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Offshore power cable extra €50 million due to data?

By: Tom Russell 26/06/2020 TenneT

Cables General Substations Windfarms

Dutch Transmission System Operator (TSO) TenneT has revealed the Borssele Alpha offshore wind grid connection project cost more than expected before installation works began. During subsea cable installation contractors found unstable soil conditions within a specific area cable route (the Northern slope of the Honte) which lead to increased costs.

Ahead of installation works, TenneT performed a route survey to investigate the physical conditions of the subsea cable route. This route survey was executed by an expert contractor who had extensive experience in performing similar surveys. The data of these surveys did not indicate the physical conditions of the Northern slope of the Honte. When executing the subsea cable installation these unstable soil conditions were discovered and made it necessary to apply a different working method.

The original contract was awarded to NKT Cables and VBMS (now part of Boskalis) with a value of €160 million. As a result of the discovery of unstable soil conditions, the work cost TenneT €210 million. Installation of the subsea cable was completed towards the end of last year.

The Borssele Alpha grid connection project will connect the Borssele 1&2 offshore wind farm to the onshore grid it. The projects included the installation of a 700 MW offshore substation, subsea cable and a new substation which has been built next to the existing 380 kV Borssele high voltage substation.

Borssele Alpha, TenneT's first alternating current (AC) offshore platform on the Dutch part of the North Sea, was and is now ready for use. Another seven of these 700 MW standardised platforms will be delivered by 2027 for connecting future offshore wind farms to the onshore grid. The next offshore connection system, Borssele Beta, will be completed by 2020. For the IJmuiden Ver wind area TenneT expects to use two 2 GW converter platforms in combination with 525 kV cable.

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Offshore power cable extra €50 million due to data?

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