06 HVDC Cable Line Technologies - ROBERT DONAGHY (ESB International)

HVDC Grids Workshop Cable Line Technologies 11th December 2012 Bizkaia Aretoa, Bilbao, Spain

Robert Donaghy Senior Consultant Engineer, ESB International

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 SCFF cables largely superseded by extruded dielectric cables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.

DC Cables –Selection Guideline 3500 MW

> 2400

600

Mass Impregnated (MI) Traditional or PPL insulated D.C. Cable Systems

SYSTEM VOLTAGE [kV]

525 A.C. / D.C. Fluid Filled Cable Systems

400

1200

1000

320

200

A.C. Extruded of Fluid Filled Cable Systems Extruded D.C. Cable Systems (or Traditional MI)

100

600

400

50 10

1400

A.C. Extruded Insulation Cable Systems 40

60

80

100

120

140

No theoretical limit for D.C.

ROUTE LENGTH [km] A.C. one 3-phase system

D.C. one bipole

SYSTEM POWER [MW]

D.C. Fluid Filled Cable Systems

Accessories • Factory Joints • Repair Joints • Field Joints (land & submarine) • Terminations - Outdoor • Sea – Land Transition Joints

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 Anchoring

Fishing

Dropped objects

Penetration of smaller anchors & fishing gear vs. soil hardness

m

1 T anchor 1

500 kg anchor 3/4 400 kg anchor 200 kg anchor 1/2 Otter trawl Beam trawl 1/4

Hard

Soft

Penetration of anchor vs. soil hardness

m 5

4

3

2

1

Hard

Soft

Embedment Cable buried in hard to soft sediments to 0.5 – 3.0m

2.5 m

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