

TenneT has started laying cables in shallow water and offshore areas for the DolWin6 offshore grid connection project. Clearance of twelve identified ammunition from the past two world wars along the sea route was completed in last month and the laying of the submarine cable section is now primed to begin.

The cable laying planned for 2021 is divided into two sections. Around 39 km of cable section in total is to be installed offshore; around 6.5 km in shallow water and 33 km offshore. Cable laying work on and north of Norderney will take place between the end of June and mid-September 2021

In 2017 and 2018, TenneT carried out horizontal bores up to 1,100 meters in length (HDD method) on Norderney. Protective tubes were drawn into these boreholes. For the work that will now take place in 2021, TenneT will pull the high-voltage cable into the "North Cable Protection Pipe" and connect it to the Watt cable, which was already pulled into the South Cable Protection Pipe in 2020, by means of sleeves.

At the same time, a further cable section is being laid in the north of Norderney using flushing technology up to the 12 meter waterline in shallow water. A standing flushing device, which is located on a cable-laying pontoon, is used for this work. The cables are inserted from this pontoon into the flushing device and laid step by step through the slow movement of the pontoon into the seabed.

The second section comprises the offshore cable laying work from the 12 meter waterline to the future location of the DolWin kappa offshore converter station. During this work, the cable is temporarily placed on the seabed and then flushed into the ground with the help of a flushing device. In the shallow water area, the submarine cable end is connected to the shallow water cable with sleeves. The submarine cable will be pulled into the offshore converter platform in 2022.

The project's offshore converter platform, DolWin kappa, is currently being built in a shipyard in Cárdiz (Spain). It will be shipped to the North Sea in 2022. It will be used to transmit energy generated by nearby offshore wind farms to the onshore grid.

For more information on subsea cable projects worldwide, click here