Last Monday, Allseas’ Pioneering Spirit successfully installed the topside of the Hollandse Kust (zuid) Beta transformer substation on the jacket foundation already in place. Together with the previously installed Alpha substation, they form part of TenneT’s offshore high-voltage connection for the Hollandse Kust Zuid offshore wind farm currently under construction.
At the invitation of TenneT, a boat tour took place yesterday to the two High Voltage Alternating Current transformer substations. The invited guests, including press from various media, departed on the hotel ship DP GaLyna of Chevalier Floatels yesterday morning from the harbour of Scheveningen to the wind farm Hollandse Kust Zuid, located around 23 kilometres off the coast.
HKZ Beta
The boat tour led first to the Beta station. While the installation of the topside took place in thick fog last Monday, visibility was good on Wednesday. At a small distance from the platform, the Pioneering Spirit that placed the 3,928-ton topside on the jacket was still visible. Contractor Petrofac was responsible for the fabrication of both the Alpha and Beta topsides. Both were built at the Drydocks World fabrication yard in Dubai. The Alpha topside was installed on Sunday 26 December 2021 on the jacket in the North Sea, about 20 kilometres off the coast of The Hague. The Beta topside left the Dubai fabrication yard last February and was transported by a Boskalis transport vessel to Alexiahaven on the Maasvlakte in just over a month, where it arrived last week to be loaded onto the Pioneering Spirit.
That the platform is now complete was still uncertain a few weeks ago. After the ship Julietta D, which was hit by the storm Corrie in January, hit the jacket, the contractor and the certifying body had to check whether the damage would not be too severe. Fortunately, the damage could be repaired and the installation could still take place. The coming months work will proceed on the preparation of the power supply and everything that comes with it.
HKZ Alpha
Shortly afterwards, we sailed past the Alpha platform. The JB 115 was still moored here so that Petrofac personnel could carry out the very last activities on this topside, which was installed in December 2021. Last week, the certifying body DNV GL had already issued the ‘Grid Readiness’ certification. This means that this offshore grid connection fully complies with the conditions as set out in the so-called “Development Framework for Offshore Wind Energy”. With this, the so-called ‘power point’ is ready to connect the future wind turbines of the offshore wind parks Hollandse Kust (zuid) I and II.
Hollandse Kust Zuid offshore wind farm (tendered in 4 lots) is to be completed in 2023. The 1.4 GW wind farm will feature 140 Siemens Gamesa 11 MW wind turbines. The project of Vattenfall and BASF is the first subsidy-free wind farm in the world. Installation of the foundations began in July 2021. Currently, 34 monopile foundations have been completed and the installation of the inter-array cables is to start. The first transport of wind turbine components will take place in May.
The electricity that will soon be collected from the wind turbines in the transformer stations will be converted here from 66 kV to 220 kV. The electricity will then be transported to the Maasvlakte substation via two export cables for each platform. At this substation, the voltage will be converted to 380 kV. Finally, the electricity is transported to the high-voltage grid via the Randstad 380 kV Zuidring substation.
Offshore connections
By the end of 2023, TenneT is scheduled to have 3,500 MW of offshore grid connections in place for offshore wind farms in the Dutch North Sea. The first 1,400 MW were realised with the completion of Borssele Alpha and Beta in 2019 and 2020. Now it is the turn of Hollandse Kust (zuid) Alpha and Beta this year, followed by Hollandse Kust (noord) in 2023. TenneT is building five identical 700 MW transformer platforms for these wind farms. These platforms will be located close to the wind farms and all five will use the same type of 220 kV cable connection to the coast. This standardisation will enable TenneT to carry out these projects more efficiently, more quickly and more economically.
