cable installation & trenching challenges in offshore wind farms

NORTH OF ENGLAND EVENING MEETING
March 18th 2015
http://www.sut.org/
CABLE INSTALLATION & TRENCHING CHALLENGES IN OFFSHORE WIND FARMS
Patrick Smyth
1
AGENDA
• Offshore Wind in UK
• Offshore Wind Farm Layout
• Offshore Substations
• Wind Turbine Generators
• OWF Cables
• Cable Protection Systems
• Installation and Trenching Challenges
• Crew Transfer
• Summary & Conclusions
P.2
OFFSHORE WIND IN UK
Offshore Wind in UK:
• The UK is the world leader in Offshore Wind
• The 1st Offshore Wind Farm (OWF) in the UK was in Blyth Harbour (2000)
• OWF developed with a series of licensing ‘Rounds’ co‐ordinated by the Crown Estate
• Round 1 (2001) ‐ 18 sites in England and Wales
• Round 2 (2003) ‐ further offshore and in deeper waters
• Round 3 (2010) ‐ nine zones across the UK
P.3
OFFSHORE WIND IN UK
Source: The Crown Estate
P.4
OWF FIELD LAYOUT
Typical field layout:
• Wind Turbine Generators (WTG)
• Inter‐Array Cables
• Offshore Substation(s)
• Export Cables
Source: RWE Innogy
P.5
OFFSHORE SUBSTATION
Offshore Substation (OSS) / Offshore Substation Platform (OSP)
Source: 4C Offshore
P.6
OSP PULL‐IN ‐ CHALLENGES
● Upper decks in place
● Headroom on hang‐off deck
● Deck loading
● Landing area
● Space availability
● Pull‐in Winch Location
● J‐tube #/Location/Configuration
● Cable Routing
● Cable over‐pull lengths ● Termination Location
P.7
WIND TURBINE GENERATOR (WTG) / MP
Wind Turbine Generator (WTG):
1. Blades
2. Nacelle
3. Tower
4. Transition Piece (TP) + Monopile (MP)
5. Inter‐array Cable +
Cable Protection System (CPS)
Source: GLID
P.8
WIND TURBINE GENERATOR STRUCTURES
• Jacket
• Tripod
Source: Areva
Source: BARD Group
Source: Power Technology
P.9
FLOATING WIND TURBINE GENERATOR
• Tripod
• Jacket
• Floating
Source: Wind Float Pacific
P.10
WTG PULL‐IN ‐ CHALLENGES
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•
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•
•
•
•
•
•
•
•
J‐tube/I‐tube/Aperture
Height above seabed / Vertical pull‐in angle
Scour / Scour Protection
WTG towers/nacelles in place
TP covers in place
Marine growth around bell mouth or apertures
WTG Landing / Deck Loading
Pull‐in Points
Over‐pull Length
Dragging cable on seabed
Protection of Cable MBR
P.11
SECOND END PULL‐IN
Typical 2nd end cable pull‐in options:
• Pull‐in cable bight along seabed
• Use Sliding Quadrant from vessel
• Lay cable on seabed and engage with quadrant subsea
P.12
OWF CABLES
OWF Cables:
• Export Cables
• Inter‐Link Cables
• Inter‐Array Cables
NE England Cable/Umbilicala Mfg
• JDR Cables
• Technip
P.13
Other Mfg:
• ABB
• Nexans
• NKT
• NSW
• Prysmian/Draka
OWF CABLES
Key Parameters (for installation)
Typical Value
Minimum Bend Radii (MBR)
< 5m
Specific Gravity
> 1.7 Weight / metre (Air / Water)
c. 100 kg/m / c. 40 kg/m
Max. Pull‐in Force
> 3 tonne
P.14
CABLE PROTECTION SYSTEMS (CPS)
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•
•
•
•
Bend Stiffeners
Bend Restrictors/Limiters
Seals
Centralisers
Cable Protection Ducting
NE England CPS Mfg
• Pipeline Engineering
Other Mfg:
• Balmoral
• BMP
• Pipex px
• Trelleborg
• Subsea Energy Solutions
• Tekmar Energy
P.15
•
•
•
•
Blue Ocean
CNPL
Seaproof
Vos Prodect
CABLE PROTECTION
Other Methods
• Concrete Mattress
• Rock Dump
• Rock Filled Filter Units
Source: Windpower Offshore
Source: Jan De Nul
P.16
Source: Marske Site Services
CPS ‐ CHALLENGES
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Cost
Pre‐installed Onshore / Installed offshore
Installation time
Reliability
Sealing
Corrosion
Foundation Interface
Handling & Storage
P.17
EXAMPLE OF CABLE LAY & BURIAL OPERATIONS
• Free Lay
• Pre Cut Trench
• Simultaneous Lay & Burial
• Post Burial
P.18
OWF CABLE BURIAL
• Protection against: • Environmental conditions
• Trawl damage
• Anchor damage
• Dropped objects
• Reduction of Freespan
• Cable Design
P.19
Source: Lloyds
INSTALLATION & BURIAL CHALLENGES
Parameter
Typical Value
Working Environment
Water depth (below LAT)
5m to 35m
Tidal range 1m to 10m
Current
up to 4kts
Subsea visibility
zero to 10m
Environmental (wind / waves)
up to 50kts / Hsig up to ~6m Seabed
Soil type: clays (cohesive)
3kPa ‐ 1000kPa
Soil type: sands (granular)
Loose, coarse to dense, fine
Seabed bathymetry
up to 30° (usually on sand waves)
Boulders; other cables / wires / debris; wrecks; UXO 0.5m to 3.0m / 0m to 2.5m
Obstacles
Target Depth of Lowering / Depth of Cover
Infrastructure & Hardware
Foundation configuration
WTG in place (majority)
Scour protection
Cable Protection System (CPS)
Configuration
Sealed or unsealed
Outside Diameter
ø500mm
Centraliser Latch Tension
1Te to 4Te
Minimum bend radius
2.5m
Inter Array Cables (IAC's)
Cable Design
P.20
CREW TRANSFER ‐ CHALLENGES
CTV Transfer
Motion Compensated Systems:
• Houlder TAS (Turbine Access System)
• OSBIT Power MaXccess Access Systems
Source: Houlder Ltd
Source: Siemens
• Ampelmann
• Uptime
Source: Ampelmann
P.21
Source: Uptime
SUMMARY & CONCLUSIONS
Summary:
● Significant challenges associated with the OWF cable installation and burial
● Reduce offshore operations and worktime
● Reduce weather dependent operations
● Increase limits for operations
● Identify and share best practices ● Involve all parties at the earliest possible stage
● Adhere to industry guidelines
● Examine innovative solutions
● NE England Companies are work leaders P.22
THANK YOU
NORTH OF ENGLAND EVENING MEETING
March 18th 2015
http://www.sut.org/
INSTALLATION CHALLENGES IN OFFSHORE RENEWABLES
Patrick Smyth
23