hv submarine cable systems design, testing and · pdf filedevelopment of submarine cables ......
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HV Submarine Cable Systems
Design, Testing and Installation
Robert Donaghy
Senior Consultant Engineer, ESB International
CIGRE Ireland Technical Seminar
6th October 2010
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Presentation Overview
• Applications
• Design
• Testing
• Installation
• Examples
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Submarine Cable Applications
• Interconnections
between grid systems
• Island connections
• Off-shore wind and wave
power connections
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Development of Submarine Cables
• 60-70s MV 3-core XLPE & EPR
• 1980s Large s/c core fluid filled up to 400kV
• 1990s 3-core dry type XLPE designs up to 145kV
• 2000- Long length XLPE 3-core & single core up
to 400kV
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Submarine Power Cable Types
Rated Voltage
Uo
33 kV ac 150 kV ac 420 kV ac 320 kV dc 450 kV dc
Insulation XLPE, EPR XLPE Oil/paper or
XLPE
Extruded Mass
Impregnated
Typical
application
Supply of small
islands,
connection of
offshore WTG
Supply to large
islands, offshore
platform export
cables
Crossings of
rivers, straits with
large
transmission
capacity
Long distance
connections of
offshore
platforms or wind
parks
Interconnection
of power grids
over long
distances
Max. length 20-30 km 70-150 km <50 km >500 km >500 km
Typical rating 30 MW 180 MW 700MW / 3
cables
1000 MW / cable
pair
600 MW / cable
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HV Cable Construction
Conductor
Sheath
Fibre Optic Cores
Armour
Outer Serving
Insulation
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Single Core Three Core
Pros
Lighter weight
Smaller Diameter
Longer lengths
Possibly fewer factory & field joints
Higher current rating
Improved security, can add a 4th cable
Voltage rating up to 400 kV and greater
Reduced repair costs and spares
Cons
Higher magnetic field
Greater installation costs
Individual seabed trenching increases costs
Protection costs increased
Sheath current must be considered
Pros
Reduced magnetic field
Lower sheath circulating currents and voltages
Lower installation costs
One trench on seabed
Lower protection costs
Includes optional Fibre Optic Cable
Cons
Lower current rating
Heavier
Large diameter
Security of cable system decreased
All three phases have to be repaired after a fault
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Electrical Design
• Voltage level (U0/U)
• Rated transmitted power (kVA)
• Short circuit current (kA) & duration (s)
• Load factor
• Maximum losses allowed
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Transmission Capacity Limits
0 MW
200 MW
400 MW
600 MW
800 MW
1000 MW
1200 MW
0 km 50 km 100 km 150 km 200 km 250 km 300 km 350 km 400 km
Un=400 kV
Un=132 kV
Un=150 kV
Un=230 kV
Cable
Length
Power*
* With compensation, based on 3-core 1,000mm² conductor, 400kV is 1-core 1,200mm² (ref. Nexans)
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Key Design Data
• Ambient temperature (seabed & land)
• Burial depth
• Particular burial/protection requirement at shore
approach (deeper burial, directional drill pipe…)
• Axial spacing of cables
• Thermal resistivity of seabed & land
• Length of submarine cable
• Water depths
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Connections to Floating Platforms
• Application specific
• Mechanical performance: movements and vibrations
• Hang-off arrangements on platform
• Corrosion protection and grounding conditions
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Route Survey
• Hydrographic & geophysical survey
• Sea bed bathymetry
• Tide data Level, met ocean data
• Locate existing cables & obstacles
• Multi-beam echo sounder
• Side scan sonar
• Sub-bottom profiling
• Core Sampling
Profile along cable route
• Water depth profile
• Corridor width
• Risk of damage to cables
• Burial depth/protection requirement
• Shore landing point selection
• Environmental assessment
• Consents, Foreshore Licence
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Sea Bed 3D Bathymetric Profile
Proposed Cable
Existing Cable
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Shore Landing
• Near shore civil works
• Directional drill, pulling through pipes
• Mechanical protection of cables
• Space for Sea/land transition joint
• Parallel routing of cables
• Environmental considerations
– Sand dune movements
– Erosion concern
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• Factory Joints
• Repair Joints
• Terminations
• Transition Joints
Accessories
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Testing
• Prequalification / Development Tests
• Type Tests
• Routine Tests
• Sample Tests
• After-Installation Tests
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CIGRE WG B1-27
• Test recommendations for long AC extruded submarine cables 150 - 500 kV (now also to cover 36 - 150kV)
• Addresses particular requirements of submarine cable systems:– Water tightness of conductor and under metallic sheath
– Armouring
– Mechanical forces during installation of cable and joints
– Water tightness of rigid joints
– Delivery lengths and weights
– Routine tests of cable and joints – challenges in testing long lengths
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CIGRE WG B1-27
Recommendations
• More stringent approach Partial Discharge measurement in factory joints
• Extended frequency range for ac tests: 10 – 500 Hz
• External water pressure test of rigid sea & repair joints
• Scheme for mechanical tests for repair joints
• Tests for visual inspection of submarine cables
• Range of approval for type tests modified: factory joints, mechanical testing etc
• Prequalification and Extended Qualification
• Factory joints still to be qualified
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Cable Laying Vessels
In the old
days…
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Cable Laying Vessels
Now…
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Cable Laying
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Cable Laying Vessels
Shallow draft barges
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Protection
Dropped objects
Anchoring
Fishing
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1/4
SoftHard
m
Penetration of smaller anchors &
fishing gear vs. soil hardness
1/2
1
3/4
1 T anchor
500 kg anchor
400 kg anchor
200 kg anchor
Otter trawl
Beam trawl
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2.5 m
Cable buried in hard to soft
sediments to 0.5 – 3.0m
Embedment by water jetting
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ProtectionEmbedment
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Cork Harbour Project
• One of the first 220kV XLPE submarine
projects in the world
• Two circuits: Single core 1 x 1,600mm²
copper, 570MVA rating
– 3.5km length: Aghada-Raffeen 220kV
– 4.5km length: Glanagow-Raffeen 220kV
• Continuous manufacturing lengths up to 4.5km
• Shallow water: 10 metres (1st crossing), 30
metres (2nd crossing)
• Crossing main shipping channel of major port
• Submarine cable embedment by water jetting
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4.6km
3.3km
Legend
220kV Submarine Cable
220kV Land Cable
6km
1.4km
3km
0.5km
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Picture Area
Cork Harbour 220kV: Feb 2010
Cable Laying Vessel
Cable shore landing
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SEAI Wave Energy Test Site
2 x 15km 20kV subsea
cables
2 x 7km 20kV subsea
cables
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Ireland – Wales East West
Interconnector
186km Marine Route
45km Land Cable in Ireland
30km in Wales
Converter Stations at Woodland & Deeside
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Thank you
for your attention