H.-W. Neumüller

380 kW synchronous machine with HTS rotor windings--development at Siemens and first test results

Applying HTS conductors in the rotor of synchronous machines allows the design of future motors or generators that are lighter, more compact and feature an improved coefficient of performance. To address these goals a project collaboration was installed within Siemens, including Automation & Drives, Large Drives as a leading supplier of electrical machines, Corporate Technology as a competence center for superconducting technology, and other partners. The main task of the project was to demonstrate the feasibility of basic concepts. The rotor was built from racetrack coils of Bi-2223 HTS tape conductor, these were assembled on a core and fixed by a bandage of glass-fibre composite. Rotor coil cooling is performed by thermal conduction, one end of the motor shaft is hollow to give access for the cooling system. Two cooling systems were designed and operated successfully: firstly an open circuit using cold gaseous helium from a storage vessel, but also a closed circuit system based on a cryogenerator. To take advantage of the increased rotor induction levels the stator winding was designed as an air gap winding. This was manufactured and fitted in a standard motor housing. After assembling of the whole system in a test facility with a DC machine load experiments have been started to prove the validity of our design, including operation with both cooling systems and driving the stator from the grid as well as by a power inverter.

Current capability of filaments depending on their position in (Bi,Pb)2Sr2Ca2Cu3O10+δ ‐multifilament tapes

The microstructures of single filaments of silver‐sheathed (Bi,Pb)2Sr2Ca2Cu3O10+δ‐multifilament tapes are investigated by polarized light and scanning electron microscopy. Large differences in the microstructure of filaments depending on their position in the cross section of the tape are found. The influence of this microstructure on the critical current density is investigated by magneto‐optics. A drastic reduction of the critical current density by a factor of about 10 of the outer, compared to the filaments in the center of the tape is observed.

Fabrication and critical current densities of 2223-BiPbSrCaCuO silver sheated tapes

Abstract BiPbSrCaCuO silver sheated tapes were prepared with the composition Bi1.8Pb0.33Sr1.93Ca1.93Cu3O9.89 and Bi1.8Pb0.4Sr2.0Ca2.2Cu3O10.3. The core thickness ranged from 70 ωm to 20 ωm. The formation of the 2223 phase starts from the 2212 compound by a liquid phase reaction and is strongly influenced by to the presence of silver. j c∥ ( B ∥ tape) can be related to j c⊥ ( B ⊥ tape) assuming that the field component B ∥ c axis alone controls jc(B,T). We have deduced an average misorientation of the c-axes of the platelet shaped grains of about ten degrees. This is confirmed by SEM analysis. In case of the lead-rich compound more than 70% of the samples with 20 ωm in core thickness showed critical current densities between 15000 A/cm2 and 25000 A/cm2 at 77K in zero field and the maximum values measured so far were 35000 A/cm2.

High-Temperature Superconducting Rotating Machines for Ship Applications

Main applications for rotating electric synchronous machines are given as generators and motors; a small niche can also be found in synchronous condenser-applications. High temperature superconducting (HTS) rotating machines show several significant advantages over machines built in conventional techniques. These are mainly increased efficiency, higher power density, and enhanced electrical stability. Especially for on-board applications, these properties may be decisive to save fuel and space and improve the capabilities. In the past, basic programs were carried out to demonstrate in principle the possibility to build such machines. Meanwhile these programs have shown great success and the feasibility of HTS machines for such applications has come into reach. For that reason developments for HTS machines in the megawatt-range are now being in progress, for propulsion purposes as well as for power generation applications. Started with the built of a 400 kW model motor that has operated successfully for more than two years, Siemens is now being engaged in the development of HTS machines for all electric ship application in the megawatt-range. A demonstrator for a 3600 rpm 4 MVA generator has been set up in the Nuremberg test facility for extended type and system testing. Results of tests with both machines will be presented. Technical implications of this new technology for ship-borne application will be discussed together with general economic assessments

Development and application of superconducting transformers

Superconducting transformers are an important innovation for future power transmission and transportation systems. Powerful, lightweight, energy-saving and environmentally friendly they offer enormous benefits compared to their conventional counterparts. Siemens is developing a 1-MVA demonstrator transformer for laboratory testing, exhibiting innovative features like horizontal design, cabled-conductor windings and a closed cooling cycle with sub-cooled nitrogen. Being one of the most promising applications Siemens has started a programme towards the development of on-board transformers for electrical rail vehicles. This paper summarises world-wide efforts in the development of superconducting transformers and reports on the progress achieved at Siemens.

Development of HTS power transmission cables

The Siemens company is developing a high-temperature superconducting (HTS) 110 kV/400 MVA cable for future power transmission systems in densely populated areas. The cable consists of coaxial conductors made of 2223 BPSCCO multifilament tapes, a LN2-high-voltage insulation, a flexible cryostat, terminations and a LN2 cooling system. This paper gives an overview on the project status.

Enhancement of critical current density jcm and pinning energy U in melt textured Bi2Sr2CaCu2O8+δ on Ag-tape by heavy ion irradiation

Abstract Irradiation experiments using 502 MeV 127 I ions were performed on 2212 BSCCO melt textured layers on Ag-tape to create well defined columnar amorphous tracks (diameter: 5–10 nm). These tracks should act as very effective pinning centers, especially if they are aligned in parallel to the magnetic field. Magnetization measurements resulted in an enhancement of the magnetization current density j cm within the whole temperature range of 4.2 K up to 60 K. Enhancement factors up to 10 3 were obtained in a magnetic field of 2 T at 30 K after irradiation. We investigated our samples at magnetic inductions up to 12 T; the j cm results will be compared with critical current densities j ct derived from transport measurements revealing a pronounced lower j c -enhancement due to irradiation. The evaluation of E ( j ) curves gives evidence that granularity can be neglected in unirradiated samples, on the other hand, obvious limits for the intergrain currents exist after irradiation. According to relaxation measurements of the magnetic moment before and after irradiation with different doses of 502 MeV 127 I the activation energy U could only be increased from about 30 meV to 70 meV at 10 K and 0.1 T. The small increase of pinning energies is explained within the pancake vortex model and is consistent with recent results found on Bi 2 Sr 2 CaCu 2 O 8+δ single crystals.

Ion irradiation of layered BSCCO compounds : flux line pinning and evidence for 2-D behaviour

Abstract Previous irradiation experiments with high-energy low-Z oxygen ions and fast neutrons on both polycrystalline material and single crystals of the 2212 BSCCO compound showed that the number of effective pinning centres could be increased and jc was enhanced particularly at low temperatures but the pinning energies were not significantly changed. Whereas these projectiles create only small sized and randomly distributed defects, high energy high-Z ions like 0.5 GeV iodine ions produce continuous tracks (5–10 nm in diameter) along their path in 2212 BSCCO single crystals. Assuming conventional core pinning, the activation energies should be high enough to overcome the thermal depinning problem at elevated temperatures. In contrast to these expectations, the magnetization measurements showed that measured pinning energies at low temperatures and small fields do not exceed 70 meV after irradiation. At T = 10 K the magnetization currents could be increased up to 107 A cm−2 but they decline rapidly with field. The small pinning energies can be explained theoretically if one assumes that the elementary depinning mechanism is controlled by the thermally activated depinning of individual pancake vortices located within the CuO2 double layers. The 2-D nature is the consequence of the pronounced superconducting anisotropy in the BSCCO compounds. This behaviour is also confirmed in transport current measurements jct of polycrystalline highly textured 2223 BPSCCO silver tapes irradiated with 0.65 GeV Ni ions. The jct(B,T) dependence was investigated for both the field orientations B | tape and B ⊥ tape.

Magnetic properties of Ln2−xCexCuO4−δ(Ln=Nd, Pr, Sm) in the superconducting and normal-conducting state

Abstract We report on magnetic properties of the electron-doped cuprates Ln 2− x Ce x CuO 4− δ with Ln=Nd, Pr, Sm in the superconducting and normal conducting state. The preparation process of Ln 2− x Ce x CuO 4− δ bulks (Ln=Nd, Pr, Sm), was in vestigated by means of TGA and X-ray analysis. The normal state magnetic susceptivility of Ce-doped Ln 2 CuO 4− δ (Ln=Nd, Pr) is described by taking into account crystal field effects on the Ln 3+ sites as well as the contribution of the Cu 2+ ions. Furthermore we present results for the upper and lower critical fields and calculate from these the superconducting parameters ξ, κ and λ in the framework of the anisotropic Ginzburg-Landau theory.

Angular dependence of critical currents and grain misalignment in Ag clad (Bi,Pb)2Sr2Ca2Cu3O10 tapes

Abstract Two-dimensional behaviour of the critical current in highly textured silver clad (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10 tapes was observed and analysed by introducing an effective grain misalignment angle, ϕ eff . This angle was found by SEM to be identical to the average crystallographic grain misalignment angle in the superconducting core. Furthermore, after fast neutron irradiation, which is isotropic, the J c of the tapes were modified by the introduction of artificiale defects, but the ϕ eff remained the same. This proves that the crystallographic misalignment of the grains determines the critical current anisotropy of the tape in a magnetic field, i.e. I c ( B tape plane) scales with I c ( B tape pane) with the factor sin ϕ eff . Therefore, ϕ eff is an intrinsic property of the tape. ϕ eff is found to be around 10° in different samples. We propose that this typical value is determined by intrinsic mechanical properties of the (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10 compound and is a result of the mechanical deformation of the tape during the tape fabrication. From a comparison of different samples, we propose that the pinning ability is the determining factor of J c when ϕ eff small enough.