Ørsted and Vattenfall link up offshore wind farms in the North Sea

A new eight-kilometre cable between Horns Rev 2 and Horns Rev 3 allows the two offshore wind farms to supply each other with electricity if the export connection to land is disconnected. The cable was used for the first time recently when the Danish system operator, Energinet, disconnected the export cable to Horns Rev 2 for four-days of scheduled maintenance work.

The owners of the two offshore wind farms, Ørsted and Vattenfall, invested in the 33 kV cable that creates additional security for the two energy companies’ billion-kroner investments in the North Sea. If there is a problem with the export connection to land, this is not only critical for the supply of electricity to customers on the mainland; it is also critical for the wind turbines.

Horns Rev 3 wind farm

“Offshore wind turbines must always be supplied with electricity; otherwise there is a risk of significant damage from for instance  humidity. The cable also enables a quick and easy start-up of the offshore wind farm once the export connection is back in service. In addition, we save a lot of diesel fuel and operating hours for the emergency generators for both the wind turbines and the service boats”, points out Niels Møller Jensen, Interface Manager at Horns Rev 3.

The cable, which was completed in April, is an optimal solution both in terms of the environment and with regard to investments and operating costs. It was used for the first time recently when Energinet had to disconnect the export cable from Horns Rev 2 for four days for maintenance works. During this time, the wind farm was supplied with electricity from Horns Rev 3.

“We are really happy that we could supply our 91 wind turbines with back-up electricity from Horns Rev 3 during Energinet’s planned inspection of the export cable’s high voltage switch. Thanks to the new cable, we were able to resume generation of green power much faster”, says Allan Due Overbeck, Head of Operations Horns Rev 2.

The wind turbines at Horns Rev 2 normally get emergency power from a central generator on an offshore platform. At Horns Rev 3, each turbine has a small emergency generator.

This is the first time the two offshore wind farms, which have different owners, have backed each other up in this way. Horns Rev 2 has been in operation since 2009, while Horns Rev 3 first began supplying power to the electricity grid in December and will be operating at full capacity by the end of the summer. By Esben Baltzer Nielsen