HVDC Grids Workshop
Cable Line Technologies
Robert Donaghy Senior Consultant Engineer, ESB International
11th December 2012
Bizkaia Aretoa, Bilbao, Spain
Overview
• Requirements of HVDC Cables • HVDC Cable Types • Testing • Route Selection & Survey • Installation • Reliability
Requirements of HVDC Submarine Cables
• Power transmission requirements • Long continuous lengths • Good abrasion and corrosion resistance • Mechanical strength to withstand all laying and
embedment stresses • Low environmental impact • High reliability with low fault probability.….but must
be capable of being repaired!
HVDC Cable Types
• 3 Main Types: –Mass Impregnated –Self Contained Fluid Filled –Extruded
Mass Impregnated DC Cable Conductor Insulation - lapped paper insulation impregnated with high viscosity dielectric fluid Metallic sheath Polymeric oversheath Armour (for submarine cables) Polypropylene yarn serving Long and proven service history Max conductor temp 55oC, but being developed to operate at higher temperatures
Self Contained Fluid Filled Cable
Conductor with central oil duct – fluid expands and contracts under load variations Insulation - lapped paper impregnated with a low viscosity dielectric fluid under pressure Metallic sheath - corrugated or smooth aluminium or lead reinforced with metal tapes Polymeric oversheath
Used mainly for short lengths. SCFF cables largely superseded by extruded dielectric cables
Mass Impregnated & Integrated Return Conductor
Extruded DC Cable Conductor Insulation – cross linked polyethylene (XLPE) Metallic sheath Extruded polymeric oversheath Armour (for submarine cables) Polypropylene yarn serving Historical problem of space charge accumulation. Now developed up to 320 kV. Limited service history up to now, but developments up to 500kV likely in future.
40 60 100 80 120 140
D.C. Fluid Filled Cable Systems
A.C. / D.C. Fluid Filled Cable Systems
A.C. Extruded of Fluid Filled Cable Systems
A.C. Extruded Insulation Cable Systems
Mass Impregnated (MI) Traditional or PPL insulated D.C. Cable Systems
Extruded D.C. Cable Systems (or Traditional MI)
ROUTE LENGTH [km]
SYST
EM P
OW
ER
[MW
]
SYST
EM V
OLT
AGE
[kV
]
1400
600
1200
1000
400
> 2400
No theoretical limit for D.C.
D.C. one bipole A.C. one 3-phase system
3500 MW
DC Cables –Selection Guideline
600
525
320
200
50
100
10
400
• Factory Joints
• Repair Joints
• Field Joints (land & submarine)
• Terminations - Outdoor
• Sea – Land Transition Joints
Accessories
Testing Range of Tests
– Prequalification / Development Tests – Type Tests – Routine Tests – Sample Tests – After-Installation Tests
CIGRE Test Recommendations
Non-Extruded Cables – CIGRE Electra 189 – Recommendations for Tests of Power
Transmission DC Cables for a rated Voltage of up to 800kV
Extruded Cables (XLPE) – CIGRE Brochure 496 - Recommendations for Testing DC Extruded
Cable Systems for Power Transmission at a Rated Voltage up to 500 kV
Cable Installation
• Survey & Route Selection • Cable Laying • Post – lay mechanical
protection
Survey & Route Selection • Hydrographic / geophysical survey • Sea bed bathymetry / water depth • Tidal data, met ocean data • Existing cables & obstacles • Corridor width • Burial depth/protection • Environmental assessment • Consents
• Survey tools
– Multi-beam echo sounder – Side scan sonar – Sub-bottom profiling – Core Sampling
Example of Route Profile
Shore Landing
• Near shore civil works • Directional drill, pulling through pipes • Mechanical protection of cables • Space for Sea/land transition joint • Environmental considerations
– Sand dune movements – Erosion concern
Cable Laying Vessels
In the old days…
Cable Laying Vessels
Cable Laying Vessels
Cable Laying
Protection
Dropped objects
Anchoring
Fishing
1/4
Soft Hard
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
Penetration of anchor vs. soil hardness
1
2
3
4
5
Soft Hard
m
2.5 m
Cable buried in hard to soft sediments to 0.5 – 3.0m
Embedment
Water Jetting Plough
Post – Lay Protection Embedment
Installation on Land
Reliability CIGRE Brochure 398: Third-Party Damage to Underground and Submarine Cables (2009) Underground cables: 70% of failures caused by mechanical work. 40% of all third-party damage due to insufficient information exchange between cable operators and construction companies. The probability of failure by external mechanical damage is > 10 times higher for direct-buried cable systems than for ducts or tunnels. Submarine cables: Due to small number of failures and limited data, no reliable conclusion on relation between installation method and failure probability. Average failure rate lower for submarine cables than for U/G cables. External damage most common reason for failures.
Eskerrik asko zure arretagatik
Gracias por su atención
Thank you for your attention
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