NG Worker marine survey vessel; Source: EirGrid/RTE

Offshore cable installation for France-Ireland interconnector on track to kick off next year

As the energy transition makes inroads on the global scene, subsea interconnectors are gaining popularity. One such project under development is the Celtic Interconnector, designed as the first subsea cable foray in linking the power systems of Ireland and France to enable the exchange of electricity between the two countries. This project is already starting to take shape and the offshore cable installation work is slated to begin in 2025.

NG Worker marine survey vessel; Source: EirGrid/RTE

While France’s Nexans has started the installation of the high-voltage alternating current (HVAC) onshore cable in Ireland, works at the converter station in France are also progressing and are said to include an eco-design approach with more than 50% low-carbon concrete and more than 60% recycled steel being used. After the beginning of work along the cable route in early April, the selected installation method is perceived to be reducing the amount of concrete required.

The marine cable preparatory work for the Celtic Interconnector, being developed by the Irish transmission system operator (TSO) EirGrid and its French counterpart Réseau de Transport d’Electricité (RTE), is ongoing in France with the ducts to protect marine cables assembled and set to be transferred to the landfall point in Cleder, Brittany, later this month.

Furthermore, the onshore cable works such as trenching and ducting for the project, which have already commenced and are nearing completion along the HVAC route, represent the first stage of roadworks and require temporary road closures on local roads. The second stage will entail cable pulling and cable jointing before all works on the road are over.

The 400 KV HVAC cable installation, which began in April, was the first of 91 power cable installation operations required to complete the 43 km land-based cable route on the Irish side of the project. Cabling crews began working west to east on local roads, from the network connection side of the project, towards the submarine cable interface at Claycastle Beach, Youghal.

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Based on the most recent project update, the second phase of cable laying has begun in sections of the route where the ducting is already installed in the trench, which requires the cable to be pulled through the lengths of ducting and into the jointing bay where one length of cable will be jointed or connected onto the next.

Given the production and transport limitations for the cable, lengths of approximately one kilometer are produced, thus, a cable joint operation needs to be carried out at around every 1,000 meters. Samples were taken from two trenches on the line of the cable and numerous wood samples which are now ongoing further examination to inform a potential further archaeological excavation that would take place in autumn 2024.

While the construction works continue at the converter station site at Ballyadam, outside Carrigtwohill, the excavation of the converter station control building is seen as the start-up of main civil works. Siemens Energy has picked Wills Bros as its sub-contractor to construct the converter station. The build-up of the converter station site to the platform level has so far been completed with underground services installed in preparation for pouring concrete foundation slabs.

Recently, Greece’s Asso.subsea disclosed that it would pool resources with Nexans to perform subsea burial operations for Ireland’s first power connection with continental Europe. Currently, marine surveys, undertaken by the French cable maker with support from Next Geosolutions, are taking place between the southeast coast of Ireland and the French coast within the cable corridor extending around 50 meters on each side of the centerline of the proposed cables.

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Moreover, the NG Worker survey vessel embarked on its marine surveys on May 8 in the Irish nearshore. These activities include potential unexploded ordnance (pUXO) and geophysical surveys within Youghal Bay before heading offshore for a geotechnical survey. The Detector OoS cable-cutting vessel is said to be performing well and making good headway in French waters before making its way through UK waters and into the Irish offshore area.

EirGrid and RTE underline that the vessel is around 50% through the entire cable route for the OoS operations, adding that some other vessels will be joining the fleet for the upcoming pre-trenching and boulder clearance works anticipated to kick off in Irish waters mid-summer to take advantage of favorable weather conditions.

Based on the current project timeline, 2024 has been designated as a year in which marine surveys, continuation of trenching and ducting works for HVAC and HVDC land cables, start of installation and jointing of HVAC and HVDC land cables, and converter station installations progress will be in focus.

The start of offshore marine cable installation is planned for next year along with the completion of installation and jointing of HVAC and HVDC land cables and converter station buildings. Finally, the completion of offshore marine cable installation, submarine cable protection campaigns, commissioning tests, interconnector system tests, and the start-up of the trial operation period are also scheduled for 2026.

Courtesy of EirGrig/RTE

A total of 48 high voltage alternating current cable drums were delivered by sea to Cork Harbor last January to be installed on the road east to west from the Knockraha substation. The submarine cable for the Celtic Interconnector project is expected to be manufactured by Nexans in a tower that is 152.89 meters tall and deemed to be Norway’s tallest building and first skyscraper.

The Celtic Interconnector project will link the existing electricity substation in Knockraha located in east Cork to the substation in La Martyre in Finistère, France, contributing to not only a more secure but also sustainable electricity supply by providing Ireland’s only direct energy connection to a European Union (EU) member state. Spanning 575 kilometers, the project, which was awarded €530.7 million in Connecting Europe Facility (CEF) funding in 2019, is expected to be completed in 2026.

The Celtic Interconnector is described as constituting a high voltage direct current (HVDC) connection across the Celtic Sea, from east Cork, Ireland, to the northwest coast of Brittany, France, of which the offshore element comprises approximately 500 kilometers. Upon completion, the 700 MW 320 kV VSC HVDC link is set to allow the movement of enough electricity to power 450,000 homes.