Every structure has a ‘crucial detail’. At the Gemini wind farm, that might be the offshore cables that connect the farm to the land. A total of 208(!) km of cable, with a diameter of about 30 cm. What exactly goes into the cable? Richard Koning explains.

The Gemini business card that he has carried with him since January 2014 says ‘Package Manager Submarine Cable Production’. He knows everything about the cables that connect the wind farm to Eemshaven. The cables have been applied before and therefore constitute ‘tried and tested’ technology. ‘But what makes the operation unique is its length. Three sections, 95, 10 en 103 km long in a ring; that has never been done before. Not with this sort of cable, carrying 220,000 volts.’ Richard takes the cross-section of the cable and talks us through the technical specifications. ‘The energy generated by the turbines runs through three conductors, which are surrounded by a plastic layer to insulate the 220,000 Volts from the earth. The lead coating around that keeps this insulation free from the seawater and also performs the function similar to the protective conductor in an ordinary electrical wire. As a comparison, if you were to hang a conductor in the air with no insulation at a similar voltage, you would have to keep a distance of at least three meters. That’s how high the voltage is.’ An extra synthetic layer around the lead coating gives it extra strength and ensures that it does not come into direct contact with the environment.

Steel armouring

Rubber filling is used in order to create a fine round whole of the three cores that together make up a triangular cable. ‘This filling also keeps the fibre optic cable, which connects the stations and the turbines, in place. All data on the functioning of the wind farm is transmitted along this cable. This cable, too, is encased in order to protect it from external influences.’ The outside of the cable is protected with steel armouring to shield it from fishing nets or pieces of rock that might fall onto the cable. ‘This layer of 8 mm steel wire wound around the cable gives it real mechanical strength. The final outer coating consists of a mix of synthetic strings held together with bitumen. This also carries the colour codes that show what sort of cable this is and who it belongs to.’ Because the cable is not laid all at once, connectors are fitted at regular intervals, similar to the thermoplastic connectors used in domestic wiring. ‘They are just a bit bigger than the ones used at home’, Richard Koning explains. ‘In total, including the casing and end-pieces, they are about 20 metres long: they look like mini-submarines.’

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