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 SCFF cables largely superseded by extruded dielectric cables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