Five grid transmission technologies, tested between 2014 and 2018

A transmission operator has three ways to move more power across a continent: build new lines, get more out of the old ones, or use a different kind of current. The five demonstrations below cover all three. Two concern high-voltage direct current where it meets offshore wind and where equipment from rival manufacturers has to share one grid. One looked at renewing an ageing multi-terminal DC link with new components. One put new conductors, insulators and live-line methods on existing AC routes. The last tested a superconducting cable that could carry gigawatts through a single narrow circuit.

The project behind them ran from late 2014 to 2018 with close to 40 organisations from research, industry and grid operation, coordinated from Spain. Its own summary was blunt: the aim was more pan-European transmission capacity and more flexibility without losing reliability.

What each demonstration tested

Demonstration 1, led by the Spanish utility Iberdrola, dealt with the far end of an offshore wind connection. Farms a long way out in the North Sea come ashore on direct current, because an AC cable of that length spends most of its capacity charging itself. The weak spot is the meeting point between the power electronics in every turbine and the big converter at the offshore substation. The demonstration studied how the two disturb each other, and how more suppliers could be brought into a market that a few manufacturers dominate.

Demonstration 2 put that supplier question to a direct test. In a laboratory run by RTE, the French grid operator, control cubicles from ABB, Alstom Grid and Siemens were wired into one real-time simulation of a DC grid. Every VSC link in Europe up to then had come from a single supplier, both ends included. The results, shown in Paris in June 2018, located where converters from rival makers clash and what it takes to make them work together.

Demonstration 3 used a working line as its test bench. SACOI runs from Sardinia through Corsica to the Italian mainland, and Terna, which led the work, calls it the first multi-terminal HVDC system in the world. It dates from 1967–68, and its replacement is now under construction. The demonstration designed and tested the components that a modern three-terminal link would need.

Demonstration 4, led by the German operator 50Hertz, stayed with alternating current. It worked on high-temperature low-sag conductors, insulated cross-arms, live-line methods and a dynamic line rating system built from low-cost sensors. All of them get more power through a corridor without adding towers, and the page includes a span that can be loaded until it sags into the trees.

Demonstration 5, led by the cable maker Nexans, built a superconducting cable from magnesium diboride for direct current. A single wire carried 700 amperes without warming, and the full system was designed for 320 kV and 10,000 amperes, 3.2 GW in one circuit. The demonstration closed at a workshop in La Spezia in July 2018.

Where the technologies stand

The big links finished since the project closed follow the familiar pattern. ALEGrO in 2020, NordLink and North Sea Link in 2021 and Viking Link in 2023 are all voltage-source links with two ends, each with its converters from one supplier: Siemens Energy for two of them, ABB, now Hitachi Energy, for the other two.

The oldest of these questions is the least settled. Europe now operates dozens of HVDC links, listed with their figures on the power-link map, yet most of them are still point-to-point connections, and a DC grid shared by equipment from several makers remains rare.

Each demonstration page covers the problem it addressed, who led the work and what was built or tested, and ends with the project record: the workshops and news items where the results were first shown, with their original dates. The project page has the budget, the partners and the conclusions the consortium drew in 2018.