Hollandse Kust Noord topside installed

4C Offshore | Tom Russell
By: 05/10/2022 TenneT

The topside for the offshore transformer station for the
Hollandse Kust Noord wind farm has been installed. The lift was completed using installation vessel Orion.

The installation of the topside took place during the night from Monday to Tuesday at 18.5 kilometres off the coast of Egmond aan Zee. It was be lifted onto a jacket foundation which was firmly anchored to the seabed in November last year. The topside is 47 metres long, 35 metres wide and 25 metres high. The topside and jacket be commissioned in the coming months.

"We had to wait until the installation vessel Orion was available and weather and tidal conditions offered us a favourable time window,"
said Guus Siteur, offshore platform project manager on behalf of TenneT.

According to Siteur, placing the topside went relatively quickly. "A large crane on the Orion lifted the 3,500-tonne steel structure off the floating pontoon. Both the jacket and the topside are attached to so-called cones. These can be compared to ice cream cones that fit together perfectly. This allows you to lower the topside in exactly the right place."

A jack-up barge (lifting vessel) has positioned itself near the platform to support committing works. Siteur added: "Once this has extended its legs and the ship is suspended above the waves like a platform, a walkway is suspended between the ship and the platform. Some 50 people will stay on the ship for the next few months. They will weld the topside to the jacket and take care of commissioning the installation."

Next month, TenneT will also test the fibre-optic connection, which has been laid together with the sea cables. It can then be commissioned to control the unmanned socket at sea. Siteur expalined: "With this, everything will soon be controlled from our operations centre in Arnhem. In addition to the transformers that bring the voltage level from 66 kilovolts to 220 kilovolts for efficient transmission, there are also 130 kilometres of cable in the topside to connect all systems."

The sea cables for 'north' are already ready in the seabed. Behind the dunes near Heemskerk/Wijk aan Zee, these will be connected to the cables that will soon feed the power into the high-voltage substation along the A9 in Beverwijk. In the coming weeks, the cables for (West Alpha) will also be laid at a safe depth in the seabed.

Each of TenneT's outlets at sea is deployed as a 'Maritime Information Service Point' for Rijkswaterstaat. This monitoring station includes radars, meteorological systems (for wind, precipitation, clouds and temperature) and ecological monitoring systems for birds and bats, for example. Siteur: "Biohuts are attached to the legs of the jacket to create breeding sites for fish. And structures are placed on the stone foundation where marine life can nest safely."

In total, the EQUANS/Smulders combination is building three topsides for TenneT. After 'north', 'west Alpha' will follow in 2023 and 'west Beta' in 2025. From the eponymous wind farms, the grid operator will make sustainably generated electricity available to households, businesses and industry via these sockets (together accounting for 2.1 gigawatts) in the coming years.