Dutch electricity transmission operator TenneT has awarded the contract of transformer construction for the Borssele offshore wind farm to HSM Offshore.

The contract concerns the offshore platform for the Borssele Alpha wind farm zone. HSM Offshore is also the intended partner for TenneT’s next offshore wind energy project, Borssele Beta.

The Borssele Alpha project, to be followed by the Borssele Beta project, are the first large-scale grid connections to be constructed under the National Energy Agreement for offshore wind farms in the Netherlands.


HSM Offshore will take on the engineering, construction, transport, installation, connection and testing of the offshore transformer station.

The Borssele Alpha platform will have a connection capacity of 700MW for offshore wind farms and is scheduled for completion in 2019. The Borssele Beta platform is expected to be completed by 2020.

TenneT has been officially designated as the offshore grid operator in the Netherlands, and will contribute to fulfilment of the National Energy Agreement by developing offshore grid connections with a total capacity of at least 3.5GW during the period until 2023.

These connections will be constructed in accordance with a standardized concept and will have a capacity of 700MW each.

The tender procedure for the subsea cables and platforms for the Hollandse Kust Zuid project will start in the second quarter of 2017.

Subsea cables

The total length of the route section from the onshore station at Borssele to the Borssele Alpha offshore transformer station (the “platform”) is approx. 61km. The offshore grid connection consists of two 220kV subsea cables with a capacity of 350MW each.

In a world first, the cables’ so-called “dynamic capacity” will be utilized. This means that a single cable can be temporarily subjected to a load of up to 380 MW.

The cables will be installed in the seabed of the Western Scheldt estuary and will run to the onshore high-voltage station at Borssele. The cables will be installed at a depth of 1m in the North Sea, and at a depth of 3m along the entire route in the Western Scheldt estuary, up to the point where they come onshore at Borssele.

In most locations the cables will be installed at even greater depths to cope with possible seabed movements. The contract for the supply and installation of the land and subsea cables for Borssele Alpha and optionally for Borssele Beta was awarded to a consortium made up of NKT cables GmbH & Co. KG and VBMS B.V. (Boskalis).