Demo 5 Special Workshop: superconducting cables for very high power

Via Melara 40 in La Spezia is the address of ASG Superconductors, and on 5 July 2018 it was where 60 participants heard the results of the fifth and last BEST PATHS demonstration. The special workshop, the final one in the series, was organised by Nexans, IASS Potsdam and ASG, and the day included a visit to Columbus Superconductors, the company making the magnesium diboride wire at the heart of the cable.

Demo 5 had set out to show that a superconducting cable could carry direct current at transmission scale. The loop it built and tested under high voltage, with two terminations and its cooling systems, was a monopole running at 320 kV and 10 kA, which works out at 3.2 GW. Experts from ten European countries had designed the system, insulation and terminations included.

The speakers

Christian-Eric Bruzek of Nexans, whose company led the demonstration, stressed the novelty: “We have for the first time designed a high-voltage superconducting cable system capable of operating in direct current, while all the existing projects only deal with alternating current.” The hardest part, in his account, was the high-voltage terminations that join the cable to the existing grid.

Giovanni Grasso of Columbus Superconductors spoke about the wire. Magnesium diboride is cheap to produce, and the company’s wires had already been proven in full-scale devices such as MRI systems, induction heaters and fault current limiters.

Grid operators, as future customers, closed the day with a panel. Massimo Rebolini, for Terna and as chairman of the CIGRE Italian national committee, said Terna judged innovative cables on four criteria: technology, environment, resilience and grid integration. Jean-Yves Astic of RTE was more specific about what it would take: “customised use cases, ranging from 63 to 320 kV including details on the exact costs, practical system operation as well as long term maintenance.”

The next step named by the project team was modest and practical: testing guidelines for HVDC superconducting cables, drawn up with a group of manufacturers.

The full account of the cable, from wire manufacture to the finding that superconducting links can already compete with resistive cables in dense urban areas, is on the Demo 5 page.