With the completion of DolWin alpha, another converter platform for the German North Sea is now ready … more or less. The final installation at sea is still subject to delays.
There it stands, in Schiedam near Rotterdam, waiting to be transported to the open sea off the German coast and to be installed in the waiting jacket construction. At least, that was the situation when this article went to print – its departure could take place any day now.
The delay is due to the crane vessel Thialf. The finished transformer platform DolWin alpha has already been waiting for the vessel for several months. Thialf is the only floating crane in the world that can install a construction of this size, but the ship is still busy elsewhere. And DolWin alpha is on the limit, even for Thialf’s capacities: the helicopter deck, the living quarters and even one of the two transformers will only be installed after the platform is sitting safely on its jacket. Otherwise the platform would be too heavy and even Thialf would be unable to lift it in such depths. And getting it from the Heerema dockyard in Zwijndrecht to Schiedam would also have been impossible; as it was, it passed under some of the bridges over the Oude Maas by just a few millimetres. With the helicopter deck on top it would have been too high.
Learning from experience
The connection capacity of the DolWin alpha platform is 800 MW. It will be the central HVDC transformer station for the DolWin offshore cluster, and the three wind farms Borkum West 2, MEG Offshore 1 and parts of Borkum Riffgrund 1 will be connected to it. But that is not the end of the rope. “900 MW is the optimal size in terms of the cost efficiency of the platforms,” says Mel Kroon, CEO of TenneT. That would correspond to the maximum capacity of the cables. And that is why platforms are now being built that are larger than current needs, Kroon explains. This is what TenneT and others have learnt from their early projects.
The same goes for Heerema. The Dutch dockyard had already built the transformer station BorWin alpha, which, like DolWin alpha was also a contract for ABB. “We are learning”, assures Heerema’s Chief Operating Officer Wim Matthijssen: “Compared to BorWin, we have come a long way.” The wind power industry presented some challenges in the form of requirements that Matthijssen was not familiar with from the oil and gas industry, such as environmental impact measures like noise reduction.
Whether you listen to people from TenneT, Heerema or from the general contractor ABB, they all emphasize the progress that has already been made. Between the lines, however, is the message that there is still a lot of room for improvement.
Standing at the foot of the converter platform, one is overwhelmed by its sheer size. But it is when walking through the halls of DolWin alpha that you fully appreciate the dimensions of the construction. You do end up wondering, though, why the thing needs to be so huge. After all, much of the interior is just empty space. Hanspeter Fässler from ABB provides the answer: “Because air is the only insulator, there needs to be a lot of open space to prevent electric arcs and similar phenomena.”
International project
DolWin alpha is a truly international construction. The HVDC light technology used is based on power semiconductors developed and manufactured in ABB’s facilities in Switzerland. HVDC valves and control systems are engineered and assembled in Sweden. And the transformers and the HVAC equipment are manufactured in ABB’s facilities in Germany. Then of course there is the construction work in the Netherlands. Heerema built the jacket construction for the platform in Vlissingen and the topside in Zwijndrecht. Engineering was provided by Iv-Oil & Gas. The Dutch company Heinen & Hopman was responsible for the design and engineering of the heating, ventilation, air conditioning and chilled water systems, as well as the supply of all pumps, appendages, control equipment and piping on this giant offshore converter platform.
At the moment there is only one operational HVDC converter station in the world: BorWin alpha. DolWin alpha will be the second once it is installed – or sometime thereafter. The final steps before it becomes operational could still take time. In May, DolWin alpha left the Heerema dockyards in Zwijndrecht and was loaded onto a seagoing barge. It then sailed away to Schiedam for further completion. At the time, installation at sea was planned for the summer. The next steps would then be laying the cables to the onshore converter station and testing the grid connections. Then Borkum West 2 would be the first wind farm to be connected. But first, DolWin alpha must wait for Thialf.
Katharina Garus
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