Superconducting YBa2Cu3Oy (YBCO) foams were prepared using commercial open-cell, polyurethane foams as starting material to form ceramic Y2BaCuO5 foams which are then converted into superconducting YBCO by using the infiltration growth process. For modelling the superconducting and mechanical properties of the foam samples, a Kelvin-type cell may be employed as a first approach as reported in the literature for pure polyurethane foams. The results of a first modelling attempt in this direction are presented concerning an estimation of the possible trapped fields (TFs) and are compared to experimental results at 77 K. This simple modelling revealed already useful information concerning the best suited foam structure to realize large TF values, but it also became obvious that for various other parameters like magnetostriction, mechanical strength, percolative current flow and the details of the TF distribution, a refined model of a superconducting foam sample incorporating the real sample structure must be considered. Thus, a proper description of the specific microstructure of the superconducting YBCO foams is required. To obtain a set of reliable data, YBCO foam samples were investigated using optical microscopy, scanning electron microscopy and electron backscatter diffraction (EBSD). A variety of parameters including the size and shape of the cells and windows, the length and shape of the foam struts or ligaments and the respective intersection angles were determined to better describe the real foam structure. The investigation of the foam microstructures revealed not only the differences to the original polymer foams used as base material, but also provided further insights to the infiltration growth process via the large amount of internal surface in a foam sample.

The use of High Temperature Superconducting (HTS) cables as a technology is considered as key to increasing the power of the electrical grid while reducing the volume of installation. In addition, when transmission currents exceed a few kA, DC HTS cables significantly reduce power losses, rights-of-way and total system mass. This article describes the various studies that need to be carried out in order to correctly size HTS DC cables for the new railway network envisaged by the French company SNCF, which must consider ultra-urban needs. The process used to design DC cables for operating powers of 10, 20 and 30 MW at a nominal voltage of 1.5 kV using commercial (RE)BCO tapes is presented. In this sizing process, the critical current density Jc(B, θ, T) dependence of the superconducting tapes, the thermal properties of the materials and the different cooling modes are taken into account. Several solutions are suggested to ensure that the cable can withstand fault currents and reduce recovery time in the initial state. Finally, with the help of analytical models and industrial data, once the cables have been designed, the various system losses are reported as well as the power or size of the various auxiliary components.

The use of High Temperature Superconducting (HTS) cables in power systems increases transmission capacity whereas reducing the volume of the installation. In addition, when transmission currents exceed a few kA, HTS DC cables significantly reduce power losses, right-of-ways and total system mass. This summary describes the various studies to be carried out in order to correctly dimension DC HTS cables for the new railway network envisaged by the French company SNCF, which has to take into account the ultra-urban needs. The process used to design DC cables for different operating current values between 5 kA and 20 kA at 1 750 V using commercial (RE)BaCuO tapes is presented. In this design stage, the dependence of the critical current density Jc(B, θ, T) of the superconducting tapes, the thermal properties of the materials used, and the different cooling modes as a function of the cable length are taken into account. Finally, we discuss a cryogenic solution to protect the cable in case of short-circuit or overload.