Effective works Phase 2 - 3
2012 : week 38
The concession of C-Power in the North Sea for the erection of a windfarm is divided into two area's, area A and area B. In area A 30 wind turbines and an offshore transformer station will be installed. In area B 24 wind turbines will be installed. The execution of the project is devided in three phases. Phase I, terminated in 2008, was a test phase with the installation of 6 wind turbines in area A on gravity base foundations. Phase II, terminated end of August 2012, consisted in the installation of 24 wind turbines in area B, 6 wind turbines in area A and an offshore transformer station also in area A. Phase III will be executed next year, 2013, and consists of the installation of the remaining 18 wind turbines in area A. This phase is planned to start in March 2013 and to be completed in September 2013.
All the wind turbines are erected offshore on jacket foundations. A jacket foundation is a steelstructure of tubulars designed to support the windturbines. The height of a jacket varies between 40 and 50 m. The construction of the 48 jacket foundations of the project started in Januari 2011. 9 months later the first 24 jackets for area B were assembled. The construction of the 24 jackets for area A followed immediately hereafter in September 2012. 7 months later, April the 1st 2012, they were all assembled. So in a total of 16 months all 48 jacket foundations were build.
The pile driving works started in area B of the windfarm on Wednesday 6th of April 2011. Steel piles of 40 to 50 m are driven into the seabed by a hammer installation mounted on the jack up platform Buzzard. These so called "pin-piles" are the anchors to seal the jacket foundations into the seabed. The length of the piles depends on the soil conditions. To assure an installation of the piles on the correct locations a template is lowered onto the seabed. On Sunday August the 21st 2011 all pile driving works for the project were complete which means that 196 piles were driven into the seabed in about 4,5 months.
The jacket foundation installation for the offshore transformer station, (OTS), was executed on the 15th of August 2011.
The Heavy Lift Vessel "Rambiz" installed the first jacket foundation for the windturbines in area B on Sunday 12/06/2011 and on Tuesday 14/06/2011 this foundation was grouted to the pin-piles. On 28/09/2011, so after a period of 3,5 months, all the 24 foundations of area B were successfully installed and grouted. The Rambiz was again mobilised to start on 2/03/2012 the foundations installation in area A and on Tuesday 29/05/2012 the last jacket was installed and grouted. All 24 jackets of area A were installed in 3 months and the completion date was 2 months ahead of the original master schedule.
The 33 kV infield cables of area B, making the future electrical connection between the wind turbines, were picked up in Karlskrona, Sweden, on the 23th of July 2011 and were transported to Zeebruge by the cable lay vessel CS Sovereign. The infield cable laying works for area B started on 12/08/11 and were completed on 3/11/2011. A cable burial vessel, called the Innovator, jetted down these cables into the seabed. Two teams of special trained people did the final hang off of the cables in the so called mid-sections of the WTG foundations. The production of the infield cables for area A was also done in Karlskrona. The same cable lay vessel as for area B, the Sovereign, was again mobilised and picked up the infield cables in Karlskrona on 12/06/2012. The ship arrived on site on 24/06/2012 and started with the infield cable laying in area A on 28/06/2012 after the wet trials. Today all the infield cables of area A are laid down and connected to the mid sections of the WTG's. The burial of these cables started on 9/08/2012 and all the cable strings between the offshore transformer station and the wind turbines got a first burial pass. The surveys of the burial depths are complete and where necessary some remedial burial works will be executed. The vessel Innovator has been mobilized for that job.
The produced electricity by the wind farm has to be brought on land by two so called export cables. The first export cable, cable A was laid during phase I. The second 150 kV export cable, cable B, has to be laid during phase II. The cable was manufactured in Karlskrona, Sweden. The factory acceptance tests were carried out on 13/03/2012. The cable lay vessel "Stemat Spirit" loaded the cable in Karlskrona between 22 and 29/03/2012, sailed to and arrived in the port of Ostend on 4/04/2012. The vessel beached at the cable landing area and the export cable B was pulled on land through a HDD pipe on 11/04/2012. On 22/04/2012 the complete 38,7 km of export cable was laid down on the sea bed between the coast and the Offshore Transformer Station. The vessel Pearl River backfilled the cable trench. The trajectory of the export cable in the shallow waters was jetted down into the seabed. The 150 kV export cable was then pulled in into the OTS. The connections of the cable conductors and fibre optics were terminated and passed a succesful 24 H test on 30/05/2012. This means that the electrical connection between the offshore windfarm and the onshore substation of Elia was then energized, which was a very important milestone for C-Power.
A dredging vessel, the "Breughel", prepared the trench where the 150 kV export cable B is crossing the shipping lane "Vaargeul 1" and in a part of the trajectory where a seabed was found of stiff clay.
The trajectory of both export cables crosses two international communication cables and an international gas pipe. These crossings need special attention and protection. They were protected by asphalt mattresses before the export cable laying and will now been protected by rock dumping after the export cable laying. For the moment the rocks for this rock protection are being delivered on the Halve Maan site of C-Power at Ostend. A rock dumping vessel, the Pompëi has been mobilized for this job.
The Offshore Transformer Station sailed out from the fabrication yard in Schiedam to the Thorntonbank site on the 15th of March 2012 and was installed on the OTS foundation on 16/03/2012.
The productions of the wind turbines components were carried out at different locations: the towers by AMBAU-Cuxhaven Germany, the blades by LM Glasfiber Holding Denmark, the generators by VEM Germany and the gearboxes by 2 constructors, WINERGY-Vörde Germany and HANSEN-Belgium. An onshore offloading, assembling and loading site for the wind turbine components of REpower in the harbour of Ostend was rented and prepared to receive these components. The first set of blades arrived on the onshore site of Ostend on 2/03/2012 and the first batch with 3 towers, hubs and nacelles on 7/03/2012. Every week new turbine components arrived in Ostend, either by sea or by land. Since 22/06/2012 the components of the last 3 wind turbines of phase II arrived in Ostend. So all the deliveries for the phase II of the project were on site on time. The productions in the factories of the components of phase III WTG's started in June 2012.
A jack up transport and installation platform, the Neptune, sailed out on 18/03/2012 to the Thorntonbank for the first WTG erection. Another jack up platform, the Vagant, assisted the turbine installation teams with the mechanical completion of the wind turbines. On 21/03/2012 the first wind turbine was installed. On Friday the 27/07/2012 the 30 wind turbines that has to be erected this year were installed. So it took about 4 months to install 30 wind turbines. The transport and installation jack up platforms Neptune and Vagant were then demobilised from the project. They are scheduled to come back in March next year for the installation of the last 18 WTG's of C-Power's project. Special teams executed the terminations of the infield cables into the wind turbines. As the export cable B was energized the commissioning of the WTG's could start. For the commissioning of the WTG, the 33 kV infield cables between the offshore transformer station and each wind turbine had also to be energised. Today all of the 5 strings of infield cables of phase II are completely energised. It takes about a week to commission 1 wind turbine. At the start of the commissioning of the first wind turbine of phase II the first KW's were injected into the grid on 2/06/2012. Today 28 WTG's out of 30 of phase II are commissioned and are producing electricity. Reliability tests are now undertaken.
The horizontal directional drillings under the dunes for the onshore landing of the second export cable coming from the windfarm offshore transformer station was successfully completed on 5/3/2012 and the cable laying onshore between this export cable landing and the Elia sub-station was completed at the same time. The connections of the cables into the Elia sub-station were also completed. Electrical commissioning tests on the complete onshore cable connections were successful. The new export sea cable and the new land cables were jointed together.
Another important milestone in the C-Power project has been achieved: the 6 wind turbines of the first phase were connected to a temporary sub-station onshore via the first export cable A between the turbine D1 and the sub-station. Today the temporary sub-station has been replaced by the offshore transformer station. So the wind turbines of phase I had first to be disconnected from the export cable A of phase I and had to be energized via the new export cable B and the offshore transformer station. After that operation the first export cable A from phase I has been disconnected from the wind turbine D1 of phase I, has been cut and sealed and re-routed to the OTS. The cable has been picked up from the seabed and pulled in into the OTS. Special teams de-armoured the cable phases and connected them to the OTS. On Tuesday 14/08/2012 the export cable A was re-energised. The transformer in the OTS linked to that export cable has been energised on 13/08/2012. Thanks to that operation the windfarm is now connected to the onshore sub-station of Elia with two 150 kV sea cables.