Walney Extension OFTO

Offshore GridOperationalGB660 MW220 kV173.6 km

Basic Information

Also known as:Walney Extension Transmission Assets, Diamond Transmission Partners Walney Extension, WOW03+04 Transmission Assets, Walney Extension OFTO TR5

Status:Operational

Capacity:660 MW

Transmission Model:Developer Build & Transfer

Owners:

Diamond Transmission Corporation Limited

HICL Infrastructure Company Limited

Chubu Electric Power Co., Inc.

Project Company:

Diamond Transmission Partners Walney Extension Limited

Type:offshore grid

Expected Life:20 years

Website:www.diamondtransmissionpartners.com

Description:

Walney Extension OFTO is the offshore transmission link that connects the 659 MW Walney Extension offshore wind farm (WOW03 + WOW04) in the Irish Sea to the onshore National Grid at Middleton (Heysham). The transmission system is an HVAC scheme comprising two 220 kV export circuits — one for each...

Supply Chain (0)

Project Timeline (0)

No lifecycle events recorded yet.

	Irish Sea	Irish Sea	Cumbria
Landfall	N/A	N/A	—
Grid Connection	—	—	Middleton 400 kV substation (NGET Middleton)

Financial

£446.6M€659.4M adj.€5.76k/MW-km

www.ofgem.gov.uk (Jun 2020)

CAPEX:£446.6M

Adjusted to 2025¹:€659.4M

Cost Intensity¹:€5.76k per MW-km

Estimate Date:Jun 2020

Source:www.ofgem.gov.uk

Notes:

Final assessed OFTO transfer value for the Walney Extension transmission assets per Ofgem (£446.6m). Industry and developer sources commonly round this to £447m; financial close/transfer announced June 2020.

¹ Cost inflated in local currency then converted to euros (where applicable).

Cable Specifications

WOW03 — Middleton export cable system

Heysham, Lancashire, United Kingdom

1 × 220 kV HVAC · aluminium 1200 mm² · XLPE (Cross-linked Polyethylene) · 330 MVA · 79.6 km

System:1 × 220 kV HVAC

Construction:aluminium · 1200 mm²

Insulation:XLPE (Cross-linked Polyethylene)

Power rating:330 MVA

Route length:79.6 km(75.7 subsea · 3.9 land)

Burial depth:

Project documentation does not specify a single uniform numeric burial target for the WOW03 export route in the provided excerpts. Sources state the export route comprises subsea and onshore sections...

Fibre optic:

The 220 kV export cables are described as having integral optical fibres and an adjacent fibre-optic cable (single-mode and multimode) is routed alongside the onshore 220 kV export cables. At...

WOW04 — Middleton export cable system

Heysham, Lancashire, United Kingdom

1 × 220 kV HVAC · aluminium 1200 mm² · XLPE (Cross-linked Polyethylene) · 330 MVA · 71 km

System:1 × 220 kV HVAC

Construction:aluminium · 1200 mm²

Insulation:XLPE (Cross-linked Polyethylene)

Power rating:330 MVA

Route length:71 km(67 subsea · 4 land)

Burial depth:

Export cables were installed buried where feasible along the route and transition to shore was completed using HDD at the landfall. The route crosses areas of sand/gravel and zones with...

Fibre optic:

The export cable systems include integral optical fibres. The project also places fibre-optic cable (single-mode and multi-mode) adjacent to each 220 kV onshore export cable; two of the fibres are...

WOW03–WOW04 subsea interlink

1 × 220 kV HVAC · aluminium 500 mm² · XLPE (Cross-linked Polyethylene) · 23 km

System:1 × 220 kV HVAC

Construction:aluminium · 500 mm²

Insulation:XLPE (Cross-linked Polyethylene)

Route length:23 km(23 subsea)

Burial depth:

Inter-platform subsea interlink is routed fully offshore (no landfalls). Sources describe the interlink as a subsea cable and the project-wide approach is to bury cables where practicable and protect/unburied sections...

Fibre optic:

Project documentation states the 220 kV export/interlink cables are 220 kV rated XLPE with integral optical fibres. The onshore export arrangements explicitly mention single-mode and multi-mode fibres routed adjacent to...

Collector Stations

WOW03 Offshore Substation

Walney Extension Offshore Wind Farm (Irish Sea), United Kingdom

330 MW 220 kV · offshore

Rating:330 MW · 220 kV

Location:offshore

WOW04 Offshore Substation

Walney Extension Offshore Wind Farm (Irish Sea), United Kingdom

330 MW 220 kV · offshore

Rating:330 MW · 220 kV

Location:offshore

Middleton 400 kV substation

Middleton (Heysham), Lancashire, UK, United Kingdom

659 MW 400 kV · onshore

Rating:659 MW · 400 kV

Location:onshore