"TenneT is well underway towards meeting its offshore expansion targets one year ahead of the plan"

TenneT has just installed its fifth offshore platform for the grid connection of offshore wind farms in the North Sea. The HelWin beta converter platform enables providing another 690 MW of offshore wind energy to the transmission grid, using direct current technology – equalling the capacity of a mid-sized conventional power plant.

"We have achieved another major milestone, gradually implementing the offshore expansion targets set by the German federal government," said Lex Hartman, management board member, TenneT. The German government intends an offshore wind capacity of 6.5 gigawatts by 2020. "TenneT is well underway towards meeting these offshore expansion targets one year ahead of the plan," Hartman em-phasizes, as – combined with the previously erected grid connections and the connections yet to be completed – the offshore wind energy transmission capacity in the German North Sea will amount to some 7.1 gigawatts by 2019. The four converter platforms erected by TenneT in the North Sea since autumn 2013 (also called transformer platforms, as they convert alternating current to direct current) alone enable delivering some 2.9 gigawatts of offshore wind energy onshore as of 2015. TenneT has already issued an invitation to tender for another offshore wind energy "socket" with a capacity of 0.9 gigawatts. This will be followed by a continuous addition with the award of grid connection systems with a capacity of 0.9 gigawatts each at intervals of around two years.

Siemens had completed the work for the recently installed HelWin beta offshore platform as the general contractor of TenneT. Jan Mrosik, CEO of the power transmission division, energy sector of Siemens AG, said: "The HelWin2 project is progressing well towards its final commissioning stage in 2015."

HelWin beta is a subsidiary platform of HelWin alpha. The shared use of the main platform HelWin al-pha's facilities, as for example the helideck, creates synergies that enable cost reductions. The HelWin beta platform is located only 20 m from the HelWin alpha platform, which was installed last year. A bridge will connect the two platforms. While serving to access the HelWin beta platform, the bridge will also be used to support cable connections between the two platforms.

Considerate technical challenges had to be overcome when installing the HelWin beta offshore platform 35 km north of Helgoland, the North Sea island, after which it was named. HelWin beta is connected to the onshore converter station in Büttel, using submarine and underground cables with a length of 130 km, the most of which have already been installed.

The foundation (jacket) for the converter platform was brought to its installation site in the North Sea in April. A crane vessel installed the jacket and mounted it to the seabed at the construction site. Subse-quently, the upper structure of the foundation (topside) was loaded on a transport barge and transported from Zwijndrecht, Netherlands, to the jacket site near Helgoland. Upon its arrival, the crane vessel lifted the topside on the jacket, where it was finally weld-mounted. The platform is 42 m wide, 98 m long and approximately 28 m high and weighs more than 10,000 tons.