The start of production at LS Cable in Donghae (South Korea) yesterday marks the beginning of a new technological chapter for TenneT’s offshore grid connection systems. The new cables with a voltage of 525 kilovolts (kV) raise the transmission capacity for offshore wind energy to a new voltage level. They make it possible to transmit two gigawatts (GW) of direct current over long distances with low losses. Up to now, 320 kV cables have been used for offshore grid connections, for example, in TenneT’s 900 MW projects.

The start of cable production is part of the framework agreement that TenneT concluded with the consortium consisting of the Jan De Nul Group, LS Cable & Systems and Denys in May 2023. The contract covers the production and installation of four 525 kV DC cable systems for the TenneT grid connection projects in the North Sea. The first DC cables produced by the South Korean cable manufacturer LS Cable are intended for the BalWin4 and LanWin1 grid connection projects.
In addition to a positive and negative pole, an additional cable – a so-called metallic return conductor – will be laid for both grid connections in future, which will ensure that electricity can continue to flow in the event of maintenance or repair work. The three cables will be supplemented by an additional communication cable.

A total of 1,650 kilometres of cable will be produced for the BalWin4 and LanWin1 projects (route length per project: 275 kilometres, of which 165 kilometres are submarine cables and 110 kilometres are land cables). The inner conductor is made of copper, which makes the cables real heavy-weights. The submarine cables alone weigh around 76 kilograms per metre. The total weight for the submarine cable (plus/minus pole) is, therefore, around 25,000 tonnes per project – a logistical challenge.

The cable production will be completed in 2028, and cable laying at sea is expected to begin in the second half of 2026. The Jan De Nul Group will use the extra-large cable-laying vessel ‘Fleeming Jenkin’, which was specially designed and ordered for transporting and laying the 525 kV DC cables on the seabed.

The Construction of the land cable is also scheduled to start in the second half of 2026 by the construction company Denys, with work being carried out, as usual, using the open trench method with a cable trench and the closed trench method using horizontal drilling. These will be used to cross bodies of water and existing infrastructure such as railway lines, dykes, roads and the like.

BalWin4 is scheduled to go into operation in 2029, and LanWin1 in 2030.

Image source: Courtesy of TenneT

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