Nexans : Super cool power highways

Imagine a single power cable capable of carrying the combined output of several nuclear power stations over long distances with no losses and minimal environmental impact. That's the possibility offered by superconductor technology. And it could help overcome one of the major barriers to Europe's successful energy transition to sustainable low carbon generation. Because the transition is not only about establishing new energy resources, including wind and solar, it is also about modernizing grids to provide the additional capacity and flexibility needed. Furthermore, the best places to build renewable energy schemes are usually a long way away from major population and industrial centres so we need to find new, efficient ways of transmitting large amounts of power over long distances.

Superconductors are a special type of material that has no electrical resistance when cooled below a critical temperature, which can range from close to absolute zero (-273 °C) to a 'high' of -143 °C. In contrast, the resistance of traditional copper or aluminium wires causes them to heat up, losing energy. Over a long distance this energy loss through what is essentially a 'leaky bucket' can amount to some 10 percent, that means that the equivalent output of several of Europe's largest power plants is simply going to waste.

Superconductors are not new by any means - the effect was discovered as far back as 1911 - and they are well established in high-technology applications such as medical imaging and particle accelerators. So why aren't they already being widely deployed in power networks? The answer lies in the complexity associated with their cryogenic cooling systems combined with the high cost of exotic superconducting materials. The capability of superconductors has been established in commercial grid installations, notably Germany's Ampacity project equipped with a Nexans solution that continues to supply electricity to a downtown district of Essen. The implementation of similar systems is set to grow, in particular through the work carried out within the framework of EU-funded initiatives. The most recent of these is the 'Best Paths ' project in which Nexans is working in consortium with leading research institutes, industrial and engineering companies, energy providers and grid operators to create a new generation of affordable superconductor power cables.

The new-generation cable is based on magnesium diboride (MgB) a simple compound based on raw materials that are abundant in nature. The compound is easy and inexpensive to manufacture - making it much cheaper than existing superconductor materials. Best of all, it can be readily made into wires, which are of course the basis for power cables. The cable is housed in a thermally insulating tube cooled by helium gas known as a cryostat.

The Best Paths project is focused on the development of a superconductor cable suitable for use with the high-voltage direct current (HVDC) transmission systems that are regarded currently as the best technical option for the transmission of power over long distances. HVDC relies either on overhead lines that require pylons that intrude on the landscape or underground cables that can be very costly to install. Both the overground or underground options are also subject to transmission losses that increase as the length of the line increases.

The particular advantage of the superconductor cable is its capability to carry a very high current with no loss, resulting in a much higher power density. The Best Paths design will operate at 320 kilovolt (kV) and 10 kiloamp (kA) with a capacity of 6.4 gigawatt (GW) per bipole (a bipole is a two-cable system). To put that in context, the UK's new Hinkley C nuclear power stations will generate 3.2 GW. A conventional cable system capable of carrying this level of power would have a seven-metre wide installation footprint. The superconductor cable packs the same power into a corridor just 0.8 metre wide.

Christian-Eric Bruzek of Nexans reports that the Best Paths project is progressing well:

'Since Best Paths started in 2014, we have developed the basic design of the superconductor cable and have been very pleased with the performance of the material. In 2017 we are going on to subject a 20 metre length of the cable to rigorous laboratory testing.

'While it is enticing to think of a future in which superconductor cables carry power over hundreds of kilometers, that is unlikely to happen for some time. In the short term, superconductor cableswill have a definite role to play as part of an overall solution that also combines conventional overhead lines and underground cables.The superconductor cables will come to the fore in relieving congestion at 'pinch points' in the grid, where you need to get a lot of power moving through a restricted footprint. That could be for example when crossing a river or in repowering existing corridors to bring more power into urban areas where planning restrictions can make it virtually impossible to build new electricity infrastructure.'

Dr. Christian-Eric BRUZEK
Superconductor Activity Project manager at Nexans

Christian-Eric BRUZEK is Project Manager for the superconductivity systems at Nexans and has recently been nominated as 'fellow' expert for the Group. Since 2009, he has participated and led several national and international collaborative projects with universities and major research laboratories. Since 2012, he has been appointed as the Chairman of International Standardization Superconductivity Committee TC 90. He also chairs the French National Committee UF90. Christian-Eric has also supervised several PHD programs in metallurgy, materials for mechatronics and superconducting devices.

Christian-Eric was awarded in 1993 a doctorate in metallurgy and materials engineering degree. Technical manager at Alstom MSA for magnets and superconducting cables until 1998, he joined Alcatel Cable in 1999 to manage a division for the manufacturing of 'high-temperature' superconducting tapes and mineral insulated cables. From 2005 to 2008, Christian-Eric headed the Materials and Expertise division of the national testing laboratory (LNE).

Christian-Eric Bruzek has worked and led many industrialization programs leading to the manufacturing of the majority of industrialized superconducting materials. He has developed a strong expertise in innovation of high level industrial processes and products..

Christian-Eric is currently involved in Fault Current Limiters programs and HTS and MgB cables for power distribution and transmission, either on high voltage or on low voltage cables for grids, some industrial uses and transportation (ship and aircraft). He has also developed a strong expertise in cabling, modeling and overall cable systems designs.

Christian-Eric Bruzek is the author of more than 60 Peer reviewed papers and books. He has given several invited talks in conferences and technical seminars.