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THOMAS BOEHME, DNV KEMA

Managing Subsea Power Cable Risks

1315 May 2013, Bremen, Germany

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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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Part I

Experience to Date

3

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Experience

4

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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Experience: Offshore Wind

5

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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Offshore Wind Investigation

6

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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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

7

INCH CAPE

Project responsible:

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Part II

Adopting a

Risk-Based View

8

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Risk Basis

9

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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Hazards, Threats Risk

Hazard= Something that can cause harm (to people, environment, project)

Event= Hazard realisation

Risk = Event severity event probability

10

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

11

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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RisksHealth & Safety

Generally considered to be

relatively lowin cabling Mitigation (reduction) to as low

as reasonably practicable

(ALARP)

12

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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RisksEnvironment

Risks require site-specific

assessment Mitigation (reduction), e.g. to as

low as reasonably practicable

(ALARP)

13

Lower Higher

Severity

Lo

wer

High

er

Probab

ility

Seabed,

mudflats

disturbance


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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RisksProject (Quality, Cost, Time)

Currently considered to be very

highin cabling Optimisationto a desirable and

appropriate level (threat vs.opportunity)

14

Lower Higher

Severity

Lower

High

er

Probab

ility

Anchor

impact


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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Part III

From Good Design

to Successful

Projects

15

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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

16

Orange: Focus area

Overall status: 90% completion

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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?

17

Electrical Thermal

Mechanical

Certifier, MWS

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HV AC cableOffshore substationWind turbine generator Onshore substationMV AC cable

Electrical Considerations

Quality checks

Reliability targets set?

Failure rates applicable?

18

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


Thermal Considerations

Quality checks

Site data available?

Hotspots ok?- J-tubes

- Soils with low conductivity

- Landfall

19

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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Mechanical Considerations

Quality checks

Installation weather dependent?

Optimised for smooth installation?

20

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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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.

- ...

21

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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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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www.dnv.com

Joint Industry Project: [email protected]

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