Peter Unternaehrer

6.4 MVA resitive fault current limiter based on Bi-2212 superconductor

Abstract ABB has recently successfully developed and tested a single phase 6.4 MVA superconducting fault current limiter (SCFCL) demonstrator, which is based on a novel conductor design and innovative Bi-2212 ceramic fabrication technology. At present, it represents the highest rated power reported for HTS based SCFCL. The employed SCFCL component is a composite consisting of layers of bulk Bi-2212 ceramic, resistive metallic electrical bypass and fibre reinforced plastic (FRP). The Bi-2212 conductor is fabricated in sheets with an area of 30×40 cm2 by using a modified partial melt process and is subsequently structured into long length meanders. The as-processed Bi-2212 is non-textured and exhibits a uniform jc in the range of 3000–5000 A/cm2. The employment of a robust bypass facilitates a uniform quench in the SCFCL component during a fault event. Depending on the level of prospective fault current, a fault current is typically reduced to around 10 times nominal current in the first current peak and further to 2–5 times after 50 ms into the fault. Test and simulation results of the 6.4 MVA demonstrator, together with the application prospects of such Bi-2212 based SCFCL are presented and discussed.

Crystal field in RBa2Cu3O7 (R rare earth) determined by neutron spectroscopy

Abstract The crystal-field interaction of the high- T c superconductors RBa 2 Cu 3 O 7−δ (R  Nd, Dy, Ho) was determined by neutron spectroscopy. Here we summarize our results obtained for NdBa 2 Cu 3 O 7−δ . The observed energy spectra are strongly influenced by the oxygen vacancy concentration δ, and the quasielastic line width exhibits a sudden drop at T c .

Crystal field in HoBa2Cu3O7−δ determined by inelastic neutron scattering

Abstract Inelastic neutron scattering has been employed to study the crystalline electric field (CEF) interaction in the high-T c superconductor HoBa 2 Cu 3 O 7−δ . The CEF at the Ho site completely lifts the 17-fold degeneracy of the ground-state J-multiplet. The observed energy spectra exhibit a large number of well resolved CEF transitions between 0.5 and 73 meV, so that all nine CEF parameters required for orthorhombic symmetry have been unambiguously determined. The results are used to predict some thermodynamic magnetic properties of HoBa 2 Cu 3 O 7−δ as well as to extrapolate the CEF interaction to ErBa 2 Cu 3 O 7 .

Dynamics of atoms in YBa2Cu3O7−x

Abstract In order to get insight into the role played by the phonons in the superconducting phase transition, we have performed infrared reflectivity and neutron scattering experiments on single phase YBCO. The results, together with published Raman data, are used to determine the parameters of a rigid-ion model; the model reproduces qualitatively well the experimental well the experimental data. On the basis of our model we calculate the phonon dispersion relations and the density of states with contributions of individual sublattices. In addition patterns of atomic displacements of some important modes are discussed.