The Greenlink Interconnector Scheme (500MW) will transfer power using high voltage direct current (HVDC) via submarine and underground cables over approximately 200km between two converter stations located in Wexford, Ireland (EirGrid) and Pembroke, Wales (National Grid). The power will be able to flow in either direction, depending on supply and demand in each country. Keltbray Infrastructure was awarded the contract to deliver key civil engineering works on the Pembroke Converter Station.
Project Scope
The Greenlink Converter Station encompassed a multitude of complex structures and significant milestones. The scope of works included:
- Precast Control building
- Transformer blast walls
- Steelframe & cladding of other buildings
- Pre Cast trough units
- Construction of Precast concrete buildings
- Steel frame & clad buildings
- Formation of door and equipment openings within the structure
- External individual foundations to enable the installation of electrical equipment
- Water retaining structures & bunds
- Internal & external cableways and ducting systems
- Final connection of foul drainage systems
Our teams successfully delivered the pivotal Converter Station Control Room by implementing an innovative precast concrete solution, later clad to enhance programme efficiency compared to conventional in-situ concrete methods. The DC Hall, Converter Hall, and Storage Buildings were constructed as steel portal frame and clad structures through collaboration with our strategic supply chain partners.
Recognising the critical nature of the transformer yard within the project, we engineered a solution to prefabricate all the required steel rebar cages for each foundation. This initiative included the development of supplementary temporary works control measures, executed through the Wentworth House Partnership business, streamlining the installation of cages within shuttering and concrete pouring processes. This proactive approach not only saved valuable time but also ensured an excellent-quality finish for this integral project component.
Key Challenges and Solutions
Location
The project’s location posed several challenges to delivery, as converter stations are typically constructed in remote and rural locations. Pembrokeshire and the surrounding regions are sparsely populated, with a limited pool of suppliers to access for project delivery. Sourcing suppliers further afield risked causing delivery delays, increasing costs, and associated carbon impacts.
As there was only one viable concrete contractor in the region, there was a risk that they may not have the capacity to support the project at the commencement date. To mitigate this issue, we engaged with the contractor during the tender stage, outlining project requirements and proposed dates and obtaining quotes based on the supplied tender drawings. This early engagement allowed the contractor to prepare quotes and preliminarily reserve capacity in the event of a work award, securing the supplier’s availability.
Adverse Weather
Adverse weather conditions frequently affect the project’s exposed location on a coastal peninsula. Erecting cladding in high winds was difficult and potentially dangerous, causing multiple delays to this element of the project.
To mitigate this, we reprogrammed the works flexibly to accommodate delays and implemented proactive day-to-day management of the programme. Maintaining continued monitoring of weather forecasts, we planned cladding works during good weather windows, applying additional resources and weekend work to maximise the volume of cladding completed in these limited time frames. During adverse conditions, our team proceeded with tasks that could still be completed in poor weather, ensuring we kept to programme timescales.
Design Changes and Approval
Circumstances surrounding the design process also presented challenges. Siemens’ design team was based in Germany, and the design itself was developed by an organisation in India. This meant any design changes which needed review and approval could be delayed by differences, and approval could be delayed by differences in working practices and time zones across three countries.
In response, we established regular engagement times with both the site team and Germany to provide buildability advice, influencing design decisions and amendments at a time when all teams were available. We also maintained a collaborative ethos with the Siemens site teams to streamline communication and prevent further delays. This was achieved through regular on-site collaborative planning sessions and opening more informal communication channels to escalate information rapidly.
