The Western High Voltage Direct Current (HVDC) Link is a major electricity transmission project being jointly developed by National Grid Electricity Transmission and Scottish Power Transmission. This £1 billion project is going to help bringing renewable energy from Scotland to homes and businesses in Wales and England. Worthy of note is that it sets a record in terms of voltage due to its 600kV and has a currently unmatched transmission capacity for long-haul systems of 2,200 MW. 

The Western Link project includes direct current subsea and underground cables. It consists of approximately 422km of cable, of which 385km are underwater. The link connects England with the landfall of the Wirral Peninsula and Scotland with landfall at the Hunterston area.

Throughout the UK, electricity is transmitted by alternating current. This project therefore incorporates a converter station at each end of the link to change the electricity from direct current to alternating current to enable it to be used within the existing electricity transmission system.

Prysmian awarded ASDG with a subcontract for the submarine cable laying and protection for the Western HVDC Link project at Wirral. ASDG’s SoW included cable loading of 2x36.2km HVDC and 36.2km FOC and simultaneous laying and burial operation of the bundled cable cable from Rev KP 0.0 to Rev KP 36.2 from Wirral landfall (KP 350.9 to KP 387.1). The SoW also included assistance to cable pulling to shore up to the sea-land joint position, pre-lay grapnel run, the performance of a visual pre-lay survey and the execution of post-lay seabed survey.

This project is considered a major challenge for ASDG.

'Atalanti' having all cables onboard was literally grounded approximately 1.1km seaward of the Leasowe sea wall for several days. As risky as it sounds, it was the only option available for the cable laying barge to be as closer as possible to the end of the 600m plastic pipes that were installed in 2013 to carry the cable beneath the seawall at Leasowe.

The two power cables in bundle with the fiber optic were then paid out from 'Atalanti' and reached the start of the plastic pipes using a special rollerway which was temporary structured on the shore to facilitate the cable landing. The rollerway length was 600m and the operation was only possible at times of low tide and both the vessel and the equipment were reliant on the weather.

As the 'Atalanti' was positioned almost 1.1km away from the area of operation, it was impossible to assist the landfall cable protection. The support barge 'Richoula' was specially designed and constructed for this project as it carried the spread of the 'AssoPlow MK II' during the cable protection nearshore.

Once landing operation was completed, 'Atalanti' was then started simultaneously laying and burying the bundled cables from the Liverpool Bay towards the offshore. In deep water burial the 'AssoPlow MK II' was disconnected from the support barge 'Richoula' and all operations were then transferred to 'CLB Atalanti'.

During the SLB process the weather became unfavorable with winds of over 100 miles per hour and waves as high as 10 meters. Due to lack of flexibility and maneuverability of 'Atalanti' as she was literally tied to the cables, it was decided to surface-lay the bundle and after the storm recovering it and proceed on protecting it.

At very small and rare parts were the SLB process was not able to successfully protect the bundle, the 'AssoJet II' was used to bring the cables at the required depth.

This project is considered a major project for ASDG successfulness throughout these years. It simply demonstrated for once again that we do offer customized solutions to our Clients and we are able of accomplishing complex projects in a resourceful manner and always in line with quality, safety and time.

 

Watch a nice time-lapse video on the following link: Atalanti on WesternLink Landing

 

Project Specifications

Western HVDC Link

Year:
2014
Contractor:
Prysmian PowerLink Srl
Cable Type:
Power 2 x 600kV HVDC & 1 FO
Cable Weight:
Power: 57.7Kg/m FO: 3Kg/m in air
Cable Diameter:
Power: 137mm FO: 35mm
Service Provided:
Cable Transportation ‐  Simultaneous Laying/Burial
Laying Length:
36,200m
Owner:
National Grid Electricity Transmission & Scottish Power Transmission
Jetting Length & Cover Depth:
21,200 @ 2.0m 15,000 @ 3.0m
Location:
Wirral Peninsula, UK
Max Water Depth:
30m