subsea power connections that work

THOMAS BOEHME, DNV KEMA

Subsea Power Connections that Work

04 – 07 Feb 2013, Vienna, Austria

Boehme, T.: “Subsea Power Connections that Work”

EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria

Contents

1. Experience History Concerns

2. Design considerations Electrical Thermal Mechanical

3. Conclusions

2



Experience

3

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 have experienced problems with subsea power cables. Claim amounts related to cables top the list.

120 yearsPower cables have been around for a long time. Designs have evolved, new materials are being used. Challenges offshore remain.



Fishing44.4%

Anchors14.6%

Components 7.2%

Abrasion3.7%

Geological 2.6%

Other6.2%

Unknown 21.3%

Experience – “Other” Subsea Cables

Subsea interconnections ≥ 60 kV- 3,700 km AC, 3,400 km DC (2005)- ~ 50 damages in 1990-2005:

- 80% in water depths < 50 m- Many on unprotected cables,

e.g. through fishing and anchors

Subsea telecom cables- > 1,000,000 km in service

(fibre optic, 2009)- Frequent damages, but network

built with redundancies

4

Data sources: Cigré (2009), Carter et al. (2009)

11 1154

115

2

0

5

10

15

20

25

Internal External Other Unknown

Num

ber

of o

utag

es Cause of outage DC

AC

63

176

4

23

7

0

5

10

15

20

25

0-5 years 6-10 years 11-15 years 16-20 years > 20 years

Num

ber

of o

uta

ges Age at outageDC

AC



Experience – Offshore Wind Energy

5

Strong focus on price , not enough on risk

Lack of transfer of knowledge

“Industry best practice” yet to be developed

Incidents in virtually every wind farm

Most often during constructionSometimes during operation

€

Data source: DNV stakeholder consultation

Failure statistics not yet available



“CableRisk” Joint Industry Project Initiative

15 Participants

Objective- Develop a guideline for subsea

power cables in renewable energy applications which- covers the cable lifecycle- provides technical guidance- improves communication between

stakeholders - helps managing the risks

Timeline- Project: Aug 2012 – Jun 2013- Industry review: Spring 2013

6

INCH CAPE

Project responsible:



Cable Projects – Appreciating Complexity

Quality checks

All relevant stakeholders consulted?

Started early with the planning and design?

Optimised and planned with contingencies?

7

Electrical Thermal

Mechanical



HV AC cableOffshore substationWind turbine generator Onshore substationMV AC cable

Electrical

Quality checks

Reliability targets set?

Failure rates applicable?

8

3 x 1 x 240 mm2 Cu33 (36) kV, 880 m

3 x 1 x 630 mm2 Cu150 kV, 20,500 m

3 x 1 x 800 mm2 Cu150 kV, 1,350 m

Ampacityestimation

Topologyselection

Cablechoice

Reliabilitycheck

Basicpower flow

LayoutMW, kV

R, XC

p.u., Mvar

Length

Choiceof mm2

Failure rate

NPV (€)

Data sheets




Thermal

Quality checks

Site data available?

Hotspots ok?- J-tubes- Soils with low conductivity- Landfall

9

th

SurveyCable route

desktop study

Burialassessment

Coolingverification

Constraints

Depth

Proposed corridor

Electricallosses

Back toelectrical study?

Siteparameters

, th

y

y

Losses

Example: 3 x 1 x 240 mm2 Cu, 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




Mechanical

Quality checks

Installation weather dependent?

Optimised for smooth installation?

10

Foundationdesign

Constructionengineering

Warranty surveyorverification

Trials

Cable properties

Methodstatements

Insurancecover?

Back toelectrical / thermal

study?

Site, vessel data

Radius,tension,frictionFpull Movement



Conclusions

Subsea power cabling- is multi-disciplinary- has frequently been underestimated

Cable risks require assessment over whole life cycle

Industry guidance is being developed

11



www.dnv.com

Joint Industry Project: [email protected]

subsea power connections that work

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