V. Beilin

Superconducting FCL: design and application

Design, parameters, and application areas of a superconducting fault current limiter (FCL) are analyzed on the basis of the requirements of power systems. The comparison of resistive and inductive designs is carried out. An example of the effective application of FCLs in distribution substations is considered and the gain from the FCL installation is discussed. It is shown that an FCL not only limits a fault current but also increases the dynamic stability of the synchronous operation of electric machines. The calculation procedure of the parameters of an inductive FCL for a specific application case is described.

Critical current anisotropy in non-sintered metal-clad MgB2 tapes

Abstract Ag/MgB 2 , Cu/MgB 2 and SS/MgB 2 (stainless) tapes were fabricated by the oxide powder-in-tube method. X-rays diffraction studies showed the formation of moderate c -axis texturing in the MgB 2 core, which increases with the sheath strength and correlates with the core microhardness. Magnetization hysteresis loops of the tapes were measured for applied magnetic field ( H ) parallel and normal to the tape plane, in a wide range of H (0–5 T) and temperature (5–25 K). The critical current density ( J cm ), calculated using the extended Bean model, indicates the possible current limitation due to inter-particle links. Significant anisotropy in J cm is observed. The “parallel” J cm is one order of magnitude higher than the “normal” J cm which is of the same order of magnitude as transport J c in non-sintered tapes. This anisotropy is assumed to be originated from the weak large-scale connectivity (deformation-induced crack formation) in densified MgB 2 core after the rolling process.

Magnetic relaxation and pinning in Ag/Bi(Pb)SCCO tapes: deformation-induced effects

Magnetic hysteresis and magnetic relaxation in as-sintered and cold-pressed after sintering Ag/Bi-2223 tapes have been studied in the temperature range of 5-45 K for two field orientations: -axis and -plane. Significantly higher effective pinning energy, , for as compared to that for , is connected with the mechanism of intrinsic pinning for the vortex motion normal to the atomic planes. Cold pressing results in the reduction of magnetization and transport inter-granular currents due to the introduction of additional weak links and microcracks into a sample. For the case the drastic drop in relaxation rate as well as the increase in the field of the first large scale vortex penetration, , was observed after cold pressing, indicating the enhancement of intra-granular and surface pinning by generated defects. Accordingly , the increase of in the limit of low currents was observed after cold pressing. Warm pressing which normally generates significantly lower concentration of residual defects than cold pressing, does not result in any inhibition of relaxation. For in-plane field vortices penetration into a tape interior through microcracks is the dominating deformation-induced effect resulting in the acceleration of magnetic relaxation and the significant decrease of .

Applications of an HTS thin film switching element in the inductive current limiter

Abstract We report the results of the test of a new inductive fault current limiter (FCL), where a secondary coil is fabricated from a superconducting BSCCO wire short-closed by a thin film switching element. This switching element was fabricated from an YBCO thin film deposited on a sapphire substrate and covered by Au layer. Under fault conditions the switching element passes into the normal state, whereas the coil remains in the superconducting state in any operation regime. The FCL meets to the basic requirements of power systems: low impedance under a normal regime of the protected circuit; fast increase of its impedance and the current limitation during a fault; quick return to the initial state after a fault ceases. The parameters of a full-scale device are estimated.

Deformation-dominated texturing of superconducting filament in OPIT-fabricated Bi(Pb)SCCO-2223/Ag composite tapes

Texture formation in the ceramic filament of Ag/BiSCCO tapes was studied after cold rolling, uniaxial cold pressing and sintering by XRD /spl theta/-2/spl theta/ and /spl omega/-scan methods. More effective texturing of the outer layers as compared to that of the core interior was observed at the early rolling steps up to about 65% reduction in area. Texture inhomogeneity over the filament cross section is related to the inhomogeneous distribution of plastic deformation. Work hardening due to plastic deformation of non-sintered powder results in the broadening of X-ray peaks and an increase in microhardness. The recovery of these parameters occurs after annealing at the temperatures of 350-600/spl deg/C. The /spl omega/-scan studies revealed an improvement of c-axis texture by intermediate rolling compared to that in the as-sintered and pressed states. Deformation-induced texturing of the 2212-precursor is the main factor responsible for the texture of the final 2223-phase. The influence of Ag during the sintering stage is limited only to the outer layers of the filament; in the case of low preliminary deformation internal layers remained practically non-oriented.

Doping of BiSrCaCuO compounds with (V+Y), As, Sb, Pb, Cr and Ge

Abstract The effect of various doping elements such as (V+Y), As, Sb, Pb, Ag and Ge in range of 3–5 atom% on the phase stability of the high temperature superconducting (HTS) Bi - Sr - Ca - Cu - O system was investigated by preparing (1) small single crystals from flux solvents, and (2) thick films by doctor blade casting. It was found that the Bi2Sr2CaCu2Ox (2212) is the predominant phase in all doped samples Examples of HTS critical temperature Tc results measured by microwave absorption are 94 K for (V+Y), 78 K for As, 74 K for Ge. For the Sb doped compound a two phase BSCCO material was obtained with two Tc of 90 and 78°K in the proportion of 20 to 80% respectively.

Effects of deformation on current-limiting factors in Ag/BiSCCO tapes

Abstract I–V characteristics, transport critical current density Jc at 77 K in moderate magnetic fields and irreversibility fields were measured in Ag/BiSCCO-2223 tapes at various stages of the OPIT process. Intermediate deformation dramatically reduces Ic in as-deformed state while retaining a finite-size percolative channel for transport current after used pressing load up to 11 GPa. The channel has a similar fraction of strong links (45%) and vortex pinning characteristics as those in a non-deformed state. Combination of intermediate deformation with subsequent sintering improves pinning characteristics of the tapes, reasonably increases vortex-glass–vortex-liquid crossover field Hg and significantly accelerates Ic growth during subsequent thermal processing.

The blistering phenomenon in BiSCCO 2223 high-Tc superconducting tapes

The captions to figures 4 and 5 should read: Figure 4. An XRD-pattern of the Ag/ceramic interface for the cylindrical (a) and flat (b) samples after sintering for 50 h: , 2223; °, 2212. Figure 5. An XRD-pattern of the ceramic core of the cylindrical sample after sintering at 840 °C for 190 h: (a) Ag/core interface; (b) internal surface of the cylindrical cavity. , 2223; °, 2212. On page 552 the first line of the right column should read (figure 5(b)) instead of (figure 5(a)).

Microwave synthesis of high Tc superconductors

Abstract Preliminary experiments showed that it is possible to prepare precursors for YBa2Cu3O7−δ and for the BiPbSrCaCuO system by sol-gel or solid state reaction followed by microwave oven processing.

Magneto-Optical Investigation of Superconducting Materials

Review of magneto-optical imaging and electromagnetic measurements defect structures in superconductors exposed to different thermo-mechanical heat treatments is presented.