Periodic Reporting for period 3 - FASTGRID (Cost effective FCL using advanced superconducting tapes for future HVDC grids)
Berichtszeitraum: 2019-07-01 bis 2020-11-30
In short, FASTGRID made possible a leap forward in the performances and cost of SFCL besides the numerous advances about CFD implementation, quench detection, sapphire substrate tapes, high cp shunt, simulation and experimental tools… All the more there is a clear and real demand today for SFCL. Many transdisciplinary works and great collaborations between partners were carried out. Most of these advances are valid for other SC applications so the exploitation of FASTGRID goes beyond SFCL. The works do not stop with the end of FASTGRID. Many of us, companies inter alia, are convinced about the interest of the developments that will be pursued. FASTGRID was a fantastic and essential trigger.
The conductor has been used to wind two 5 kV coils fully representative of future SFCL basic elements. These two coils were successfully tested in Berlin at IPH.
A thorough and unique Life Cycle Analysis (LCA) was carried out on the THEVA and OXO tapes. This LCA has quantified the large environmental advantage of a SC conductor compared to a copper one for most categories, especially acidification (20 %), freshwater ecotoxicity and eutrophication (30 %), marine eutrophication (25 %), particulate matter (20 %), photochemical ozone formation (30 %)…
Even if the developed conductor shows secure operation whatever the fault conditions are, FASTGRID has implemented the CFD (Current Flow Diverter) proposed by EPM in the tape architecture. This patented configuration makes possible to significantly enhance the Normal Zone Propagation Velocity (NZPV) and so the security of operation by spreading the energy dissipation. The CFD is based on a thin electrical insulating layer over a large part of the interface between the superconducting and metallization layers. Several strategies have been investigated. The most promising is based on a silver sulfide insulating layer whose industrial implementation is rather easy. This time the CFD effect was clearly experimentally demonstrated. The exploitation of a CFD tape may be broad: the CFD process could be included in the future for all Coated Conductor REBCO tapes.
Beside the Hastelloy® shunt route, conductive polymer-based shunts were investigated to reach even higher electric fields. This high cp shunt is made of epoxy resin combined with ceramic fillers (Al2O3, SiC, glass fibers) to fit the thermal expansion of the tape. Reduction of the maximum temperature reached during limitation process has been confirmed experimentally. FASTGRID has demonstrated the possibilities of this emerging solution.
Sapphire substrate tape is a total game-changing technology to reach ultimate electrical fields, at least one order of magnitude higher (2 kV/m experimentally measured) than with Hastelloy®-based tapes, while presenting intrin¬sically high NZPV. This route was at a low TRL level at the beginning of FASTGRID which aimed to develop this breakthrough route and increase its TRL. The studied architecture is sapphire/YSZ/CZO/YBCO; it has been thoroughly investigated. FASTGRID made possible a lot of advances about the sapphire route both from theoretical and elaboration points of view. Several phenomena are much better understood. Pieces of 1 m have been produced. The next challenge is the reel-to-reel manufacturing but FASTGRID paved the way in this direction.
A highlight of FASTGRID is the patented optical fiber sensing technique to quickly detect a hotspot whereas the detection system is very low cost with a simple implementation. This new technique, based on Mach-Zehnder technique, was validated on a few meters (2 x 6 m). The hot spot detection time is within 10 ms. As for the CFD implementation, this hot spot detection system has a great potential of exploitation for most SC applications.
Thanks to FASTGRID, recommendations were developed to test DC SFCL and we think that these recommendations will become standards soon.
Thanks to FASTGRID and a better understanding of the process, the THEVA production line of REBCO SC tapes has progressed a lot with an increase of the critical current (+ 80 %) and its homogeneity (from 10 % down to 3-4 %) along its length. The impact of these significant advances oversteps the SCFCL domain. These advances are very important for nearly all applications of the tapes and they enhance THEVA’s competitiveness at international level.
The successful implementation of the Current Flow Diverter to enhance the Normal Zone Propagation Velocity experimentally by one order of magnitude in another important impact and outcome of FASTGRID, all the more the CFD tapes are of large interest for most SC applications, not only for SFCL.
NEXANS, as SGI industrial shareholder, has gained in competitiveness in SCFCL thanks to the optimized lower price conductor developed within FASTGRID for medium voltage SCFCL on the shelf today.