Millions of people were left without power for hours on the Iberian Peninsula when the Spanish electrical system failed on Monday at 12:33 pm.

The lights went out, including traffic lights, throwing roads into chaos; card payments became impossible; hundreds of flights were cancelled.

The grid was gradually restored and investigations into the cause are underway, although Portugal’s government and Spanish power company REE have already ruled out a cyberattack.

“All the necessary measures will be taken to ensure that this does not happen again,� Spanish Prime Minister Pedro Sánchez said on Tuesday 29 April.

In fact, in some ways, measures already are underway, in the shape of a major project to build an undersea powerline between Spain and France.

A tunnel construction site at one of the two stations that convert the direct current from the line into alternating current for the supply grids (Image: Bessac)

The �3.1 billion project to build the 400km-long line in the Biscay Gulf between Gatika in Spain and Cubnezais in France is being overseen by INELFE (Electricity Interconnection France-Spain), a company set up after a 2015 agreement between the two countries.

It involves four direct current (DC) cables in total, two per link, with a transmission capacity of 1,000 MW for each of the two links.

Once completed towards the end of 2028, it promises to improve the safety and stability of the electricity connection in the region and could help to prevent the sort of outages experienced in Spain and Portugal last week.

A total of 80km of cable will run underground from Cubnezais, followed by 300km of submarine cable, and then another 13km of underground link to the converter station at Gatika. Once complete, it will increase the exchange capacity between the two countries by 5,000MW.

A map showing the route of the interconnector cables between France and Spain. The project is due for completion in 2028. (Image: INELFE)

Specialist tunnelling and pipeline construction contractor Bessac, a subsidiary of Soletanche Bachy, is undertaking the work on the underground microtunnels and directed drilling. Cable-laying ships will lay the cables at sea. In general, the cables will be buried, except where the ground is too hard, in which case they will be covered.

In France, work began in October 2023, with work on sites where the cables make landfall in progress in Porge, in Gironde, and Seignosse and Capbreton in Landes ongoing until 2026.

On the Spanish side, work started in Maruri-Jatabe and Lemoiz for the terrestrial sections at the end of 2024.

Once micro-tunnels are completed, pipes will be laid in the ocean and inland, before electricity and optical cables are rolled out in those pipes.

Earthworks are underway for converter stations in Cubzenais, France, and Gatika, Spain. A consortium between Vinci Energies, Vinci Construction and Hitachi Energy are in charge of the design and construction of the converter stations.  

The tunnels have a diameter of three metres (Image: Bessac)

Cable laying at sea should be completed in late 2027, ahead of the converter stations in 2028.

Japanese pump manufacturer Tsurumi said it will be supplying its KTZ415 pump, alongside other models, for dewatering in three tunnels along the route.

Designed for extreme conditions, the KTZ415 has a maximum flow rate of 1,980 litres per minute and a head of up to 55 metres. It features a hermetically sealed power supply and ultra-hard materials such as silicon carbide, meaning the pumps are safe to run dry. Tsurumi claims it has been used in almost every major tunnel project in Europe.

Currently, the interconnection capacity between Spain and France is among the lowest of all the European countries and remains well below the 15% interconnection target for 2030.

While its construction has not come quickly enough to prevent last week’s extensive outage, it should mitigate against future power cuts when consumption is high or in case of a technical incident by allowing Spain to import electricity from France as required.

Bessac is using Tsurumi KTZ415 pumps to dewater the tunnels (Image: Bessac)