17292
Transcript of 17292
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THOMAS BOEHME, DNV KEMA
Managing Subsea Power Cable Risks
1315 May 2013, Bremen, Germany
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Managing Subsea Power Cable Risks
IQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
Content
ExperienceAction required
RisksAssessment and management
DesignConsiderations
Conclusions2
Export cable installation Picture source: DNV
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Managing Subsea Power Cable Risks
IQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
Part I
Experience to Date
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Managing Subsea Power Cable Risks
IQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
Experience
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7,000 kmMore than 7,000 km of HV ( 60 kV)cables are in service (onshore,offshore), many more system-kilometres at 33 kV and below.
80% claimsMany offshore wind farms haveexperienced problems with subseapower cables. Claim amounts*related to cables top the list.
120 yearsPower cables have been around fora long time. Designs have evolved,new materials are being used.Challenges offshore remain.
Data source: CIGR (2009);* Codan data, 2002-2011, claim cost
BA
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Managing Subsea Power Cable Risks
IQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
Experience: Offshore Wind
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Data source: DNV research(Shown: Reported in public domain)
20112005 2006 2007 2008 2009 20102004200320022001
Blyth
Delays
Inter-arraycables
Problem
Damage
Exportcables
Problem
Damage
Middelgrunden3 damages
Horns Rev ICable damage
North HoylePlanning deficiencies
UtgrundenCable replacement
UtgrundenCable replacement
Q7Vessel substitution
Robin RiggBarge evacuation
BarrowRemedial burial
Burbo BankCable damage
Burbo BankCable damage
ThanetRemedial work
Arklow BankAnchor damage
BarrowInstallation problems
BlythCable damage
Scroby SandsCable replacement
ThanetKink discovered
Walney IRegulator fine
Greater GabbardContractor bankruptcy
LincsRoute problems
Bard Offshore I
Diver fatality
2012
London ArrayCable damage
GalloperRoute issues
BarrowStanding loops
Alpha VentusCable damage
Gwynt y MrCable damage
Lynn & Inner DowsingCable repair
TeessideInstallation delays
WalneyOutage of string
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Managing Subsea Power Cable Risks
IQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
Offshore Wind Investigation
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Strong focus on price , not enough on risk
New staff Lack of knowledge transfer
Industry best practiceyet to be developed
Incidentsin virtually every wind farm
Most often during construction (95%*)
Sometimes during operation (5%*)
Data source: DNV stakeholder consultation* Codan data, 2002-2011, claim cost
Failure stat ist icsnot yet available
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Managing Subsea Power Cable Risks
IQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
Response: CableRisk Joint Industry Project
15 Participants Objective
- Develop a guidelinefor subseapower cablesin renewable energyapplications which- covers the cable lifecycle
- provides technical guidance
- improves communication betweenstakeholders
- helps managing the risks
Application
- Inter-array cables
- Export cables
- (Interconnectors)
Timeline
- Project: Aug 2012Jun 2013
- Industry review: May 2013
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INCH CAPE
Project responsible:
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Managing Subsea Power Cable Risks
IQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
Part II
Adopting a
Risk-Based View
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Managing Subsea Power Cable Risks
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Risk Basis
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Wind turbine
Substation
Subsea
export
cable
to shore
Subseainter-array
cable 19
1
1217
13
14
7
8
9
10
2
3
4
5
206
1116
15
18
Damage
What targetsexistdescribing good
(or good enough)
cable connections?
Target MTTR (days)?
Annual target
failure rate (%)?
Different targets for
- Construction phase?- Operations phase?
Different targets for
- Whole cable system?- Single cable?- Cable section?
Acceptable level of
injuries / fatalities?Environmental
impact?
NPV ()?
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Managing Subsea Power Cable Risks
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Hazards, Threats Risk
Hazard= Something that can cause harm (to people, environment, project)
Event= Hazard realisation
Risk = Event severity event probability
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Hazard realisation,event, incident ConsequencesCauses
Escalation
Prevent barriers
(facilities, processes, people)
Detect / control / mitigate /
recover barriers
Immediatecause
Rootcause
(consequence) (likelihood)
H&SEQ
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Acceptable
Intolerable
Tolerable
Lower Higher
Severity (log scale)
Lower
High
er
Pro
bability(logscale)
Risk Assessment Qualitativeassessment
simple, quick, provides an overview
subjective, needs scrapping (Chapman & Ward)
Quantitativeassessment
relatively objective, scientific backing
requires effort, more suitable for focus areas
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Sources: ISO 31000, ISO 31010, Chapman & Ward(2011), Kristiansen (2005)
Mitigation
H&S (or) E (or) Q
Cumul.probability(%)
100
50
0Lower Higher
Impact (, days)
Scenario A
Scenario B
P
robability(logscale)
Lower Higher
Severity (log scale)
Lower
Higher
Scenario A
Scenario B
H&S, E
Q
H&S, E, Q
Risk identificationanalysisevaluationtreatment (ISO 31000)
Management: PlanDoCheckAct
Risk management to be integrated intoproject management
H
Pro
bability
Severity
Acceptable
Intolerable
TolerableM
L
L M H
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Managing Subsea Power Cable Risks
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RisksHealth & Safety
Generally considered to be
relatively lowin cabling Mitigation (reduction) to as low
as reasonably practicable
(ALARP)
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Lower Higher
Severity
Lo
wer
Higher
Probab
ility
Diving fatality (2010)Bard Offshore I, Germany
A diver ... was diving at approximately 41
metres, and his air supply was cut off due
to an unintended squeezing of his
umbilical... The task was to removebottom material from the seabed [in front
of J-tubes]. A dredger pipe was being
positioned on the seabed, ... a job whose
execution deviated from the method
statementin which it is described it
should be done by ROV.
Diving
activities
All data: Illustrative only
Access &
transfer tooffshore units
HV test work
Work on cable
laying vessel
Confined
space work
(TP, MP)
Sources: Maersk (2011)
Working at
height
Escalation during
emergency response
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Managing Subsea Power Cable Risks
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RisksEnvironment
Risks require site-specific
assessment Mitigation (reduction), e.g. to as
low as reasonably practicable
(ALARP)
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Lower Higher
Severity
Lo
wer
High
er
Probab
ility
Seabed,
mudflats
disturbance
All data: Illustrative only
Disturbance
of fauna
Magnetic
fields
Construction
noise
Thermal
impact (?)(esp. Germany)
Sources: Centrica (2011, 2012), Bridgewatch (2011)
Construction delays (2011-2012)Lincs, United Kingdom
CREL ... tried to install two cable ducts
under the salt marsh and sea defences last
summer [2010], but this was not
successful. As the saltmarsh is of highconservation value, a new solution was
needed.
Nessie is now [2012] laying the 2ndcable
across the intertidal area, incorporating
knowledge ... gained from laying the 1st
cable in 2011.
Introduction of
new materials
(e.g. rocks)
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Managing Subsea Power Cable Risks
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RisksProject (Quality, Cost, Time)
Currently considered to be very
highin cabling Optimisationto a desirable and
appropriate level (threat vs.opportunity)
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Lower Higher
Severity
Lower
High
er
Probab
ility
Anchor
impact
All data: Illustrative only
Unexpected soil
conditions
Free spans
Sand waves
Fishing gear
impact
Sources: Thanet Offshore Limited (2005),reNews (2011), Windpower Offshore (2012)
Export cable repair (2012)Thanet, United Kingdom
A section of the export link in the inter-
tidal area of Pegwell Bay [has to be
replaced] ... the radius of the loop is
currently more acute (1.35 m) than therecommended 3.3 m.
The problem was resolved on 13 April
[2012]. The total cost to Vattenfall was
about 5.6m.
Weather
delays
Poor WTG
interface
design
Unsuitable
burial tool
Installation
delays Cable fault
Natural
catastrophe
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Managing Subsea Power Cable Risks
IQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
Part III
From Good Design
to Successful
Projects
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Managing Subsea Power Cable Risks
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Scope of GuidelineDraft
General
- Introduction, references, definitions,abbreviations
Design philosophy
- HSEQ, risk basis, assessment andmanagement
- System design principles
- Stakeholder interfacemanagement
Concept development and design- Field layout
- Regulatory requirements
- Site surveys
- Cable route engineering and burialassessment
- Marine conditions
- Seabed properties, sand waves,
- Infrastructure, navigation, living environment
- Cable specificationfor
- Site conditions
- Offshore construction, O&M
- Cableoffshore structure interface design
Manufacturing & testing
Installation and commissioning
- Marine operations planning (vessels,anchoring, positioning, human factors)
- Cable
- Route preparation
- Pull-in at offshore structure
- Laying and protection
- Landfall
-
Jointing, termination, testing- As-built survey
Operation and maintenance
- Remote monitoring
- Surveys, remedial work
- Fault detection, repair planning andexecution
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Orange: Focus area
Overall status: 90% completion
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Managing Subsea Power Cable Risks
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Cable ProjectsAppreciating Complexity
Quality checks
All relevant stakeholders consulted?
Started early with the planning and design?
Optimised and planned with contingencies?
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Electrical Thermal
Mechanical
Certifier, MWS
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Managing Subsea Power Cable Risks
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HV AC cableOffshore substationWind turbine generator Onshore substationMV AC cable
Electrical Considerations
Quality checks
Reliability targets set?
Failure rates applicable?
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3 x 1 x 240 mm2Cu33 (36) kV, 880 m
3 x 1 x 630 mm2Cu150 kV, 20,500 m
3 x 1 x 800 mm2Cu150 kV, 1,350 m
Ampacity
estimation
Topology
selection
Cablechoice
Reliability
check
Basic
power flow
LayoutMW, kV
R,XC
p.u., Mvar
Length
Choiceof mm2
Failure rate
NPV ()
Data sheets
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Managing Subsea Power Cable RisksIQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
HV AC cableOffshore substationWind turbine generator Onshore substationMV AC cable
Thermal Considerations
Quality checks
Site data available?
Hotspots ok?- J-tubes
- Soils with low conductivity
- Landfall
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th
Survey
Cable route
desktop study
Burialassessment
Cooling
verification
Constraints
Depth
Proposed corridor
Electricallosses
Back toelectrical study?
Siteparameters
, th
y
y
Losses
Example: 3 x 1 x 240 mm2Cu, 33 (36) kV
- Cable A: 467 A (< 20
C, < 1.0 K m / W)
- Cable B: 590 A (< 10
C, < 0.7 K m / W)
Pel
s
w
Data
Hazards
s
w
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Managing Subsea Power Cable RisksIQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
HV AC cableOffshore substationWind turbine generator Onshore substationMV AC cable
Mechanical Considerations
Quality checks
Installation weather dependent?
Optimised for smooth installation?
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Foundation
designConstruction
engineering
Warranty surveyor
verification
Trials
Cable properties
Methodstatements
Insurancecover?
Back toelectrical / thermal
study?
Site, vessel data
Radius,tension,
frictionFpull Movement
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Managing Subsea Power Cable RisksIQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
Example from Guideline: J-tubes
Main text: When designing J-tubes, the
following shall be considered:- adequate tube sizing (pull-in forces, cooling
of cable)
- avoidance of multiple bends
- smoothness of inner surface
- ...
Guidance note:- The inner diameter of the J-tube should not
be less than 2.5 cable outer diameter D tofacilitate cable cooling and avoid excessivepull-in forces.
-
The bending radius of the J-tube, measuredat the centre of the J-tube, should not be lessthan 20 cable outer diameter D, or larger, ifspecified by the cable manufacturer in orderto facilitate cable installation.
- ...
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Draft
Subject to project + industry review
Angle to seabed
Straight length
Flangefor cover
Distance toseabed
Bellmouth
Smoothtransition
Seabed
Bending radius
Inner diameter
Distance between tubes
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Managing Subsea Power Cable RisksIQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
Conclusions
Subsea power cabling is
- multi-disciplinary
- has frequently been underestimated
Cable risks require assessment over whole life cycle
Industry guidance is being developed22
Array cable pull-in Picture source: DNV
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Managing Subsea Power Cable RisksIQPC Offshore Cabling, 13 - 15 May 2013, Bremen, Germany
www.dnv.com
Joint Industry Project: [email protected]