Subsea Transmission Link to Propel UK and France to Zero-carbon Economy

March 09, 2023 by Stephanie Leonida

The UK High Court supports the development of the UK-France Aquind Interconnector, a subsea transmission link capable of delivering up to 17 terawatt-hours of electricity per year.

The UK High Court has shown support for the development of the largest electricity interconnector in Britain, based on capacity. The High Court’s decision supersedes the then Secretary of State for Business, Kwasi Kwarteng, who refused the Development Consent Order for the Aquind Interconnector early last year. The £1.35 billion submarine interconnector will use voltage source converter (VSC)-based high-voltage direct current (HVDC) technology to control power transmission between Britain and France.


Schematic depicting the basic geographical layout of the AQUIND Interconnector. Image used courtesy of Aquind Limited


Achieving Climate Neutrality

Climate neutrality is a concept whereby greenhouse gas emissions are reduced to net zero, meaning that the same amount of emissions produced is offset by activities that absorb or reduce an equivalent amount of carbon dioxide from the atmosphere. The UK and the European Union are striving to achieve climate neutrality by 2050 by investing in technologies and projects that reduce emissions, capture, and store carbon.


Interconnectors for a Zero-carbon Economy

A congested electricity network is a situation where the energy infrastructure cannot cope with the amount of energy being used. This can occur due to poor energy infrastructure where there is a lack of investment in energy storage, management, and upgrades to existing grid facilities. Congestion can lead to power outages, blackouts, and higher electricity prices.

According to the South East Local Enterprize Partnership (South East LEP), the southeast of the UK ranks third for its capacity to produce electricity from renewable sources. A majority of the electricity coming from this region stems from its solar photovoltaic schemes, delivering as much as 36 percent more electricity than other regions in the UK.

Having the capacity to generate this much electricity is all well and good, but can the local electricity network and main power grid handle the dynamic shift in load? How will electricity transmission be managed effectively? This is where the Aquind Interconnector project comes into play.

Interconnectors are a key enabler of the energy transition, providing a way of integrating renewable energy resources while managing power generation and transmission to achieve an optimum level of efficiency. The technology can help power system operators adapt to changes in energy demand across sectors such as transport and industry.


The Aquind Interconnector

The Aquind Interconnector will run from the National Grid’s Lovedean substation in Hampshire to the Barnabos substation managed by France’s transmission system operator, Réseau de Transport d'Électricité or RTE.

The interconnector will use VSC-based HVDC technology, a modern power transmission system that uses direct current (DC) instead of alternating current (AC). It is suitable for long-distance and high-power transmission. VSC-based HVDC technology utilizes two VSCs connected at each end of the transmission line to convert the AC power from one end to DC power at the other end. This DC power can then be transmitted over long distances with minimal losses and converted back to AC for use in local distribution systems.


Schematic depicting the structural materials of the AQUIND Interconnector cables. Image used courtesy of Aquind Limited


The Skin Effect

Unlike HVDC systems, HVAC networks are prone to the skin effect phenomenon, which occurs when electric current flows through a conductor, such as an overhead power line or underground cable. As the current moves through the conductor, it creates an electromagnetic field around it. This field affects the flow of electrons within the conductor, causing them to move closer to its surface. This increases resistance at higher frequencies and causes energy losses due to heat generation. HVDC uses insulated cables, which reduce the electric field and prevent the current from spreading out. This is what allows for more efficient transmission of electricity over long distances. 

The Aquind Interconnector will use next-generation power electronic converters with redundant units and hundreds of sub-modules. If just a few modules fail, other functioning modules will keep the station operating at full power. Aquind will integrate two separate 1,000 MW links to avoid interconnector loss should a single disruptive fault occur.

Each converter station will connect to a remote station via two pairs of HVDC cables, traversing underground and underwater between the coasts of the UK and France. The cables feature a copper core enclosed in a plastic-based insulating layer called Cross-linked Polyethylene (XLPE). This structure allows the cables to run at ± 320 kilovolts and a steel wire armor will encase marine cables to prevent damage during cable-laying by a marine vessel.


Featured image used courtesy of Adobe Stock