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High temperature superconducting (HTS) rotating machines show several significant advantages compared to machines built in conventional technique. Former experiments on rotating electric synchronous machines like motors and generators in the power range up to several MW confirmed the well-known benefits of HTS machines like smaller size, less weight and last but not least, a significantly increased efficiency. Especially the increased efficiency of large HTS-Generators up to several hundreds of MW-as operated by utilities-promises an efficient use of fuel and energy sources. This will allow reduced carbon dioxide emissions and becomes more and more important. The development of HTS rotor technology for generators in the range of hundreds of MW bears new challenges. HTS generator windings capable to withstand large centrifugal forces and carrying large currents are required. Also a special cooling system for the rotating winding and further components with novel design will be necessary and have to be developed. In a future HTS generator based on such components, these will have to operate very reliably, so a facility is needed to be able to perform tests. Therefore it is essential to design and build a specific test rig for investigation and test of the required new components. The present paper deals with design and development of such a test rig that allows component tests under realistic conditions, using radii in the range of 0.45 m as in a generator application at rotational speed of up to 3000 rpm, and at low operating temperatures of about 30 K. Additionally a 3 kA high current power supply for HTS test objects like coils or contacts is projected. Aspects of rotor dynamics and fatigue strength analysis had to be considered.

We investigate the use of 2nd-generation High-Temperature Superconductors (2G-HTSs) in the rotors of electrical motors and generators. For these devices the conductor must be wound into robust impregnated coils, which are operated in vacuum at temperatures around 30 K, in strong magnetic fields of about 2T. Differences in thermal contraction between the coil former, conductor constituents, impregnation resin, bandage and heat-sink materials (assembled at room temperature) cause mechanical stresses at operating temperature. Rotating-machine operation adds Lorentz forces and challenging centripetal accelerations up to thousands of g. Second generation-HTS conductors withstand large tensile stresses in axial direction and compression in normal direction. However, shear stresses, axial compression, and tension normal to the conductor can cause degradation in superconducting properties. Such stresses can be mitigated by correct choice of materials, coil lay-out and manufacturing process. A certain stress level will remain, which the conductor must withstand. We have manufactured many impregnated round and race-track coils, using different 2G-HTS conductors, and tested them at temperatures from 25 K to 77 K. Degradation of the superconductor in early coils was traced to the mentioned differences in thermal contraction, and was completely avoided in coils produced later. We will discuss appropriate coil-winding techniques to assure robust and reliable superconductor performance.

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

We report on design, construction and testing of a heavy load HTS bearing for a 4 MVA HTS generator. According to the requirement profile of Siemens the bearing was designed for a shaft weight of 1000 kg. To meet these specifications, Nexans has designed and manufactured a HTS bearing fully encapsulated in a stainless steal cryostat with an operation temperature of −240 °C. The working elements of the bearing are single-domain YBCO monoliths fabricated by a top-seeded-melt-growth process, optimized for large batches with 64 pieces per batch. The monoliths exhibit trapped magnetic fields up to 1.4 T and self-field critical current densities at 77 K up to 1.3 × 105 Acm−2. The stator of the bearing comprises 270 such monoliths, which were arranged in nine rings. The levitation properties of the complete system, comprising the HTS stator and a permanent magnet rotor, were recently successfully tested. The system is the largest bearing manufactured worldwide and one of the first to be tested for industrial applications.

HTS magnetic bearings are inherently stable without an active feedback system. They provide low frictional losses, no wear and allow operation at high rotational speed without lubrication. So they are very promising for use in motors, generators and turbines. We designed and constructed an HTS radial bearing for use with a 400 kW HTS motor. It consists of alternating axially magnetized permanent magnet rings on the rotor and a segmented YBCO stator. Stator cooling is performed by liquid nitrogen, the temperature of the stator can be adjusted by varying the pressure in the cryogenic vessel. At 68 K maximum radial forces of more than 3.7 kN were found. These results range within the highest radial bearing capacities reported worldwide. The encouraging results lead us to develop a large heavy load HTS radial bearing. Currently a high magnetic gradient HTS bearing for a 4 MVA synchronous HTS generator is under construction.

Optimized design of synchronous machines can be achieved by use of HTS tape conductors. The introduction of an iron-free air-core stator winding and replacement of the rotor’s copper windings by Bi-2223 tapes allows to develop very compact HTS machines with less than half the weight and volume, higher efficiency and excellent operational behavior compared to conventional devices. In consequence these rotating machines with HTS rotors become very attractive for ship drives, power generation and industrial applications. A 400 kW synchronous HTS machine was designed, manufactured and tested at Siemens. Main goal was to demonstrate the feasibility of basic concepts. Development of a 4 MVA synchronous HTS generator is currently under way.

Promising results of static and dynamic investigations on various journal type test bearings encouraged us to develop a scaled-up HTS bearing, able to carry the HTS rotor of a 400 kW superconducting motor. The stator, a YBCO hollow cylinder of 203 mm inner diameter and 250 mm length, is cooled by liquid nitrogen. Permanent magnet rings with a diameter of 200 mm were mounted on a shaft with alternating polarity. Characterization of the bearing capacity was performed with three different YBCO stators at temperatures between 66 and 86 K in a test set-up. A significant influence of the temperature was found. At a stator temperature of 72 K and a rotation frequency of 25 Hz (corresponding to nominal motor speed) a radial bearing force of 2700 N was measured for the shaft at centre position. Under rotation of the shaft the bearing capacity is reduced. At present our results range within the highest radial bearing capacities reported world-wide.

We have tested a heavy load HTS radial bearing dedicated for use in motors, generators, and flywheels. The HTS bearing is of radial type design providing both radial and axial support. The stator and rotor are modular assemblies which allows up-scaling in size. The superconducting stator is made of polycrystalline melt-textured (pmt) YBCO 200 mm inner diameter hollow cylinder grown in cylinder-like a-b texture. The stator assembly is composed of axially stacked YBCO rings in a Cu tube and cooled from the outside by LN/sub 2/. The rotor consists of stacked annular PM rings in compression on a shaft. This results in a high radial magnetic field gradient. Three such YBCO stators have been fabricated, assembled, and tested for use with a 380 kW superconducting motor developed by SIEMENS. Maximum radial forces of more than 3.7 kN were measured (at a temperature of 68 K) with the shaft at center radial position. The goal is to demonstrate safe operation of heavy rotors in a desired frequency range by providing sufficient forces, stiffness, and damping at critical modes.

The interaction between high temperature superconductors (HTS) and permanent magnets allows to realize an inherently stable contactless bearing without active feedback system. It has no wear, very low friction and allows operation at high rotational speed. Its thermal inertia prevents a sudden breakdown. High magnetic gradient bearings with a special magnet configuration work both radially and axially. We have designed and constructed a test set-up with two HTS journal type bearings. Investigation of characteristic bearing features was performed in quasi-static experiments with different YBCO stators. Stiffness of the bearings and the dependence of losses per force–displacement cycle on the amplitude were characterized. Losses per force–displacement cycle were investigated in dynamic measurements with frequencies between 0.01 and 40 Hz and resulted in nearly frequency independent behaviour.

The aim of this work is to develop a function model of a resistive HTSC fault current limiter. The switching elements of the fault current limiter are bath-cooled in a liquid nitrogen cryostat. The elements consist of YBaCuO films which are deposited on different substrates with critical current densities of up to 3/spl middot/10/sup 6/ A/cm/sup 2/. For the most effective limiting samples so far the peak let-through current was twice tile nominal current and the steady short-circuit current below nominal current. The concept of a 100 kVA function model is introduced.

Since the discovery of superconductivity above liquid nitrogen temperature in copper oxide based compounds many experiments have been performed on the one hand to study their mixed state properties and on the other hand to check their technological applicability. Due to their well defined cylindrical shape latent particle tracks (also known as columnar defects) are a powerful tool to investigate the mixed state in high temperature superconductors (HTSC) as they provide optimized pinning centers. Therefore in this paper we will present experiments performed with HTSC samples (epitaxial thin films on SrTiO 3 substrates, single crystals and technical tapes) containing columnar defects. We will outline the influence of these linear defects on the resistive phase transition and on transport I–V curves of YBa 2 Cu 3 O 7−δ (123) thin films. All HTSC known up to now exhibit a pronounced structure-related anisotropy. Hence we present magnetic and transport measurements concerning the angular dependence of the critical current in various irradiated HTSC compounds. Furthermore experiments with technical tapes of (BiPb) 2 Sr 2 Ca 2 Cu 3 O 10 (Bi2223) will be shown giving an overview of problems concerning technological applications. Finally in irradiated and nonirradiated Bi 2 Sr 2 CaCu 2 O 8 (Bi2212) single crystals the flux line lattice is visualized via the high resolution Bitter decoration technique.

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.

We investigated the voltage-current (V-I) characteristics in polycrystalline, melt textured and epitaxially grown Bi-2212 superconductors, in Bi-2223 melt textured Ag tapes and in Y-123 films. In all samples the V-I curves are well described by a power law behaviour V ∝ I P over many orders of magnitude in the voltage V. With increasing magnetic field and temperature the exponent p decreases with 1/B from a maximum at p=10–20 down to the ohmic limit p=1. In a double logarithmic plot the V-I lines extrapolate to a common hinge point. These results are interpreted within the frame of thermally activated flux creep. From the measurements on thin films and bulk of Bi 2 Sr 2 CaCu 2 O x we derive an expression for an effective activation energy U eff (B,T,j)=60 meV/B (1-T/T c ) 5/2 ln j o /j. We show that a number of experimental observations are in accordance with this explicit result. In particular (a) exponential decay of the critical current density with field, (b) nonlogarithmic flux creep and (c) the irreversibility field B irr (T) emerge as consequences of the specific functional dependence of U eff .

A comparative study of transport and magnetic properties was made for epitaxial YBa2Cu3O7−δ thin films. Good correspondence was found for the current-voltage characteristics determined by transport and magnetic measurements. This fact gives direct evidence for the validity of the Bean model in the case of thin films. Different types of E(J) relations were analysed. The best agreement was found for the current-voltage characteristics with the vortex activation energy dependence U(J) = UO(JO/J)μ. The temperature dependences of the parameter μ are obtained for different magnetic fields.

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.

The critical current density jc(B,T, Theta ) of epitaxial YBa2Cu3O7-Gd and Bi2Sr2CaCu2O8+x films has been measured in detail. In the 2D regime, jc( Theta ) depends only on the field component B//c for both materials. An improved jc( Theta ) model for YBa2Cu3O7- delta accounts for isotropic pinning centers in the 3D regime.

High-temperature superconducting (HTS) transformers are very promising candidates for application in electrical power engineering. Their main advantages are reduced size, weight, better efficiency and reduced potential fire and environmental hazards. We have designed, constructed and tested a 100 kVA HTS power transformer operated at 77 K. The nominal primary and secondary currents (voltages) are 18 A (5.6 kV) and 92 A (1.1 kV), respectively. No-load tests, short-circuit tests and load tests proved repeatedly that the transformer has the rated capacity. HTS winding losses of 20.6 W and iron losses of 403 W were measured.

The presently available high temperature superconducting materials (HTS) transport electric current at high current densities with negligible electric losses. This makes it possible to create higher magnetic fields. Using these features in a rotating electric machine it is possible to reduce the over-all dimensions and weight of the machine, to increase the efficiency and to improve additional features of the machine. To address these goals Siemens started three R&D projects to develop, manufacture and test electric machines with high temperature superconducting field windings. A 400 RW synchronous motor was followed up by a 4000 kVA high speed generator. A 4000 kW high-torque motor will be the third step. Additional to the application in electric machines it is possible to use the substantial advantages of high temperature superconducting materials for passive magnetic bearings. These are operating without any control device of the magnetic field. Siemens started the development of heavy load HTS bearings in parallel to the development of HTS machines

In an increasing number of electric power grids the share of distributed energy generation is also increasing. The grids have to cope with a considerable change of power flow, which has an impact on the optimum topology of the grids and sub-grids (high-voltage, medium-voltage and low-voltage sub-grids) and the size of quasi-autonomous grid sections. Furthermore the stability of grids is influenced by its size. Thus special benefits of HTS applications in the power grid might become most visible in confined power grids.

High-energy (2.7GeV) Au-ions produce columnar tracks in the order of 10nm in diameter, which act as most effective pinning centers. The goal of our irradiation experiments is twofold: firstly, to explore the possible enhancement of critical transport current in the 2223 BPSCCO Ag-tapes currently used as promising conductor material and secondly, to investigate the basic flux pinning mechanism and possible granularity in the samples. The 2223 BPSCCO Ag-tapes were made by the powder in tube technique and irradiated up to doses of 3.5x1011 Au -ions/cm2 at a temperature of 100K. The samples were characterised both by transport jct and magnetization measurements up to 13T and at temperatures ranging from 4.2K to 100K. Granularity of samples was investigated by voltage-current curves. At 77K the irreversibility field derived from jcm could be enhanced by a factor five for orientation Bile. The irreversible magnetization of samples irradiated at an angle of 30° shows a maximum when the field is aligned parallel to the line defects. This behaviour points to the fact that the 2D-pancake vortices are not completely decoupled. The irradiation induced effects will be compared with those obtained on 2212 BSCCO melt textured layers on Ag tape and for different projectiles.

A low-speed high-torque HTS machine is being developed at Siemens on the basis of previous steps (400kW demonstrator, 4MVA generator). The goal of the programme is to utilize the characteristic advantages offered by electrical machines with HTS-excited rotor, such as efficiency, compact size, and dynamic performance. To be able to address future markets, requirements from ship classification as well as potential customers have to be met. Electromagnetic design cannot be focused on nominal operation only, but has to deal with failure modes like short circuit too. Utilization of superconductor requires to consider margins taking into account that the windings have to operate reliably not only in "clean" laboratory conditions, but in rough environment with the stator connected to a power converter. Extensive quality control is needed to ensure homogenous performance (current capacity, electrical insulation, dimensions) for the large quantity of HTS (45 km). The next step was to set up and operate a small-scale "industrial" manufacturing process to produce HTS windings in a reproducible way, including tests at operating conditions. A HTS rotor includes many more components compared to a conventional one, so tough geometric tolerances must be met to ensure robust performance of the system. All this gives a challenging task, which will be concluded by cold testing of the rotor in a test facility. Then the rotor will be delivered for assembly to the stator. In following machine tests the performance of the innovative HTS drive system will be demonstrated.