Magnesium diboride promises superconducting cables for the grid
Superconducting transmission lines designed using magnesium diboride could offer advantages in efficiency and environmental impact for the electricity grid. Natalie Daniels reports.
To meet future energy demands, electricity grids in Europe will need to be updated and expanded to ensure increased transmission capacity. To do this, 10 partners are working on a superconducting cable demonstrator as part of the Best Paths project, which consists of five demonstration projects and involves 40 partners across Europe. The superconducting demonstrator is exploiting the potential of magnesium diboride (MgB2) for superconducting cables. The 20-metre long MgB2 prototype cable is intended to comply with the power network and will be operational at currents of 10 kilo-amperes with voltage of 320 kilovolts.
With the phase-out of nuclear power in Germany (see Materials World, October 2016, page 29), the country’s reliance on solar and wind power will result in the expansion of the local electricity grid, for which transmission systems will be essential. Cable manufacturer, Nexans, France, alongside CERN, Switzerland, MgB2 wire manufacturer Columbus Superconductors, Italy, the Institute for Advanced Sustainability Studies, Germany, and other research groups, designed the cable system that will be built and tested in Hannover, Germany. The first components have already undergone R&D, and tests on the cable system are due to begin in 2017.
Initial experiments on MgB2 cables were carried out at CERN in 2014, and found that the material showed promise as a superconductor for high-current applications. Adela Marian, Physicist at the Institute for Advanced Sustainability Studies and Scientific Coordinator for Best Paths told Materials World, ‘MgB2 is a relatively cheap and simple material to use. It consists of only two elements, magnesium and boron, which are abundant materials. It can be easily fabricated into wires unlike other superconductors, which are produced into tapes. These wires offer a lot of flexibility and can be used over longer distances.’
The experiment will demonstrate the transmission of 3.2 gigawatts, the equivalent output of three large power stations, through its superconductive cable. This cable will be housed in a cryogenic tube along with its cooling fluid, which will keep it at an optimal temperature of 20K (around -250oC). ‘We specifically designed the wire, taking into account the transport current and the operation conditions in the grid. Once we had designed the wire, we ran simulations to make sure all the requirements imposed by the grid were met. It has taken several trials to find the right one.
‘Columbus Superconductors has manufactured several tens of kilometres of this wire, which is assembled into cables, consisting of several wires wound around a copper core. First validation tests of their mechanical suitability were already carried out by Nexans on industrial cabling machines.’
The research consortium will now work on testing the cable using two different methods. ‘We are first going to test the high-current capability at CERN, as they have the facilities for such experiments, which not all labs have. Then the high voltage tests will be completed at Nexans in Germany, as their facility can reach more than 500 kilovolts for the testing of our prototype.
‘The next step after Best Paths is to take this research from the laboratory and into a real grid to monitor how it behaves for longer periods of observation. There are already superconducting cables in the grid, based on different materials and different operation parameters that have been shown to work already. We don't think there will be problems connecting this new technology, but now it is important for us to complete the tests.’
RTE, the transmission system operator in France and a partner in Best Paths, has already expressed interest in the technology and is providing guidance for the grid integration, along with an economic viability analysis of the superconducting power cable.