Siemens-Dragados Offshore consortium to build BorWin5 substations

Transmission system operator TenneT has awarded the consortium of Siemens AG and Dragados Offshore SA with a contract to build onshore and offshore converter stations for the 900 MW BorWin5 grid connection.

At 230 kilometres, BorWin5 will be the longest offshore direct current connection to date, scheduled for commissioning in 2025.

BorWin5 is the 15th offshore grid connection system implemented by TenneT in the German North Sea, the twelfth of which is direct current connection.

In addition, BorWin5 is the second project after DolWin5 in which the wind turbines are connected directly to the BorWin epsilon offshore platform via 66-kilovolt three-phase cables. This means that the transformer stations previously required in every wind farm are no longer necessary, TenneT said.

In addition, 155 kV three-phase cables are no longer required to connect the TenneT offshore platform to that of the wind farm.

After conversion, TenneT will use a 230-kilometre high-voltage direct current cable to transmit the electricity to the Garrel / Ost converter station on land using low-loss direct current technology.

Here, the direct current will be converted back into the three-phase current and fed into the extra-high voltage network.

BorWin5 is the fourth offshore grid connection that TenneT has implemented using high-voltage direct current transmission technology off the coast of the Borkum island in the German North Sea. This grid link will connect the EnBW He Dreiht wind farm to the German transmission network.

“With the award of BorWin5, we are proceeding with the continuous cost reduction in the construction of offshore grid connection systems,” Tim Meyerjürgens, TenneT’s COO, said.

”Compared to the predecessor project DolWin5, we were again able to achieve a significant cost reduction for the converter stations. One reason is that for BorWin5 the smart platform concept is being used for the first time. This not only keeps the costs for the platform construction manageable, but also allows us to extend the intervals for maintenance and servicing to once a year.”