subsea power connections that work
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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
Boehme, T.: “Subsea Power Connections that Work”
EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria
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.
Boehme, T.: “Subsea Power Connections that Work”
EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria
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
Boehme, T.: “Subsea Power Connections that Work”
EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria
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
Boehme, T.: “Subsea Power Connections that Work”
EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria
“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:
Boehme, T.: “Subsea Power Connections that Work”
EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria
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
Boehme, T.: “Subsea Power Connections that Work”
EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria
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
Boehme, T.: “Subsea Power Connections that Work”
EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria
HV AC cableOffshore substationWind turbine generator Onshore substationMV AC cable
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
Boehme, T.: “Subsea Power Connections that Work”
EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria
HV AC cableOffshore substationWind turbine generator Onshore substationMV AC cable
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
Boehme, T.: “Subsea Power Connections that Work”
EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria
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
Boehme, T.: “Subsea Power Connections that Work”
EWEA 2013 Annual Event, 04 – 07 Feb 2013, Vienna, Austria
www.dnv.com
Joint Industry Project: CableRiskJIP@dnvkema.com
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