IN DEPTH: HelWinbèta on the move

The office-block-size yellow box making its way slowly down the River Oude Maas in the Netherlands looks nothing like an electrical socket.

Yet the 10,200-tonne HelWinbèta topsides is the fourth of ten giant converter stations being delivered one by one for transmission system operator (TSO) TenneT’s pioneering plan of plugging in more than seven million homes to wind projects now being developed in the German North Sea.

Its size squares with the TSO’s wider ambition. HelWinbèta — which is 98 metres long, 42 metres wide and 28 metres tall — will be the heart of the 690MW high-voltage direct-current (HVDC) HelWin2 transmission hub. Together with the already installed 576MW Helwin1 station, it will wire in a cluster of wind farms near the island of Amrum, converting alternating current (AC) into DC and sending it 130km to an onshore grid connection.

Built by the Dutch Heerema Fabrication Group (HFG) for contractor Siemens under an all-in EPCI (engineering, procurement, contacting and installation) deal that included Italian cable-maker Prysmian for the spur and export lines, HelWinbèta bristles with the latest HVDC equipment.

The seven-deck platform has been engineered around the German giant’s HVDC Plus technology — a modular voltage-sourced converter (VSC) system that can carry up to 1GW and juice up from cold starts — as well as two 670MVA power transformers, high-specification air- and gas-insulated high-voltage switchgear, all with environmentally friendly neutral electromagnetic fields.

“This EPCI project stands out because of its complexity and size,” says HFG chief executive Koos-Jan van Brouwershaven. “We managed and built both the jacket and topside in a relatively short period of 20 months, a significant performance and quite unique for wind energy projects.”

Though the construction took under two years at HFG’s Zwijndrecht yard, the total €500m ($680m) HelWin2 project has been a watershed for TenneT after its initial overoptimism in getting industrial-scale offshore power hubs into place and switched on. HelWinbèta took around four years to get from first spark of conception to float-out — on-time to a rejigged schedule, but much longer than the 33-month project timeline set out by the TSO for earlier converter stations HelWin1, BorWin2 and SylWin1.

“To be sure, the first three [converter stations] were delayed. But for HelWin2 things look stable in the delivery to [TenneT’s] plan [to have HelWin2 online by 2015],” says Siemens Transmission Solutions chief executive Tim Dawidowsky.

“There are enough lessons learned from these four projects for processes to be working smoothly now. On the manufacturing side, there are more reasonable views of what it takes to build a topside — 33 months was always going to be unrealistic.

“Things are now being cleared, ticked off, approved before we start manufacturing — changes during execution were a major concern before now.”

The experience has led TenneT to rethink its converter station projects around a 60-month timeline, even affording an extra year’s buffer for slippage.

Once HelWinbèta is commissioned next year, the first wind farm to be connected will be E.ON’s 288MW Amrumbank West, with the neighbouring Meerwind Süd/Ost and Nordsee Ost projects cued up to follow.

Electrical current will be generated at the turbine at 33kV, then stepped up to 155kV at the offshore substation, before being sent to the HVDC converter station, where it will be converted into 320kV for transmission to the onshore substation at Büttel, where it will be switched back to AC and enter the grid at 400kV.

As part of the original package of contracts for HelWin2, Prysmian is supplying bespoke HVDC cable for 85km of subsea offshore transmission line, plus a 45km stretch to reach the onshore substation.

“HelWin2 is the next piece in the puzzle of our plans to construct 7.1GW of offshore transmission capacity,” states TenneT executive board member Wilfred Breur.

“This [capacity] is more than the German government’s goal of having 6.5GW installed by 2020, but it is a bit like a highway in that you would need to build wider roads, a bit more capacity, to prevent traffic congestion. We have other projects [including DolWin3 and BorWin4] consented and ready for tender.”

After the project miscues of the first three German hubs, this past April proved a breath of fresh air for the TSO, with the 4,500-tonne jacket for HelWinbèta piled in, the topsides for BorWin2, to the west of it, being installed, and a contract for the gigantic 900MW BorWin3 link awarded to Siemens.

“I feel really positive about [the lessons learned by industry from these projects] because the projects that are coming can be tackled with less difficulty,” says Dawidowsky. “Although they are complex, they are more manageable in a way that previously they couldn’t be — both on the technical and project execution side.

“Moving forward with the new set-up that TenneT has laid out with respect to delivery times, expectations are more realistic.

“This is a good sign for the industry as a whole, because there were question marks in the very beginning about the [project] concept in general. Now the opposite is being proved. Everything is going in the right direction and to sensible timelines.”