Olympic Tunnel 400kV Cable Project Hackney Substation

To West Ham Substation

Experience

Prysmian has been responsible for the design, supply, installation and commissioning of over 450Km of Supertension cables in 44 tunnels worldwide. Of which 9 are in the UK.

In January 2006 Prysmian was awarded the contract to design, supply, install and commission the 400kV XLPE cables, accessories, support systems and monitoring systems for the West Ham – Hackney tunnel.

Project scope

• Full turnkey project to design, supply, install & commission two 400kV cable circuits.

• Tunnel length 6km

• Tunnel diameter 4.15 metres

• Circuit length 6.3km

• Install and commission both circuits by September 2008.

• Tunnel to be cleared of temporary services

Prysmian Supply scope

Cables: Single core, 2500mm2 copper conductor, XLPe Insulated, Aluminium Sheath, flame retardant oversheath. 48drums, 810m section length. Cable weight 36kg/m.

Accessories: 36 sectionalised 400kV joints, 6 un-sectionalised 400kV joints, 12-400kV outdoor terminations with composite insulators.

Monitoring: Continuous Partial Discharge monitoring for all joints and terminations. Continuous monitoring for sheath voltage limiters at each joint bay.

Prysmian Supply scope

Steelwork: 210 tonnes of steelwork designed, manufactured and installed to support the cable and accessories in the tunnel and above ground.

Substations: Design and construction of:

- Cast in-situ cable troughs from the tunnel shafts to the Outdoor terminations at Hackney & West Ham.

- Associated cable support structures and foundations.

- Cable trough forced air ventilation systems.

- DAR Cable Protection.

- Surge Arrestors.

Tunnel constraints

• 4.15 metre diameter tunnel with no level base for ease of access or use of vehicles – solution was to design and manufacture vehicles to run on monorail.

• Tunnel designed for 4 circuits with the first two circuits to be installed at the top level on either side of the tunnel.

• All installation and jointing works carried out at some two metres from tunnel invert necessitating special mobile platforms for all works and large scaffold structures (26 tonnes of scaffolding per joint bay) for jointing works.

Project successes

• Installed 48 drums of cable in 12 weeks.

• 4500 cable sags completed in 12 weeks.

• 42 cable joints and 6 outdoor sealing ends installed in 17 weeks.

• 210 tonnes of steelwork installed throughout the tunnel and shafts.

• 300 tonnes of scaffolding installed into and removed from the tunnels and shafts within the 6 month cable installation and jointing programme.

• Overall installation project completed in 30 weeks due to parallel working patterns.

System Design

Rating Requirements

• Summer 1660 MVA (2396 Amps)

• Spring / Autumn 1790 MVA (2584 Amps)

• Winter 1950 MVA (2815 Amps)

• An additional two circuits would be added at a later date and the above ratings will change

2

3

4

5

6

7

8

1

1. Central filler2. Milliken conductor3. Conductor screen4. XLPE Insulation5. Insulation screen6. Semi-conducting hygroscopic binder7. Aluminium sheath8. PE oversheath

400 kV XLPE Cable with 2500 mm² Copper Conductor

Main Cable Features

• Milliken conductor with low AC resistance.

•XLPE insulation

•Thick longitudinally welded aluminium sheath.

• Flame retardent oversheath.

•Cable is light and robust.

Skin effect

Proximity effect

Reducing AC resistance

• Milliken divides conductor into sectors• Improves current density in sector• Reduces skin effect• Widely spaced cables reduces proximity effect• Reduced AC resistance means improved rating

Ref No.

Title

DWG No. Date

Drawn by

Company

Customer

Verified by

Symbols

Issue No.

E\E\901\L

GW

VJB

1

Outdoor Termination Unsectionalised Joint

Sectionalised Joint

Cable: 2500mm2 Copper Conductor, 400kV XLPE Cable

Note:- all sectionalised joints will have SVL's fitted across the sectionalisinginsulation

Detail of cross bonding andSVL connections

SVL

SVL

SVL

West Ham S/SHackney S/S

West Ham - Hackney400 kV CircuitNational Grid

STS9221/D1 issue 3 11/04/06

1LNB-2072

LBM 7A

Single core 300 mm²bonding strands Single core 500 mm²

bonding strands

B B B B B B

B: LBM 3A

Schematic Arrangement of Circuit

• 2 x sections with sheaths single point bond• 2 x major sections with sheaths cross-bonded

Single Point Bonded Sheaths

• No circulating currents in the sheath – better rating.• Sectionalising insulators protected by SVL.• Earthing interconnector to carry the return fault current

Vr 00 Vb 1200 Vy -1200+ + = 0`

• Crossed bonded cables are installed in multiples of three.• Sheaths voltages balanced out over three-sections.• No circulating currents – No sheath losses – Higher ratings.• Joints sectionalising insulators protected by sheath voltage limiters (not shown)

Cross-Bonded Sheaths

Heat FlowThrough Ground

Heat Flow byTunnel Air Ventilation

HeatGenerated

byCables

TA (inlet)

TA (outlet)

Cable Rating Assessment

•Cables will generate losses• Majority of heat removed by air ventilation.• Rating assessed by Cigre methods

•Electra 143• Electra 144

Monitoring Systems

Types of Monitoring System

• Distributed Temperature Sensor (DTS)• Sheath Voltage Limiter (SVL)• Partial Discharge (Pd)

DTS Monitoring System

• The temperature sensor is an optical fibre cable.• The characteristics of the fibres will change with

temperature.• The temperature can be measured for the complete

route.• The hot-spots can be identified. • The cable / tunnel temperatures are measured

using DTS hardware locate at one substation. • The tunnel ventilation can be adjusted to suit.

DTS Fibre Attached to Cable

•Other fibres installed top and bottom of tunnel.

SVL Monitoring

SVL Monitoring

• Optical fibre and mirror wrapped around SVL.

• Reflected signal – SVL operational.

• Loss of signal – SVL failed

Optical signal

Reflection

SVL Monitoring display

HMI - All SVL’s Operational

HMI - SVL failed on System 1 J.B. 2/3

Partial Discharge Monitoring

• All accessories monitored for PD.• Used during commissioning and in service.• No power supply in tunnel.• PD measurements sent by fibre optic cable to

the outside of the tunnel.

PD Monitoring display

Cable Installation Jointing and Testing

Project successes

• Installed 48 drums of cable in 12 weeks.

• 4500 cable sags completed in 12 weeks.

• 42 cable joints and 6 outdoor sealing ends installed in 17 weeks.

• 210 tonnes of steelwork installed throughout the tunnel and shafts.

• 300 tonnes of scaffolding installed into and removed from the tunnels and shafts within the 6 month cable installation and jointing programme.

• Overall installation project completed in 30 weeks due to parallel working patterns.

Planned Cable Arrangement at Shaft 3

Cable Installation at Shaft 3- Hackney

Tunnel layout

Schematic cable & winch arrangement

Tunnel cross section

Trial cable delivery

Trial cable delivery - Hackney

Cable convoy - Stratford

Drum storage at shaft 2

Steelwork installed ready for rollers

Shaft 2 prior to scaffolding

Looking down shaft 2 scaffolding

Base of shaft 2 ready for cable

Monorail working platform

Cable installation at height

Cable installation at shaft 2

Scaffolding at top of shaft 2

Pipes at top of shaft 2

Pipes on scaffolding at top of shaft

Back tension winch at shaft 2

Cables installed at high level

Transposition by joint bays

Transposition by joint bays

Cable transposition

Transposition at joint bay

Sagging of cables

Sagging of cables

Training area for jointing

Training area for jointing

Training area for jointing

Joint bay platform

Joint bay

Completed joint

Completed joints

Completed joint bay

HV Test Arrangement

Termination Arrangement at Hackney