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Onshore cables connected for Windpark Fryslân

4C Offshore | Tom Russell
By: Tom Russell 22/03/2021 Windpark Fryslân

Onshore cabling works for
Windpark Fryslân have been completed and the cables are ready for use. The connection to the Oudehaske high-voltage substation near Heerenveen features a 55 kilometre-long underground 110 kV cable running along the A7 motorway.

The cables of the wind farm and high-voltage grid operator TenneT have been welded together at Bolsward and successfully tested. The weld (or the so-called 'terminal block') between the high voltage cables is a temporary application. TenneT is currently preparing a new high-voltage substation to the west of the De Marne business park near Bolsward. When it comes online, the connection of existing and new cables will create an extra 'ring' in the West Frisian high-voltage grid from 2023, which will increase the reliability of the electricity grid in addition to capacity.

At the beginning of 2019, contractor Visser & Smit Hanab started the construction of the cable connection for TenneT and the Zuiderzeewind contractor consortium. At the request of the Windpark, approximately 23 kilometers from Breezanddijk were constructed across the Afsluitdijk to Bolsward. From Bolsward (for TenneT) 32 kilometres to the Oudehaske high-voltage substation near Heerenveen. As a whole, this 55-kilometre connection is the longest underground cable connection constructed in the Netherlands.

The cable connection is parallel to the A7 motorway. 60% of it was constructed in open excavation, and the rest was drilled under waterways and motorways. Because the route usually runs along a narrow roadside strip, the cables are partly above each other. In order to properly dissipate the heat released by the high-voltage cables and to prevent drying out and overheating, all cables are laid in a layer of loamy sand. A total of 196 kilometres of power cables were buried for TenneT and another 150 kilometres for
Windpark Fryslân.

Tim Christiaans, TenneT Project Manager, said: "The construction was complex, partly because the connection is on the verge of the motorway with little space and a lot of traffic. The project as a whole has been successful and safe. No incidents and accidents. That's the most important thing."

Bart Ummels, Engineering Manager Windpark Fryslân: "We have been working closely with TenneT since 2016 to realize this challenging route on time. This connection is essential for the wind farm: no green electricity without a grid connection! I am proud of this milestone and I would like to thank TenneT and contractors ZuiderZeeWind, Visser & Smit Hanab and Prysmian for their good work and safe execution."

Last year, TenneT and Windpark Fryslân sown various strips of soil above the cable connection with indigenous flower species in the summer and autumn: a 'flowerline' on the 'powerline'. It is an initiative of Honey Highway that creates living space for insects, bees and butterflies in several places in the Netherlands along infrastructure. The realisation of this along the A7 was realigned in collaboration with Windpark Fryslân, construction consortium Zuiderzeewind (consisting of Siemens Gamesa and Van Oord), Visser & Smit Hanab, TenneT and Rijkswaterstaat Noord-Nederland.

The 382.7 MW
Windpark Fryslân is being built in the IJsselmeer near Breezanddijk and will be the largest inland water wind farm worldwide. When full operations are achieved this year, the wind farm will generate around 1.5 terawatt hours (1,500,000 megawatt hours) of power annually, enough green electricity to power approximately 500,000 households.

In addition to the 89 wind turbines at Breezanddijk, Windpark Fryslân consists of a newly constructed nature island at Kornwerderzand and a special transformer station on Breezanddijk, which will be open to the public from next summer.


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