monitoring & evaluation of blyth offshore wind farm...
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MONITORING & EVALUATION OF BLYTH OFFSHORE WIND FARM
INSTALLATION & COMMISSIONING
ETSU W/35/00563/REP/1
DTI/Pub URN 01/686
ContractorAMEC Border Wind
Prepared byL Pepper
The work described in this report was carried out under contractas part of the New and Renewable Energy Programme, managedby ETSU on behalf of the Department of Trade and Industry.The views and judgements expressed in this report are those of thecontractor and do not necessarily reflect those of ETSU or theDepartment of Trade and Industry.
First published 2001 Crown copyright 2001
This is the first of seven reports to be published on specific areas covered bythe monitoring and evaluation of the Blyth offshore wind farm project.The purpose of the reports is to evaluate and review the practical aspects ofinstallation, access, operation and maintenance of the first UK offshore windfarm.
The other reports are as follows:
NAVAID Requirements for Offshore Wind FarmsW/35/00563/REP/2
Review of Capital ExpenditureW/35/00563/REP/3
Health and Safety GuidelinesW/35/00563/REP/4
Review of Operational CostsW/35/00563/REP/5
Review of Operational AspectsW/35/00563/REP/6
Review of Wind Turbine Technical PerformanceW/35/00563/REP/7
The overall planned duration for this monitoring and evaluation project is 24months.
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EXECUTIVE SUMMARY
1) THE AIM AND OBJECTIVES OF THE WORK
The principle aim of this report is to appraise the practical aspects ofinstallation and commissioning of the offshore wind farm. The constructionand installation activities of the project were monitored and reviewed by theproject team to enable recommendations for future larger projects to be made.
This report particularly looks at how the project progressed against theconstruction and installation schedule with regard to weather conditions andoperational procedures. The document not only describes the methods ofinstallation, assembly and cable laying, but also reviews the effectiveness ofthose methods including any difficulties that were encountered and thesolutions that were found.
2) OVERVIEW OF THE PROJECT
The wind farm off the coast of Blyth, Northumberland, is the first offshorewind farm to be built in the United Kingdom. Two 2 MW wind turbines havebeen installed at a distance of approximately 1km from the coast, in a waterdepth, at low tide, of about 6m with a tidal range of approximately 5m. Thecompleted project is the first in Europe to be exposed to the full force of theNorth Sea weather as well as a significant tidal range. The site is also subjectto breaking waves.
The site location is on a submerged rocky outcrop. A chart showing thelocation of the turbines and the cable route is in Appendix A. Each windturbine has been erected onto a steel pile (monopile) that was drilled andgrouted into the rock. The 3.8m diameter holes for the pile were drilled froma jack-up barge (the Wijslift), and the pile lifted off the supply barge by thecrane on the jack-up barge and allowed to sink into the drilled socket. Themonopile was then grouted into position and allowed to cure. When it hadbeen confirmed that the monopile was secure in the hole, the sequence oferection was tower, nacelle and finally the rotor with the three blades attached.
The site has the benefit of all the consents required for the installation of theturbines. An Environmental Assessment was produced and detailed siteinvestigation studies were carried out and evaluated in order to complete thedetailed design of the structure.
The Blyth Offshore Wind Farm has been developed by Blyth Offshore WindLimited, a joint venture company between Powergen Renewables, Shell, Nuonand AMEC Border Wind. The diversity of experience and skills within theseorganisations has been brought together to pioneer the first project in whatpromises to be a new and exciting industry for the UK.
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3) SUMMARY OF WORK CARRIED OUT
The basic gantt chart below shows the planned activities against the actualactivities, highlighting the delay to the start of installation and the effect that ithad on the tasks that were linked to it. The delay in starting installation wasprimarily due to bad weather, particularly high winds and stormy seas.Limiting factors were set and during installation lifting operations could onlytake place on site when the wind speed was 8m/s or less and the swell nogreater than 0.5m. If the weather conditions were not within the limits thenthe installation operations had to be postponed until improved conditions wereforecast.
Gantt Chart Showing Actual v Planned Activities
ID Task Name
1 Joint Venture Agreement
2 Main Contracts in Place
3 Turbines Delivered
4 Monopiles Delivered
5 Modifications to Wijslift
6 Turbine Installation
7 Cable Laying
8 G59 Test
9 Commissioning
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The Gantt chart summarises the work that was carried out into 9 main areas,the full details of which are given in the main body of this report. The chartshows the difference between the planned and actual timings of the installationand commissioning activities.
Some changes were made to the planned procedures: namely the blade liftingprocedure, and the route of the cable connecting the wind farm to shore. Thebiggest issue of all was the weather. This was always going to be an issue andobviously could not be relied upon.
Installation had been planned for the summer months in the hope of reducingthe possibility of bad weather unfortunately the weather did not meetexpectations. Many of the installation procedures could only be carried out in
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very low swell and low winds. There were no solutions to the weatherproblems other than to constantly monitor weather forecasts and be ready togo whenever conditions were suitable.
4) CONCLUSION
In conclusion the installation and commissioning of the Blyth Offshore windfarm has highlighted many implications that should be taken intoconsideration for future offshore wind farms. The four major ones arediscussed briefly below and in more detail in Section 6 of the report. Ingeneral terms future project teams should review their methods and operationsthroughout the installation and take into account and act on any lessonslearned.
Installing a larger offshore wind farm would not require any more personnelthan were involved on the Blyth Offshore project, if anything fewer peoplemay be needed if the pile foundations are driven in, instead of drilling andgrouting them in place. Fewer people are involved in pile driving operationsand it also takes less time to drive a pile foundation in than to drill a hole,install the pile and grout it in place. However, the other aspect to consider is iftwo lots of equipment (2 x crane barge and flat barge) were used thenobviously twice as many people would be needed and it would in theory takehalf the time.
4.1 Equipment
For future larger projects further offshore it would be preferable to have acrane barge that can jack up above the swell to lift and install the pilefoundations and the turbine components, and a flat barge that could also bejacked up during lifting operations, to transport the components to site. Theadvantage being that if the barges were jacked up way above high water thelifting operations would not be subjected to any problems caused by swell.
Accommodation is another issue to consider when planning equipment.Obviously larger sites are going to be further offshore and quite probablysome distance from ports, which means that daily transfer of personnel willnot be an option. The only solution to this would be to have the personnel stayon the barges on site during the installation.
The final point to mention on equipment is self-propelled barges. The onesused during the installation of the Blyth Offshore wind farm were not self-propelled and had to be towed to site by tugs. While this did not cause anyproblems in the relatively short journey that had to be made from the RiverTyne to site, it would have implications for larger offshore sites. Towingbarges to a site further offshore would have an impact on the time that itwould take to travel to site from port. Self-propelled barges would take lesstime to move to and from site and then once on site would be able tomanoeuvre into position without the assistance of tugs.
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The installations of offshore wind turbines are so dependent on the sea stateand can be held up with severe delays even in supposedly “good” weathermonths. Each delay in the installation programme is lost generating time andan increase to the cost of the project. If commissioning a specialist vesselconsiderably reduces these delays then the case is obvious.
4.2 Weather
Installation would be planned for “good” weather months, however not a greatdeal can be done to prevent delays due to weather. A flexible working plancould be implemented to enable parts of the project to be carried outsimultaneously. If there was a delay on one part of the project, work couldstill be progressing on another thus avoiding delay to the overall plan.
4.3 Site
Full information on the seabed conditions of a prospective offshore wind farmsite will be needed initially for the design of the foundations. For instance ifthe intention is to drive pile foundations rather than drilling into rock then it isparticularly important to know the seabed conditions as a certain depth ofsediment will be needed for pile driving. (Piles cannot be driven into veryhard rock).
The seabed conditions are also very important to the barge operators of theinstallation equipment that would be used. When the barges jack-up they puttheir legs down on to the seabed, and the operators need to know theconditions that they will be working with. Primarily they need to establish ifthe barge can operate at that site and secondly to plan their operations andprocedures.
4.4 Electrical Protection
Although this was not an issue with the Blyth Offshore wind farm there willbe implications for larger offshore wind farms. The Electricity AssociationEngineering Recommendation for G.59 – “Recommendations for theConnection of Embedded Generating Plant to the Regional ElectricityCompanies’ Distribution Systems” is only valid for generation up to 5MW.For much larger wind farms the G.59 protection would not be used, a moresophisticated protection system would need to be in place. This would bedetermined from investigations and discussions with the Distribution NetworkOperators and also the National Grid Company.
This offshore wind farm was a first and hopefully this report goes some way tohighlighting the issues and how they were dealt with.
CONTENTS
1 INTRODUCTION ..................................................................................1
1.1 BACKGROUND.......................................................................................11.2 AIMS & OBJECTIVES OF THIS REPORT...................................................31.3 EQUIPMENT USED .................................................................................41.4 SEA CONDITIONS ..................................................................................5
2 INSTALLATION....................................................................................7
2.1 PLANNING AND SCHEDULING................................................................72.2 CASING INSTALLATION & SOCKET DRILLING .......................................72.3 SPOIL DISPOSAL....................................................................................82.4 MONOPILE ..........................................................................................102.5 TOWER INSTALLATION........................................................................132.6 INSTALLATION OF THE ROTOR ............................................................172.7 INSTALLATION OF THE HIGH VOLTAGE TURBINE CABLE ....................20
3 CABLE LAYING .................................................................................22
3.1 OPTICAL FIBRE PACKAGE ...................................................................223.2 PLANNING AND SCHEDULING..............................................................223.3 BEACH PREPARATORY WORK.............................................................233.4 VESSEL ...............................................................................................243.5 NAVIGATIONAL AIDS..........................................................................243.6 CABLE LANDING.................................................................................243.7 DIVING OPERATIONS...........................................................................253.8 CABLE LAY OPERATIONS BETWEEN THE NORTHERN & SOUTHERN
TURBINES.....................................................................................................253.9 CABLE LAY OPERATIONS ACROSS THE RIVER BLYTH ........................263.10 WEATHER CONTINGENCIES............................................................273.11 DAILY REPORTING .........................................................................28
4 COMMISSIONING .............................................................................30
5 ISSUES ..................................................................................................32
5.1 BLADE LIFTING PROCEDURE...............................................................325.2 CABLE ROUTE ACROSS THE RIVER .....................................................325.3 WEATHER ...........................................................................................335.4 INSTALLATION DIFFERENCES..............................................................34
6 IMPLICATIONS FOR FUTURE PROJECTS .................................36
6.1 EQUIPMENT.........................................................................................366.2 WEATHER ...........................................................................................376.3 SITE ....................................................................................................376.4 ELECTRICAL PROTECTION...................................................................37
APPENDIX A – TURBINE LOCATIONS & CABLE ROUTE ...............38
APPENDIX B - RESPONSIBILITY FLOW DIAGRAM 39APPENDIX C - PROJECT DIARY 41
APPENDIX D – WIJSLIFT 6 & SEACORE DRILLING RIG ................43
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APPENDIX E – LIFTING OF THE MONOPILE .....................................45
APPENDIX F – CROSS SECTION OF CABLE........................................47
APPENDIX G – 2.0MW BLYTH OFFSHORE WIND TURBINE ..........49
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APPENDIX A NOT AVAILABLE ELECTRONICALLY
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2 INTRODUCTION
2.1 Background
The wind farm off the coast of Blyth, Northumberland, is the first offshorewind farm built in the United Kingdom. Two 2 MW (see Appendix G for ascale diagram) wind turbines have been installed at a distance ofapproximately 1km from the coast, in a water depth, at low tide, of about 6mwith a tidal range of approximately 5m. The completed project is the first inEurope to be exposed to the full force of the North Sea weather as well as asignificant tidal range. The site is subject to breaking waves.
The site location is on a submerged rocky outcrop. Each wind turbine hasbeen erected onto a steel pile (monopile) that was drilled and grouted into therock. The 3.8m diameter holes for the pile were drilled from a jack-up barge(the Wijslift), and the pile lifted off the supply barge by the crane on the jack-up barge and allowed to sink into the drilled socket. The monopile was thengrouted into position and allowed to cure. When it had been confirmed thatthe monopile was secure in the hole, the sequence of erection was tower,nacelle and finally the rotor with the three blades attached.
Before any work could commence on site an FEPA (Food and EnvironmentProtection Act) licence had to be granted from MAFF (Ministry of AgricultureFisheries and Food) as the installation involved disposing of the drilling spoilinto the sea. Part of the conditions for this licence were that some divingsurveys had to be carried out before and after installation to review anypotential impacts on the marine flora and fauna in the surrounding area. Thefirst dive survey was executed in June 2000, before any work commenced.This gave the marine biologists their initial data. They then suggested toMAFF that the post dive survey should not be carried out until June 2001 toenable any impacts to be monitored at the same stage of seasonal growth asthe pre-construction survey. This would allow an accurate before and aftercomparison and was therefore agreed and approved by MAFF.
The site has the benefit of all the consents required for the installation of theturbines. An Environmental Assessment was produced and detailed siteinvestigation studies were carried out and evaluated in order to complete thedetailed design of the structure.
The Blyth Offshore Wind Farm has been developed by Blyth Offshore WindLimited (BOWL), a joint venture company between Powergen Renewables,Shell, Nuon and AMEC Border Wind. The diversity of experience and skillswithin these organisations has been brought together to pioneer the firstproject in what promises to be a new and exciting industry for the UK.
Powergen Renewables is a 50/50 joint venture between Powergen andoffshore oil services group Abbot. Shell Renewables is one of five corebusinesses for the Shell Group, established to develop commercialopportunities in renewable energy. Nuon is a large Dutch utility and is the
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largest operator and developer of renewable energy projects in theNetherlands. AMEC Border Wind develops and operates innovativerenewable energy projects and was behind the UK's first semi-offshore windfarm at Blyth Harbour.
A flow diagram showing the different responsibilities of the companies isincluded in Appendix B.
Two minor contracts were placed by BOWL.1. For Shell to act as project manager2. For AMEC Border Wind to provide project services
The contracts for this project were managed by AMEC Border Wind. Thisincluded the supply and installation of the monopiles, the supply andinstallation of the wind turbines and the laying and connection of the cables.
The contracts were:
• Global Marine – supply, installation & commissioning of cable (hook-up to free issue switchgear)
• AMEC/Seacore – supply of foundation monopiles, transportation andinstallation of wind turbines. (including lifting of towers etc.)
• Vestas – supply of turbine (towers, nacelles & rotors)After the installation by AMEC, Vestas will commission the turbines.Normal commissioning period is one to two weeks, at Blyth it will bethree months to fine tune the turbines because it is the first time thatthese machines have been used offshore.
There were two types of interface between the three main contracts
1. Information flow2. Physical Interfaces
Safety Procedures and Quality Assurance were also interfaces that had to bemanaged.
The turbine was designed and manufactured by Vestas, which included thetower, nacelle, hub and blades.
The two-piece tower was manufactured at the Vestas tower manufacturingfacility in Varde, Denmark, the nacelle and hub were assembled at Vestas V66manufacturing facility in Ringkøbing, Denmark and the blades weremanufactured at Vestas blade manufacturing facility in Lem, Denmark. All ofthese parts were transported in special containers from the various sites to theport of Esbjerg and then shipped to the AMEC facility on the River Tyne,Newcastle.
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The AMEC facility (Howdon Yard) on the River Tyne was used as the storagefacility both before and during the installation of the wind turbines. TheHowdon yard operates as a supply base which not only includes on sitestorage, but also permanent on site cranes that can lift large items of plant andequipment on and off vessels from the quayside. The location of the yardenabled delivery and transportation of materials to be by either road or sea.The yard is situated approximately 23km from the site location at Blyth whichequated to 2 hours travelling time for the loaded barge to sail from theHowdon yard to the site at Blyth.
Prior to installation the turbines were delivered to the Howdon yard and storedthere until they were needed, as well as the switchgear and basically any itemsof equipment or plant that were needed during installation and commissioning.The Wijslift was also based at the Howdon yard and the modifications thatwere needed to the vessel were completed while berthed at the yard.
The logistics and craneworks for the installation of the turbines were handledby AMEC Marine, but the fitting of the turbine parts was carried out by Vestasservice engineers.
After the installation of the first turbine a review meeting took place withVestas, AMEC Marine and AMEC Border Wind to go over the installationevents. This evaluated how each part of the installation had progressed, wherethere were any deviations from the plan, what improvements could be made,what (if any) safety issues occurred and finally what action was requiredbefore the installation of the second turbine. The changes had to be discussed,agreed on and implemented quickly as the installation of the second turbinewas time critical.
Included in this report are both of the methods used for the installation of thefirst turbine and then the different methods that were used for the secondturbine.
The diary of the installation is in Appendix C.
2.2 Aims & Objectives of this Report
The principle aim of this report is to appraise the practical aspects ofinstallation and commissioning of the offshore wind farm. The constructionand installation activities of the project were monitored and reviewed by theproject team to enable recommendations for future larger projects to be made.
This report particularly looks at how the project progressed against theconstruction and installation schedule with regard to weather conditions andoperational procedures. The document not only describes the methods ofinstallation, assembly and cable laying, but also reviews the effectiveness ofthose methods including any difficulties that were encountered and thesolutions that were found.
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2.3 Equipment Used
• Coastal Explorer – this small survey vessel was chartered by GlobalMarine for use during the cable installation operations, it allowed theinstallation to proceed outside the restricted weather criteria of theGlobal Marine modular cable barge.
• Andre B – was the spud leg dredger used to dig the cable trench acrossthe river and was capable of working in wind speeds of 17-25 knots,force 5-6. (Spud legs on a vessel are legs that are lowered onto the sea/river bed. Lowering the legs lifts the vessel up by a small amountwhich results in increased stability of the vessel.)
• Indus – this was the tug that was used to manoeuvre the Andre B andalso to tow the ZH7 barge to and from the disposal ground and theriver.
• ZH7 – the barge / pontoon that was used to carry the dredged materialfor disposal.
• RHIB – rigid hulled inflatable boat that was a fast boat used for crewtransfer and general operational support.
• Wijslift 6 – a six leg jack up barge owned and operated by AMECMarine, equipped with a 250t capacity crane equipped with a 54mmain boom and a 12m fly jib. (Jack-up legs lowered on to the sea bedto raise the vessel above the water.)
• Atlas – the transport barge, a 55 x 22m dumb barge equipped withthree 50T spud legs for mooring the vessel.
• D H Bravo – the vessel used to control the spoil disposal operation,transfers of plant and materials locally and assist with bargemovements.
• Safety Boat – the Wijslift 6 is equipped with a 22ft RIB rescue boatpowered by an inboard diesel with twin water jet unit. This is storedon deck ready for rapid deployment by the hydraulic deck crane.
• Topcat & Cambois – support vessels to transport personnel to and fromthe site and also used to standby when certain operations were takingplace.
• Seacore Teredo 40 (T40) – a pile top/shaft drilling machine capable ofdrilling up to 6m diameter sockets. It can provide 30t continuous and40t intermittent torque to the drill string/ drill bit and up to 150t of pullback. Two Seacore Volvo ‘Hushpack’ hydraulic power packs powerthe T40.
• Drill Casing – the assembly had three parts; a 17m long x 3720mmprimary conductor tube, flange bolted at the bottom to a 1.5m long x3780mm gripper can. A sacrificial casing shoe with reinforced, sawtooth profile toe, sleeves into and was held by pneumatic grippersinside the gripper can.
• Grout – CMS Pozament 80/20P high strength polymeric grout wasused to grout the annulus between the rock and the pile. The groutcontains a long chain organic polymer to resist wash out or dilutionand has a short time period between initial and final set. It wastherefore suitable for underwater grouting applications.
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• Pump unit – the grout was mixed and placed using Seacore’s twin potcolloidal mix/pump unit. The unit comprised two high shear colloidalmixing tanks above a single paddle wheel agitation holding tank. Thegrout was placed by two helical drive mono pumps, which drewdirectly from the bottom of the holding tank.
• Spoil pumps – spoil material was pumped by two Pegson VS150 HF4diesel pumps. They were capable of pumping 500m3/hr to a head of63m and could accommodate particles up to 98mm diameter in a water/ solids ratio of 12.5:1
• Spoil Disposal Pipeline – was a 280mm outside diameter, 200m longMDPE spoil disposal pipeline that transported the material to a droppipe with a sinker weight depositing it outside the exclusion zone.
• Monopiles – 33m long, 3.5m diameter, 120t weight. They weredesigned by Vestas and LIC, whilst the engineering and manufacturewas completed by Watson Steel.
2.4 Sea Conditions
To define the sea limits 0.5m marks were painted on the legs of the Wijslift inview of the Atlas so that the sea state can be measured, whilst the on site thewind speed was measured on the anemometer on the jib of the Wijslift.The limiting factors were set so that grouting operations could only take placeduring wind speeds of 10m/s or less in a swell of 0.5m or less. Liftingoperations could only take place on site in wind speeds of 8m/s or less and in aswell no greater than 0.5m.
For lifting operations to take place at the Howdon yard the limits were set towind speed of 10m/s or less and also authority had to be received from theharbourmaster before anything could be moved from Howdon to site offBlyth.
For personnel transfer to and from the Wijslift the main access ladder could beutilised at all states of the tide up to a deck level of +14.0m.
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3 INSTALLATION
The installation of the offshore wind farm is described in detail throughout thissection of the report describing the different activities and stages that wereinvolved. When it came to planning and scheduling some of these activitieswere grouped together under one task heading in the project plan.
3.1 Planning and Scheduling
Monopile installation in the project plan actually covers all of the activitiesdescribed in 2.2, 2.3 and 2.4. The time scheduled for the installation of themonopiles was originally 15 days in total, 7.5 days for each pile. In actual factit only took 6 days to install the first monopile and then 7 days to install thesecond. The second installation took slightly longer as the second monopilewas 2m longer than the first, so obviously the hole had to 2m deeper whichadded to the drilling time. This was a result of ground investigations at thesite revealing a different formation in the rock at the second location. In effectthe installation of the monopiles went according to plan.
After the monopiles were installed the plan was to carry straight on with theinstallation of the turbines. This task was initially scheduled for 2.5 days foreach turbine. In reality after the monopiles were installed the weather tookanother turn for the worse and storms hit the site, the result being, themonopiles were installed for a period of two weeks before the turbineinstallation could be attempted.
The first turbine took 13 days to install but only 4 of those days were workingdays. The tower sections went on in the first 2 days, the nacelle was installedthe following day and then a further 9 days were spent waiting for suitableweather and sea state to bring the rotor out to site and lift it into place. Whenthat did happen it took 1 day to transport the rotor from the AMEC facility onthe Tyne to the site and then to lift and install it.
The second turbine installation only took 5 days. The tower and nacelleinstallation was shortened from 3 to 2 days by changing the method ofinstallation as described in 2.5. As with the first turbine installation suitableweather conditions were needed to transport and install the rotor, but in thiscase the waiting period was only 2 days as opposed to the previous 9.
Once again this highlights just how important good weather and sea conditions(low wind and swell) are for offshore installations.
3.2 Casing Installation & Socket Drilling
The monopiles had to be installed into drilled sockets as the site was on hardrock, too hard for the piles to be driven in. The drilling machine that was usedfor this project was the Seacore Teredo 40 (T40), which was a pile top/shaftdrilling machine as shown in Fig. 1. The T40 was powered by two hydraulicpower packs.
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Fig. 1
Underneath the T40 a tubular steel guide was attached to act as upper supportfor the conductor and casing shoe assembly. A drawing of the Seacore drillingrig on the Wijslift 6 vessel is in Appendix D. The conductor and sacrificialcasing shoe assembly assisted in keeping the drill string and the socketvertical. The assembly consisted of a conductor tube, flange and gripper canand enabled a ‘diver free’ operation of disconnecting the conductor from thesacrificial casing shoe on completion of the socket drilling.
A smaller drill bit was used initially to drill a centralising hole for theconductor assembly installation before the 3800mm diameter drill bit wasused.
When the Seacore driller / engineer was satisfied with the socket levels thedrill bit was pulled off the socket bottom. The conductor and gripper canassembly were pulled back up through the casing guide. The T40 wasmanoeuvred away from the socket location and the socket was then ready forthe pile installation.
The were approximately 14 people involved during this operation, includingthe crew of the Wijslift 6, the Seacore personnel, a supervisor and a projectmanagement representative.
3.3 Spoil Disposal
A 200m long x 280mm diameter MDPE spoil disposal pipeline transported thepumped material to a drop pipe with sinker weight depositing outside the
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exclusion zone. The reason for the use of the spoil pipe to remove the spoilfrom site was to ensure that the existing lobster holes on the exposed rockhead did not become blocked. A licence and approval had to be obtained fromthe Ministry of Agriculture Fisheries and Food to authorise the deposit ofsubstances in the sea as part of the Food and Environment Protection Act1985.
The hose was assembled in 11.5m lengths with flanged ends. Each lengthincorporated one or two closed cell polyethylene flotation collars, each collarhaving a net buoyancy of 250kg. The collars enabled the floating hose tomaintain positive buoyancy at all times during the pumping operation. Fig. 2shows the spoil pipe in use as the drilling took place for the southern turbine.
Fig. 2
A specially designed and reinforced container positioned directly underneaththe T40 spoil exhaust outlet acted as a buffer for the airlifted spoil prior tobeing pumped along the floating hose to outside the exclusion zone. Theairlifted spoil material was highly aerated by the time it reached theatmosphere, so the 20ft container also ‘de-aired’ the water for more efficientpumping.
The spoil material was pumped by two Pegson VS150 HF4 diesel pumps. ThePegson pumps were positioned on the deck of the Wijslift 6 drawing directlyfrom the spoil container, through two 6" Bauer hoses. The pump outlets fedinto a 10" steel manifold which was connected to the 200m long floatingdisposal pipeline.
During the drilling process the airlifted spoil material was collected in thebuffer container and pumped along the floating hose for near seabed disposaloutside the exclusion zone. A sinker weight on the end of the drop pipe
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helped with the positioning of the flexible hose and enabled distribution of thespoil material on the seabed.
During the drilling operations the support vessel operated 24 hours to monitorthe spoil disposal system. The vessel moved the end of the pipeline at regularintervals to maintain even dispersion of the spoil. No formal records of thisoperation were kept.
3.4 Monopile
At the AMEC facility (the storage yard) the monopile was loaded onto theAtlas spud leg barge that was moored alongside. Once the hole had beendrilled for a monopile it was delivered to site (from the storing yard) by theAtlas barge. The monopile was then lifted off the barge, positioned in the holeand grouted in place.
3.4.1 Installation Operational Requirements
At the site of the wind farm the lifting operations for the monopile werelimited to and could only be carried out when the wind speed was 8m/s or lessand the swell was no greater than 0.5m. Restrictions also applied at thestoring yard when lifting the monopile onto the Atlas barge. There the windspeed had to be no greater than 10m/s.
The wind speed at site was measured on the Anemometer on the jib of theWijslift, whilst the swell was measured against a marked up leg. A log of thewind and wave conditions was kept as soon as the Wijslift was on station.
In order for the Atlas barge to travel from the storing yard to site, authorityhad to be received from the harbourmaster and a storm haven had to be madeavailable in Blyth Harbour.
3.4.2 Loading Monopile Sections onto Atlas
When the monopile sections were being loaded onto the Atlas barge, it had tobe moored alongside the quay and secured with mooring lines. The spud legswere also dropped and the preparations for sea fastening were carried out. Thelifting slings were then attached to the monopile and when the weather wasdeemed suitable (see 2.3.2) the sections were placed and secured onto the deckof the Atlas and then the sea fastenings were completed as shown in Fig. 3.
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Fig. 3
Once the socket drilling had been completed the T40 was manoeuvred out ofthe way of the socket location. An open rock socket then existed in the seabedwith the sacrificial casing shoe installed.
The pile seating lugs positioned at the pile toe were adjusted in accordancewith the final level of the socket bottom. All of the necessary hoses, strops,survey aids and the like were assembled on to the pile ready for pileinstallation.
At site the Wijslift jib was brought into position over the monopile and asingle wire hook on the main jib head was used to find the centre of gravity.Once the centre of gravity had been located the sea fastenings were thendetached.
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Fig. 4
For both monopiles the units were lifted and rotated until they were suspendedvertically (as shown in Fig. 4) and then presented over the centre of the rocksocket and lowered through the pile gates into the water. (Appendix E showsa drawing of this procedure). The pile gates offered guidance to the pile as itwas lowered into the top of the rock socket, sufficient sea water was pumpedinto the pile to ensure it sank into the socket. Pile lowering continued until thepile ‘feet’ were fully seated on the socket bottom. The pile position,orientation, vertically and level were checked from the shore survey stationsand adjustments made as necessary. Following confirmation of the pilesurvey, the pile was flooded to a designated level (for grouting operations) andthe crane released.
3.4.3 Grouting
A high strength polymeric grout was used to grout the annulus between therock and the pile. This type of grout was used as it contains a long chainorganic polymer to resist wash out or dilution and has a short time periodbetween initial and final set, and is therefore suitable for underwater groutingapplications.
The fresh water needed to mix the grout was supplied from the Wijslift ballasttanks, which were filled at the quay prior to sailing. Pile grouting wasundertaken as a continuous staged operation through a series of integral grouttubes that were installed in the pile during its fabrication. Each pile wasgrouted in four stages. The first stage pumped grout along two pipes throughthe base of the pile. The following grout stages two, three and four pumpedgrout through pairs of pipes running down the inside of the pile diametricallyopposite and terminating through the side of the pile.
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Grout migration up the rock socket / pile annulus was monitored by a groutprobe deployed down the next grout stage pipes. Once the probe detects groutat the bottom of the next stage grout pipes grouting operations were suspendedbriefly and the feed hoses disconnected from the last completed stage andreconnected to the next. This operation was continued until the groutoverflowed at the top of the annulus onto the seabed concluding pile grouting.
The pile gates remained in place providing lateral support to the pile until thegrout maintained its Pile Release Strength for up to 12 hours.
During the grouting operations grout cube samples were taken for each groutstage. 15 cubes were taken per monopile for crushing at the following times:
• 3 @ 24 hours• 3 @ 3 days• 3 @ 7 days• 6 @ 28 days
Extra cubes were taken at the early stages of the grouting operation so thatearly Ultimate Compressive Strength results could be obtained using an onboard portable crushing facility. The cubes listed above were maintained ondeck in a water tank until they were transferred to a laboratory near Newcastle.It was the cube test results that proved when the grout had reached its pilerelease strength.
The same personnel were involved in the grouting procedure as carried out theinstallation of the monopile. All in all the two operations combined involvedapproximately 20 people, made up of AMEC Marine and Seacore personnel.There were various people who travelled out to the site throughout theoperations to see what was involved, but they were there purely as observersand therefore have been discounted from the number of people actuallyinvolved.
3.5 Tower Installation
At the storing yard the Atlas was moored alongside the quay edge and securedwith mooring lines. As with the monopiles the spud legs were dropped andpreparations made for sea-fastening. The switchgear, tower sections andnacelle were individually lifted from the shore side onto the Atlas and the sea-fastenings completed. (See 1.4 for details of the sea and weather conditionsfor the lifting operations).
The loadings of the equipment were as follows:
Lower Tower 56500kgUpper Tower 29000kgNacelle Transport mode 72000kgNacelle Installation mode 63000kgTools Container 8500kgNacelle Transport frame 9000kg
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Cable Drum 2000kg
The switchgear, access platform, two tower sections and nacelle were carriedon the Atlas to site. When the Atlas reached the site at Blyth the first item tobe placed onto the monopile was the switchgear unit, but before anyequipment could be transferred a man had to be placed on the monopile toreceive the load.
Fig. 5
The access platform was lifted into position and secured before the towersections were installed. (Fig. 5 shows the access platform being guided intoposition). To lift the tower sections the Wijslift jib was brought into positionover each of the sections and the single wire hook was used to find the centreof gravity. Once the centre of gravity had been found the sea fastenings weredetached.
For the tower sections each unit was lifted and rotated until it was suspendedfrom the top end alone while a minimum of two tag lines had to be attached tothe extremes of the lift. (Fig. 6 shows one of the lower tower sections as itwas first lifted horizontally off the barge). The tower section was then broughtback over the Atlas deck with one metre minimum clearance to allow thebolted lifting shoe to be un-bolted and disconnected. The tailing blockcontinued to be lowered to leave the unit solely suspended below the headlifting beam. The tailing sling was either disconnected or raised above thebase of the tower unit.
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Fig. 6
For the second tower installation the Wijslift was brought back into theharbour where the lower tower section and nacelle were loaded onto theWijslift to be taken out to the site of the northern turbine and thereforeeliminating lifting those turbine components from being lifted off the Atlasbarge. (This installation method was a revision to the original and wasdecided upon after the project team reviewed the first turbine installation andthe problems that had been encountered). As the Wijslift was jacked up abovehigh water those lifts could take place in swell conditions that otherwise wouldhave prevented the lifts from going ahead had the components been on theAtlas. This resulted in the second tower installation being a lot quicker thanthe first as it eliminated one of the limiting factors, sea state / swell.
At each tower connection at least 40 bolts had to be in place and the torquesequally spread around the third points of the circumference before the cranecould be disconnected from the load. When the tower base was secured a manclimbed the tower to release the lifting equipment from the top of the towersection. Likewise when the upper section of the tower was being installed twomen were in place in the top of the lower section to bolt the two sectionstogether. (Fig. 7 shows the top tower section being aligned to the lowersection). Then when sections were joined and torqued together the men had toclimb to the top of the tower to release the lifting equipment.
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Fig. 7
When placing the Nacelle particular attention had to be paid to wind and seaconditions. The nacelle was lifted together with its transport frame onto theWijslift deck so that the crane operator on the Wijslift could be sure of enoughheight and clearance by lifting straight from the deck of the Wijslift up to thetop of the tower. (The Wijslift had been previously been jacked up and wastherefore quite a bit higher than when the nacelle was lifted from the deck ofthe Atlas barge). The transport frame provided protection as it left the floatingcraft. Once on the Wijslift the nacelle was un-bolted from its transport framefor lifting into place. Fig. 8 shows the nacelle in place on the top of the tower.
Fig. 8
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All personnel that were working at height within the Tower during assemblyused the harnessing arrangements provided within each tower section.
3.6 Installation of the Rotor
The assembly of the rotor was completed at the storing yard. Once completedthe unit was lifted from the shore onto the Atlas barge and sea fastened inplace before being transported to site and securely positioned next to theWijslift barge. The site surface conditions were the same as for the lift of thetower sections (see section 2.3.2).
3.6.1 Loading Rotor onto the Atlas
The rotor was the last item to be placed on the barge. The barge had to beturned prior to the installation in order to avoid any possible damage to theblades, two of which overhung the edge of the barge.
Once the rotor was secured on the deck the support that was needed under thethree blades had to be built up. (This was used to stabilise the blades fortransport.) The blades were rested in wooden frames and edge protectors wereinstalled prior to any strapping of the blades.
The tip packing was placed in position on the deck and the sea fasteningchains were prepared at the hub securing point. The lifting slings were thenattached to the rotor assembly, it was then lifted together with the nose coneonto the barge and the sea fastenings were completed. The tag-lines were thenattached to each tip and the barge sailed in this condition. Fig. 9 shows therotor as it was finally lowered onto the barge.
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Fig. 9
The assembled rotor on the deck of the Atlas barge was:
Total weight 24000kg
3.6.2 Lifting the Rotor into position
The Atlas barge arrived on site at Blyth with tugs controlling its position. Theposition was fixed using anchors controlled from the Atlas barge. The WijsliftFly jib was brought into position over the load and the tailing crane wasattached to the Tailing Blade tip. The sea fastenings were then detached fromthe blades.
The rotor was positioned with the flange uppermost. Using the Wijslift cranethe lift started, then the nose cone was wheeled into position under the hub.Securing bolts were fitted into the cone apex before the cone was released.
A tandem lift was used to move the completed rotor assembly from the deckof the Atlas spud leg barge, onto the nacelle of the rotor tower. The rotor waslifted from a face down position on the Atlas, to a near vertical position next tothe tower as shown in Fig. 10. The blades were rotated past 90 degreesthrough the vertical position. The rotor was then secured to the tower and thelifting apparatus and the tag lines removed.
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Fig. 10
The hub was released from the hook and the line and blade packing wasreleased, but the hub could not be un-pinned and rotated until it had beenturned in plan to be running parallel with the face of the Wijslift. Fig. 11shows the rotor finally installed.
Fig. 11
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3.7 Installation of the High Voltage Turbine Cable
The installation had to be done before the Wijslift could move due to the factthat the generator on board was needed to operate the nacelle service crane asthere was no electrical power in the turbine at that time. The cable drum waslifted in a frame that was then mounted on to the access platform. The nacelleservice crane was used for pulling the cable inside through the door and alsoduring the installation.
The cable was wound around the cable loop in the lower part of the top towersection. From the cable loop down the HV cable was fastened with cablestrips to support for the leader. The cable was then fed down below the lowerplatform of the tower bottom section and into the HV switch. The signal andsupply cables were fastened with cable strips to the HV cable all of the waydown together with the protective conductors. Protection tubes for the cableshad to be mounted at platforms and fences to reduce the risk of contact withswinging cables.
As with the installation and the grouting of the monopile, the same teams ofpeople were involved with installing the turbine, from the access platform tothe rotor and landing of the tower cable. There were 15 people working onsite during the turbine installation. The operations being directed by theVestas personnel and the AMEC crane operator.
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4 CABLE LAYING
The scope of work for the installation of the power cable between the twooffshore wind turbines and the mainland included:
1) Procurement of the cable2) Mobilisation of installation vessel3) Loading of the cables4) Diver swim survey across the harbour and of site of the turbines5) Installation of the duct across the harbour mouth6) Installation of the cable across the harbour mouth7) Installation of the cable between the offshore wind turbines8) Installation of the cable between the southern turbine and the
breakwater9) Reinstatement of the beach10) Demobilisation of the installation vessel
The route of the cable is shown in Appendix A.
The submarine cable used for the project was 70sqmm EPR Double WireArmour with 16 fibre optic package. A diagram of the cross section of thiscable is shown in Appendix F.
4.1 Optical Fibre Package
The optic fibres were contained in a seamless, laser welded, hard drawnstainless steel tube filled with a thixotropic compound. The fibres aresubmarine telecommunications grade, single mode compliant. The cable loadelongation performance is crucial to the fibre long term performance andeffective service life. Therefore the optic package was of a loose tubeconstruction ensuring that the fibres see no strain at the designated workingload.
4.2 Planning and Scheduling
The task names used in the project plan do not directly correspond theactivities described in this section. As with the installation of the monopilesand turbines some of the cable laying activities were grouped together underone task name for planning purposes.
In the original plan the duration for cable laying was sixty days. In actual factthe cable laying process took 3.5 months. However, as with the installation ofthe turbines not all of this time was working time. The delays in installing theturbines had a ‘knock-on’ effect on the cable laying activities i.e. the cablecould not be laid between the turbines or from the turbines to the beach untilthe turbines had been installed and the vessels used during the installation hadmoved off site.
When the cable lay commenced between the turbines and from the southturbine to the beach it took 5 days as planned. The cable was laid from the
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south turbine to the beach first, but again due to bad weather and high seas thecable lay between the turbines could not be done until 2 or 3 days later. Thisparticular task was originally scheduled to only take 1 day and ended uptaking 3 days as the sea state was constantly changing which disrupted thediving operations.
The cable lay across the river and the dredging work that proceeded it alsotook longer than planned. The planned duration was 15 days when it actuallytook about thirty days. Again this was not thirty working days. There wereapproximately 7 to 10 days of ‘downtime’ when the crew of the dredgercarried out repairs to their hydraulic system and also changed buckets thatwere broken digging the rock out of the river bed. The working time wastwenty days, which is still longer than planned, but was due to the trench andducts backfilling before the cable could be pulled through.
The weather was still a big problem during the cable laying activities eventhose that were being carried out onshore. For example there were occasionswhen work could not be carried out on the pier as the wind was too strong. Asa result the plan was constantly shifting and it almost ended up being a case ofcompleting jobs and parts of jobs as and when they got the chance.
To summarise the cable laying was held up initially by the delay in the turbineinstallation and then later by the weather and also unforeseen conditions (e.g.trenches backfilling etc.). The following sections describe in more detail theactivities that took place.
4.3 Beach Preparatory Work
Site perimeter barricades for the beach work area were provided throughoutthe operations for public safety. This was due to the fact that tension on thecable could be experienced on the beach and an exclusion zone was requiredin the interests of public safety. A clear path of the cable pull line was created.Fig. 12 shows the cable trench on the beach disappearing into the sea.
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Fig. 12
Liaison was established with the Harbour Commission and obviously theHarbour Master in order to advise them of operations and provide them withinformation.
4.4 Vessel
The Coastal Explorer was chartered by Global Marine Systems Limited to beused throughout the cable laying operations between both turbines and alsofrom the southern turbine to the pier. The cable handling equipment wasloaded on board and bolted into place. Once the vessel had been mobilised,the cable drum was loaded on board and installation commenced.
4.5 Navigational Aids
Navigational, tracking, monitoring and recording systems consisted of thefollowing:
1 x DGPS receiver, which provided a “Helmsman’s display” and had adata logging feature that recorded the position of the installed cable.
4.6 Cable Landing
The installation vessel was moored in the close to the base of the SouthernTurbine. The cable end was then passed up the “J-Tube” via a short
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messenger line, utilising a small winch or hydraulic Tirfor. Once the requiredamount of cable had been installed and secured into the turbine, the cable laycould commence.
When the installation vessel approached the shore, the cable end was passed tothe beach team via divers (wading depth), who then pulled the remaining cableonto the beach, until the required amount of the cable was ashore.
4.7 Diving Operations
The diving operations were carried out both safely and efficiently. It wasimperative that all diving operations were thoroughly planned, briefed andexecuted in accordance with all appropriate diving regulations. (The CoastalExplorer was also used as the dive support vessel.)The works included:
• Surveying proposed shore end route• Assisting with the pulling rope• Removing the cable floats• Surveying the as laid cable (where necessary)• Supporting cable lay and burial operations• Attachment of Uraduct (product name for ducting used to give extra
protection to the cable where required).
The diving team were under the control of a suitably qualified DivingSupervisor who had direct overall control, and responsibility for the safety ofthe diving team. However, in order for diving operations to commence, and tocontinue, authorisation was required from the Diving Supervisor, the OffshoreSuperintendent and the Beach Master (or their appointed Deputy). Divingoperations would have ceased forthwith if, at any time, for operational orsafety reasons authorisation had been withdrawn by one of these people.
4.8 Cable Lay Operations between the Northern & Southern Turbines
When permission had been received from the shore that the lay couldcommence the Offshore Superintendent took over responsibility for the cablelay. Once all the pre checks had been completed the vessel moved to theNorth Turbine and moored up at the base of the turbine. A messenger line wasrun up the “J-Tube” and a small winch or hydraulic Tirfor was installed at thetop of the “J-Tube”. The cable was then hauled up the J-Tube via themessenger line. Once the required amount of cable had been hauled up thecable was then secured inside the turbine tower. The cable that was laidbetween the two turbines and also from the southern turbine to the beach waslaid directly onto the sea bed. Fig. 13 shows the cable laying vessel inoperation between the two turbines.
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Fig. 13
The cable was paid out from the cable drum, controlled by the powered cablestand, via the overhead cable roller quadrant and cable pathway. The cablelead was visible at all times from the deck vessel.
4.9 Cable Lay Operations Across the River Blyth
Due to the changes in burial criteria (see Section 5.2), Global Marine SystemsLtd researched the use of a suitable dredger to remove the 2m of mudoverburden and to cut a trench into the bedrock. A cross section of theharbour was drawn up showing the depth of burial that had to be achieved. Aspud leg dredger was mobilised complete with a built in dredging arm that wasable to operate throughout most of the tidal range and the spoil was loadedonto a pontoon and dumped at the Port of Blyth’s dedicated spoil dumpingarea. Fig 14 shows the dredger in operation with the pontoon alongside. Anextension to the Blyth Harbour Commission licence for the deposit ofmaterials at sea was obtained for the duration of the river dredging operations.
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Fig. 14
As the trench was excavated a duct was installed. It was positioned into thetrench by divers and weighted so that it would sink. At the breakwater theduct met with another directionally drilled duct, and as a manhole hadpreviously been excavated on the harbour wall it allowed the cables betweenthe river and offshore sections to be terminated.
The cable for the harbour crossing was delivered to site on a drum. This drumwas set up on the shore / quayside and pulled through the duct to the manholeutilising a winch.
4.10 Weather Contingencies
The majority of the cable laying operations were governed by the weather ormore to the point reliant on “good” weather. Prior to the start of eachoperation and in addition to the daily weather forecasts received duringoperations, long term weather forecasts were also obtained from a professionalweather service to cover the period of operations. To ensure the safety ofpersonnel and the security of the cable, work was never started if bad weatherwas forecast. Similarly when the weather proved to be different to thatforecast and weather changed for the worse all work was stopped andequipment and personnel made safe. Specific weather conditions were notlaid down for each operation, offshore superintendent and the dive supervisorhad the training, knowledge and expertise to interpret weather forecasts andswell to know in what conditions the work could be carried out.
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4.11 Daily Reporting
A report was submitted daily, starting from the day of the departure from themobilisation port and finishing on arrival at the demobilisation port. The dailyreport contained the following:
a) time, date and number of the reportb) weather conditions experienced during the preceding 24 hoursc) geographical position of the vessel at the time of the reportd) summary of the work performed during the preceding 24 hourse) summary of the planned work for next 24 hoursf) time spent on effective work during the preceding 24 hoursg) weather downtimeh) vessel / equipment downtime during each 24 hour periodi) summary of plant installed and burial performancej) any other pertinent information about the operation and progressk) endorsement of the report by the Customer’s Senior Representative
During the cable laying operations the numbers of people that were directlyinvolved varied from stage to stage, i.e. vessels and divers were used for theoffshore cable laying as opposed to one or two cable hands laying the cableinto the onshore switchroom. There were on average 10 people + 1 supervisorworking throughout the cable laying operations.
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5 COMMISSIONING
There were various stages to commissioning the wind farm. Initially Vestashad priority over access to the turbines and a procedure was put in place whereany personnel going out to work on the turbines had to complete a permitstating exactly who was going out, what work they were going to do and alsogiving mobile phone numbers for communications purposes. Then when theyreturned back to the site office the permit had to be signed off to say that thework was completed for that day.
During this period of time the marine lanterns and foghorn for navigationalpurposes had to be fitted and the cable jointing team had to have access toterminate the power cable onto the switchgear in each tower. Once the powercable terminations were completed both in the turbines and onshore in theswitchroom and the installation was tested the Distribution Network Operatorwas then able to energise the wind farm i.e. connect the wind farm to the grid.
At this time the communication system was completed. This required thefibre optic cores to be terminated in each turbine and also in the control roomonshore. Once the terminations were complete the various items of equipmentneeded to send and receive signals down the fibres were connected and testedto enable the turbine controllers to be accessed remotely from the controlroom. (The turbines can be checked using the onshore computer as well asstopped and restarted if need be.)
Even though the wind farm now had power the final commissioning tests andgeneration could not take place until the protection engineer from theDistribution Network Operator had witnessed the testing of the G.59protection relay in each turbine. (This relay disconnects the wind farm in theevent of a problem with the grid.) Once the tests were complete the finalcommissioning of the wind turbines could take place, including a 240 hourcontinuous generation test.
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6 ISSUES
6.1 Blade Lifting Procedure
The initial procedure that was discussed for lifting and installing the bladeswas to lift the blades using a horizontal method and installing them separately.
The idea was to use a large clamp about 3m in length that would be attached tothe crane hook. Before the blades could be installed the nacelle would beinstalled with the hub attached. Inside the nacelle the coupling between thegenerator and the gearbox would have to be disconnected and a hydraulicmotor connected to the gearbox to enable the hub to be turned for the bladesinstallation.
The clamp was to be attached to each blade in turn about its centre of gravity,then the blade would be lifted up horizontally and offered up to the flange onthe hub, bolted on and the clamp released (via remote control). Once thatblade was in place and the clamp removed the hub would be rotated so that thenext flange was in line for the next blade to be lifted horizontally. The processwould then be repeated for the third and final blade.
There were three main problems that prevented this procedure from beingused:
1. Vestas wanted to test this method of lifting and installation on landbased projects first, but those projects were delayed and put back untilthe point where if testing had gone ahead we would have been into theplanned installation dates.
2. There were delays with the clamp manufacturer which could haveresulted in only one clamp being made and no back up
3. There were also similar problems with the hydraulic motor for thenacelle and that there would be no back up and also the motor was veryheavy and difficult to manoeuvre up to the nacelle and back downagain once the blades had been installed.
The solution to the problems posed by the initial blade lifting and installationprocedure was to use a completely different, yet tried and tested method asdescribed in Section 2.3 in this report.
6.2 Cable Route Across the River
A change to the channel depth resulted in change of method of laying cable.
Initially it was understood that the cable had to be buried 2m below the currentdredged depth of the river so the initial plan was to prepare a deep trenchacross the river below bed level and bury the cable in the trench without usingany ducts. However, Blyth Harbour Commission actually required the cableto be buried under the River Blyth at a depth of 2m below the maximum
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dredged depth and as a result a change was made to the proposal. Differentmarine plant was now required in the form of a dredger which would be usedto dredge down below the maximum dredged depth. As the requirement wasnow to go below the bedrock the new proposal was to excavate a shallowertrench in the bedrock of the river bed, lay ducting, then pin the duct to thefloor of the trench and lay the cable through the duct.
Herbosch-Kiere was the company who supplied the spud leg dredger to assistwith the cable laying activities across the river Blyth. All dumping wascarried out in accordance with an extension granted to Blyth HarbourCommission dumping licence to cover this operation, therefore Blyth HarbourCommission had to be kept fully informed.
When dredging commenced there were no problems removing the silt andmud, but when the dredger reached rock it was a lot harder than they had firstthought. This caused several problems, mainly breakages of dredgerequipment which resulted in delays as the equipment had to be replaced.
Global Marine Systems and the dredger crew found that they had reached therequired depth fairly quickly in some parts of the river and not in others, butacross the river they hit what they classed as bedrock and proposed that theydig a metre below this level and that would be sufficient depth to bury thecable at. This required approval from Blyth Harbour Commission.
The Harbour Master and Port Engineer viewed the equipment that the dredgerwas using while they were working on the trench and this proved to them thatthe profile and depths that the dredger was reporting they had reached weretrue. When the dredger had excavated the trench across the river from the eastpier to the quayside the Harbour Commission went back on the dredger andfollowed the trench across the river agreeing the profile and depth and givingtheir dispensation on the original depth that they had requested for the fulllength of the trench. This immediately solved the potential problem of havingto bring in specialist rock breaking equipment.
6.3 Weather
The weather was always going to be an issue and could not be relied upon.Trying to arrange and plan a project so that installation takes place in certainmonths of the year, i.e. the summer months would hopefully reduce thepossibility of bad weather affecting progress.
This was initially the case for this particular project, but unfortunately (andunusually for that time of year) the weather took a turn for the worse and inparticular caused an increase in the swell.
As explained earlier in this document many of the installation procedurescould only be carried out in swell of 0.5m or less. The reason being that it wasunknown how the equipment being used would react in certain conditions.
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Even at low swell there is still a chance of “rogue” waves and the reaction tothese waves could have caused damage to the turbine items on the Atlas barge.
For instance if the load was taken on the crane and the crane started to lift apart of the turbine and all of a sudden a wave comes along that would lift thebarge, the barge would react, lift up and hit the bottom of the load, causingdamage to that part of the turbine. Cranes cannot move quickly and the hooksholding the load cannot get the load out of the way very quickly. (Soft slingswere used to try and reduce or prevent any damage to the turbine duringlifting.)
There were no solutions to the weather problems other than to constantlymonitor weather forecasts and have everything geared up and ready to gowhen a suitable weather window was available.
6.4 Installation Differences
When the first turbine was installed each component was taken to site on theAtlas barge and had to be lifted from the barge by the crane on the Wijslift.The Wijslift was jacked-up above the sea and was therefore stationary whilethe Atlas barge was moving up and down with the swell. Having realised thatthis was restricting lifting operations to times when the swell and wind werevery low and therefore causing delays, the decision was taken to do thingsdifferently for the second turbine installation.
The Wijslift was towed back to the Howdon yard where the lower towersection and the nacelle were lifted on to the Wijslift to be taken out to site.This resulted in those two components being lifted directly off the deck of theWijslift. As the Wijslift was jacked-up above high water those lifts could takeplace in higher swell conditions that otherwise would have prevented the liftsfrom going ahead had the components been on the Atlas barge.
As a result the second turbine installation happening in a shorter time frameand eliminated the issue of sea state and swell.
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7 IMPLICATIONS FOR FUTURE PROJECTS
The installation and commissioning of the Blyth Offshore wind farm hashighlighted many implications that should be taken into consideration forfuture offshore wind farms. The four major ones are discussed in more detailbelow, but in general terms future project teams should review their methodsand operations throughout the installation and take into account and act on anylessons learned.
Installing a larger offshore wind farm would not require any more personnelthan were involved on the Blyth Offshore project, if anything fewer peoplemay be needed if the pile foundations are driven in, instead of drilling andgrouting them in place. Fewer people are involved in pile driving operationsand it also takes less time to drive a pile foundation in than to drill a hole,install the pile and grout it in place. However, the other aspect to consider is iftwo lots of equipment (2 x crane barge and flat barge) were used thenobviously twice as many people would be needed and it would in theory takehalf the time.
7.1 Equipment
For future larger projects further offshore it would be preferable to have acrane barge that can jack up above the swell to lift and install the pilefoundations and the turbine components, and a flat barge that could also bejacked up during lifting operations, to transport the components to site. If thecrane barge and the flat barge were jacked up way above high water then all ofthe lifting operations would be static lifts, i.e. neither the flat barge or thecrane barge would be moving and would be independent of the swell,eliminating that as a major problem for the lift.
Another issue to consider with equipment is having enough accommodationon the barges for all of the personnel involved with the installation. Obviouslylarger sites are going to be further offshore and quite probably some distancefrom ports, which means that daily transfer of personnel will not be an option.The only solution to this would be to have the personnel stay on the barges onsite during the installation.
The barges used during the installation of the Blyth Offshore wind farm werenot self-propelled and had to be towed to site by tugs. While this did notcause any problems in the relatively short journey that had to be made fromthe River Tyne to site, it would have implications for larger offshore sites.Towing barges to a site further offshore would have an impact on the time thatit would take to travel to site from port. Once on the site the tugs would alsobe required to help position the barges. Self-propelled barges would take lesstime to move to and from site and then once on site would be able tomanoeuvre into position without the assistance of tugs.
If this means specialist vessels have to be commissioned then the case isobvious. The installations of offshore wind turbines are so dependent on the
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sea state and can be held up with severe delays even in supposedly “good”weather months. Each delay in the installation programme is lost generatingtime and an increase to the cost of the project. Obviously installing a largerwind farm with an increased number of turbines could justify the capitalexpenditure on more specialist vessels.
7.2 Weather
Installation would be planned for “good” weather months, however not a greatdeal can be done to prevent delays due to weather. A flexible working plancould be implemented to enable parts of the project to be carried outsimultaneously. If there was a delay on one part of the project, work couldstill be progressing on another thus avoiding delay to the overall plan.
7.3 Site
When a site has been selected for an offshore wind farm full information isneeded on the seabed conditions, initially for the design of the foundations.For instance if the intention is to drive pile foundations rather than drilling intorock then it is particularly important to know the seabed conditions as a certaindepth of sediment will be needed for pile driving. (Piles cannot be driven intovery hard rock).
Secondly seabed conditions are needed from the point of view of theinstallation equipment that would be used. When the barges jack-up they puttheir legs down on to the seabed, so the barge operators need to know theconditions to establish first of all if the barge can operate at that site andsecondly to plan their operations and procedures.
7.4 Electrical Protection
Although this was not an issue with the Blyth Offshore wind farm there willbe implications for larger offshore wind farms. The Electricity AssociationEngineering Recommendation for G.59 – “Recommendations for theConnection of Embedded Generating Plant to the Regional ElectricityCompanies’ Distribution Systems” is only valid for generation up to 5MW.For much larger wind farms the G.59 protection would not be used, a moresophisticated protection system would need to be in place. This would bedetermined from investigations and discussions with the Distribution NetworkOperators and also the National Grid Company.
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Appendix A – TURBINE LOCATIONS & CABLE ROUTE
(NOT AVAILABLE ELECTRONICALLY)
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APPENDIX B – responsibility flow diagram
Shell
Huub denRooijen
Powergen
Dave Farrier
Nuon
HenkKouwenhoven
AMEC BorderWind
David Still
BOWLPROJECTCOMPANY
SHAREHOLDERS
Huub den Rooijen
Norman Rogers Bill Grainger
PROJECTMANAGEMENT
AMEC Marine
Steve Thwaite
Global MarineSystems
Andy Shaw
Vestas
Preben Poulsen
MAINCONTRACTORS
AMEC Watson
Duncan Watt
Seacore
Phil Wilkinson
LIC
Carsten Brendstrup
Falmouth Divers
Steve Roue
SUBCONTRACTORS
l
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Appendix C – PROJECT DIARY
Date ProgressPre-2000 Consents and Licences were approved. Lease negotiations
took place with the Crown Estates. Contract discussions wereheld and the foundation design and integration studies wereperformed.
Feb 2000 The Joint Venture Agreement was completed betweenPowergen Renewables, Shell, Nuon and AMEC BorderWind. Press and media releases were made detailing theproject and its partners.
Mar/May2000 The main contracts were placed with Vestas, AMEC, Seacoreand Global Marine Systems. At the same time the projectoffice was set up at South Harbour, Blyth.
Jun 2000 AMEC’s jack-up barge Wijslift-6 was fitted with the Seacoredrilling rig and other modifications that had to be made.
19 Jul 2000 The Vestas turbines were delivered to the AMEC storage yardat Howdon on the River Tyne.
25 Jul 2000 The steel monopile foundations were fitted with the J-tubes,access ladders and fenders to protect the ladders. The finaldetails were also being put to the access platforms.
8 Aug 2000 Cable trench on the beach (from shore to east pier) wascompleted.
9 Aug 2000 The monopile foundations were loaded on to the AMEC Atlasbarge ready for transportation to site.
14 Aug 00 The Wijslift-6 was in place at the offshore site and had begunjacking up to height for the initial drilling operations.
16 Aug 00 AMEC and Seacore completed installation and testing of themulti-stage drill bit.
17 Aug 00 Drilling of the first borehole (northern turbine) commenced.23 Aug 00 The first monopile was installed and grouted.25 Aug 00 Directional drilling down through the pier has been
completed and the ducting installed.8 Sep 00 Installation of the second monopile foundation was
completed. Preparations were underway to enable the firstwind turbine lifts to commence.
13 Sep 00 The first access platform was lifted into place and secured.Tower lifts will start when the weather conditions areappropriate.
17 Sep 00 The southern turbine tower has now been installed. This wasa two stage process, lower tower section first and the uppertower section.
19 Sep 00 The southern nacelle was installed today.25 Sep 00 Preparations were started for loading and transportation of the
first rotor. This is totally dependant on weather and swellconditions.
26 Sep 00 Work was completed by the divers removing silt from theriver bed at the quayside to assist with the installation of the
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cable ducts.27 Sep 00 Ducting installed at the quayside.30 Sep 00 The first rotor was installed on the southern turbine .3 Oct 00 The Wijslift moved station to the north turbine location and is
jacking up to the required level for platform and towerinstallation.
5 Oct 00 The switchgear, access platform and lower tower section havebeen installed at the north turbine location. The Wijslift thenhad to jack up to the higher level required for upper tower andnacelle installation.
6 Oct 00 The upper tower section and the nacelle were installed today.9 Oct 00 The second rotor has been installed. The activities that
remain to complete the wind farm are the installation of thecable to shore, onshore electrical works and turbinecommissioning.
9 Oct 00 The cable was laid from the southern turbine to the pier.12 Oct 00 The cable was pulled up through the directionally drilled hole
in the pier to the draw pit (manhole) on top of the pier.19 Oct 00 Dredging commenced across the River Blyth. Yellow
markers have been used on both sides of the river to indicatethe position of the cable ducts.
25 Oct 00 Dredging operations finished across the river and the profileof the trench was approved by Blyth Harbour.
28 Oct 00 Ducting installed across the river.29 Oct 00 The cable was installed from the pier to the quayside.1 Nov 00 Cable termination work was started in the north turbine.2 Nov 00 The cable trench across the river was back filled.3 Nov 00 Work started on cable installation from the quayside to the
onshore switchroom.4 Nov 00 Trench across river backfilled and completely finished.5 Nov 00 Cable termination work complete offshore.6 Nov 00 Cable installed into sub station.6 Nov 00 Cable termination completed onshore.8 Nov 00 Onshore cable trench backfilled and tarmac complete.10 Nov 00 Grid Connection11 Nov 00 Wind farm energised, circuit breaker settings checked.17 Nov 00 G59 Protection relay tests complete.20 Nov 00 Fibre optic terminations commenced.23 Nov 00 Fibre optic terminations complete.4 Dec 00 Turbine commissioning complete.
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Appendix D – WIJSLIFT 6 & SEACORE DRILLING RIG
Drawing reproduced by kind permission of Seacore.
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Appendix E – LIFTING OF THE MONOPILE
Drawing reproduced by kind permission of Seacore.
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Appendix F – CROSS SECTION OF CABLE
Conductor
ConductorConductor
Fibre Optic Cores
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Appendix G – 2.0MW BLYTH OFFSHORE WIND TURBINE
Α Λορρψ
BLADE TOP
NACELLE
ACCESS PLATFORM
SEABED (MUDLINE)
BOTTOM OF PILE
LOWEST ASTRONOMICAL TIDE
HIGHEST EVER RECORDED TIDE
NORTH SEA
ROCK
95m
62m
5.8m
15m
LORRY DRAWN TO SAME SCALEAS TURBINE