Interconnexion France-Angleterre 2 (IFA2)

Multidisciplinary design of technically challenging and complex HVDC convertor station, connecting the French and UK electricity systems

First of a kind solutions, with two layers of RFI Shielding required to mitigate electro-magnetic impact on surroundings

Delivered to a tight design and build programme

A technically challenging and highly complex project, the new onshore HVDC converter station in Lee-on-the-Solent is part of the wider Interconnexion France-Angleterre 2 (IFA2) project to link the French and UK electricity networks. The new 1,000 MW 320kV HVDC electrical interconnector will have the capacity to power up to a million homes with clean energy, providing greater security of supply, affordability and sustainability through linking the two networks.

BakerHicks were appointed to deliver multi-disciplinary design services, including architectural, civil and structural engineering, mechanical and electrical engineering, and construction support. Key services included:

  • Design of the new valve, reactor, AC and DC process hall buildings, facilitating the HVDC equipment, including climate system and dehumidification design for process halls.
  • Design of steelwork, building envelope, small power and containment, HVAC, auxiliary electrical systems, and internal and external lighting for all buildings.
  • RFI shielding detailing for process halls, including two layers of shielding in the DC, valve and reactor halls.
  • Design of duct and troughs for converter station including all routing based on concept HV designer requirements. Included deep AC, GIS and DC cable trough design and detailing of EMC and earthing design.
  • Super Grid Transformer and shunt reactor bund designs, and design of liquid retaining glycol cooling bund.
  • Design of internal road for abnormal indivisible load (AIL) vehicles including S278 works and approval, all drainage systems and perimeter security fence.
  • Planning permission approval support and drawings.

Planning conditions for the project were difficult due to the proximity of a residential area. BakerHicks took the lead in producing planning sketches and worked closely with the Local Planning Authority to obtain approval. The design from these sketches was implemented in the final build of the station.

First-of-a-kind solutions

With the converter station located on an operational airfield and close to a residential area, the potential impact of electro-magnetic interference was a key concern. BakerHicks worked closely with all stakeholders to ensure the design had the correct levels of RFI shielding to ensure it did not have a negative impact on aircraft or residents’ television signals. Two layers of RFI shielding were required, a level of integration that had never previously been done. Our team carried out extensive research, working closely with the equipment manufacturer’s HV design team to ensure the requirements were met without impacting on the buildability or operability of the buildings and processes.

The RFI requirements had a significant impact on the choice of materials and structural design of the buildings that comprise the converter station. Our structural engineers used specialist frames, which are EMC suppressed and physically bonded to the structure and aluminium, meaning any interference would be confined within the space. One of the key challenges was that the shielding needed to be throughout the building without interruptions to create the Faraday Cage, but services also needed to pass in and out and the building materials needed to be able to expand and contract in reaction to the heat generated by the HV processes. This usually requires joints to be incorporated into the building materials, but the RFI requirements prohibited this. Our structural engineers developed a bespoke solution that would allow for these requirements whilst still protecting the integrity of the Faraday Cage.

To further mitigate the impact of any potential impact on the working airfield, our architectural team also worked closely with the planners and stakeholders to devise a scheme that took into account the colours of the building envelope and their reflective values.

Collaboration

With the new converter station project providing the connecting point between multiple aspects of the wider project, plus a tight programme to be met, the design had to be carefully coordinated. BakerHicks were proactive in collaborating with the wider team, client and stakeholders, holding regular review meetings and workshops, both in the UK and in Sweden, to ensure everyone’s needs were met and the project was managed effectively.

An open technical exchange with the Swedish based HV design team played an essential role in ensuring all aspects of the design met the complex needs of the internal equipment. With technology for HVDC design continuously evolving and improving, this was especially important. It meant BakerHicks had to be proactive and flexible in the design processes, with significant changes occurring as the design developed. This close working relationship with the HV team, plus working in a 3D environment for all aspects of the design, meant all changes were managed without delay to the programme. Integrating all designs into one federated model, managed by BakerHicks as Building Information Modelling (BIM) coordinators, ensured clashes were minimised and aided coordination between the wider design team.

Meeting rigorous standards

With relatively new technology being used, plus the project’s importance to the national infrastructure, rigorous security standards had to be met.

All buildings needed to comply with stringent CPNI standards for the internal, envelope and door design, so our team worked closely with the contractor, supply chain and stakeholders to ensure all elements met the desired standards. For example, a rigorous testing process was employed to select a supplier for the doors in order to ensure the selected company could provide doors that met the required standards and fit the space.

Efficient, easy to maintain systems

Efficiency, future operability and ease of maintenance were key considerations in the design. The technology and processes inside the buildings generate substantial amounts of heat so all mechanical solutions in particular needed to be extremely efficient to keep the internal environment within the required zones. To achieve this, our mechanical engineers designed a HVAC system that exhausted the heat and pumped in fully conditioned outdoor air. This allowed the internal environment to be kept at a positive pressure and a low air leakage rate. All these areas were also designed with a resilience system in place, ensuring the station can be kept operating at all times.

The electrical distribution systems supported ease of maintenance and provided future proofing through a plug and play modular system. This allows sections to be isolated one at a time, offering ease of maintenance and ensuring constant operation. It also ensures final circuit protection and is easily expandable, enabling it to be adapted to work with any future developments.

Delivered to a tight design and build programme and to an exceptionally high quality, the new IFA2 converter station provides the UK link in the wider programme to connect France and the UK’s electricity systems. Ultimately, providing more sustainable, affordable and secure power for both nations.