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J. Rieger

Bio: J. Rieger is an academic researcher from Siemens. The author has contributed to research in topics: Magnetization & Magnetic field. The author has an hindex of 11, co-authored 30 publications receiving 451 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the dynamic resistance in a slab-like superconductor is calculated, taking into account a field-dependent critical current density, and the model predicts the observed dependence of dynamic resistance on field amplitude, field frequency and transport current.
Abstract: The dynamic resistance in a slab-like superconductor is calculated, taking into account a field-dependent critical current density. In superconductors carrying DC transport current in an AC external magnetic field, the dynamic resistance causes a transport loss which depends on the amplitude and frequency of this field as well as on the transport current. This resistance is calculated analytically in a critical-state model applied to a superconducting slab in a parallel field. The field has a general periodic time dependence and for the superconductor a relation between critical current and momentary magnetic field as in the Kim model is assumed. The dynamic resistance appears only at field amplitudes larger than the so-called threshold field, which depends on the transport current. The model predictions are compared with experimental results obtained with a Bi-2223/Ag tape at liquid-nitrogen temperature. At small field amplitude and at low transport current, the derived model predicts the observed dependence of dynamic resistance on field amplitude, field frequency and transport current. For a larger field amplitude and simultaneous high transport current, the resistance is found to be larger than the model predicts. This is probably due to the not completely slab-like geometry and/or to a different field dependence of the critical current density in a high AC field.

118 citations

Journal ArticleDOI
TL;DR: In this article, the authors summarized world-wide efforts in the development of superconducting transformers and reports on the progress achieved at Siemens, where they developed a 1-MVA demonstrator transformer for laboratory testing, exhibiting innovative features like horizontal design, cabled-conductor windings and closed cooling cycle with sub-cooled nitrogen.
Abstract: 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.

45 citations

Journal ArticleDOI
TL;DR: In this article, the energy loss in multifilamentary superconducting tapes has been measured for various orientations of the external ac magnetic field, and the loss at intermediate field angles can be predicted over a wide range of field amplitudes based on the following assumptions: for low-field amplitudes, the current patterns that would be induced in the tape by the parallel and perpendicular field components can be summed.
Abstract: The energy loss in multifilamentary superconducting tapes has been measured for various orientations of the external ac magnetic field. When the ac loss in parallel and perpendicular fields is known, the loss at intermediate field angles can be predicted over a wide range of field amplitudes. The prediction is based upon the following assumptions: For low-field amplitudes, the current patterns that would be induced in the tape by the parallel and perpendicular field components can be summed. For high-field amplitudes, the tape only carries the current pattern induced by the perpendicular field component. These assumptions are supported by theory.

41 citations

Journal ArticleDOI
TL;DR: In this article, a high-temperature superconducting (HTS) 110 kV/400 MVA cable for future power transmission systems in densely populated areas is presented, which consists of coaxial conductors made of 2223 BPSCCO multifilament tapes, a LN2-high-voltage insulation, a flexible cryostat, terminations and a cooling system.
Abstract: 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.

39 citations

Journal ArticleDOI
TL;DR: In this paper, the ac loss in high-Tc superconducting tapes with twisted and non-twisted filaments has been studied by a magnetic method and measurements were made at 77 K in a magnetic field of 50 Hz frequency and 0.001-0.7 T amplitude.
Abstract: The ac loss in high-Tc superconducting tapes with twisted and non-twisted filaments has been studied by a magnetic method. A brief overview of the theoretical background and the experimental set-up is presented. Measurements were made at 77 K in a magnetic field of 50 Hz frequency and 0.001-0.7 T amplitude. Application of dc transport current made it possible to distinguish between the loss components, arising from intra-grain and from filament currents. The magnitude of the filament loss component indicates that the filaments are fully coupled, which agrees with theory. In other measurements, the orientation of the external field with respect to the tape was varied. Knowledge of the ac loss in parallel and in perpendicular field is sufficient to predict the ac loss for any intermediate orientations of the field.

38 citations


Cited by
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Journal ArticleDOI
TL;DR: This paper presents a literature review of the methods for computing ac losses in HTS tapes, wires, and devices and provides an estimation of the losses occurring in a variety of power applications.
Abstract: Numerical modeling of superconductors is widely recognized as a powerful tool for interpreting experimental results, understanding physical mechanisms, and predicting the performance of high-temperature-superconductor (HTS) tapes, wires, and devices. This is particularly true for ac loss calculation since a sufficiently low ac loss value is imperative to make these materials attractive for commercialization. In recent years, a large variety of numerical models, which are based on different techniques and implementations, has been proposed by researchers around the world, with the purpose of being able to estimate ac losses in HTSs quickly and accurately. This paper presents a literature review of the methods for computing ac losses in HTS tapes, wires, and devices. Technical superconductors have a relatively complex geometry (filaments, which might be twisted or transposed, or layers) and consist of different materials. As a result, different loss contributions exist. In this paper, we describe the ways of computing such loss contributions, which include hysteresis losses, eddy-current losses, coupling losses, and losses in ferromagnetic materials. We also provide an estimation of the losses occurring in a variety of power applications.

290 citations

Journal ArticleDOI
TL;DR: HTS Roebel cables from REBCO coated conductors were first manufactured at the Karlsruhe Institute of Technology and have been successively developed in a number of varieties that provide all the required technical features such as fully transposed strands, high transport currents and low AC losses, yet retaining enough flexibility for a specific cable design.
Abstract: Energy applications employing high-temperature superconductors (HTS), such as motors/generators, transformers, transmission lines and fault current limiters, are usually operated in the alternate current (AC) regime. In order to be efficient, the HTS devices need to have a sufficiently low value of AC loss, in addition to the necessary current-carrying capacity. Most applications are operated with currents beyond the current capacity of single conductors and consequently require cabled conductor solutions with much higher current carrying capacity, from a few kA to up to 20-30 kA for large hydro-generators. A century ago, in 1914, Ludwig Roebel invented a low-loss cable design for copper cables, which was successively named after him. The main idea behind Roebel cables is to separate the current in different strands and to provide a full transposition of the strands along the cable direction. Nowadays, these cables are commonly used in the stator of large generators. Based on the same design concept of their conventional material counterparts, HTS Roebel cables from REBCO coated conductors were first manufactured at the Karlsruhe Institute of Technology (KIT) and have been successively developed in a number of varieties that provide all the required technical features such as fully transposed strands, high transport currents and low AC losses, yet retaining enough flexibility for a specific cable design. In the past few years a large number of scientific papers have been published on the concept, manufacturing and characterization of such cables. Times are therefore mature for a review of those results. The goal is to provide an overview and a succinct and easy-to-consult guide for users, developers, and manufacturers of this kind of HTS cables.

202 citations

Journal ArticleDOI
TL;DR: In this article, the authors provide an overview and a succinct and easy-to-consult guide for users, developers, and manufacturers of high-temperature superconductors (HTS) cable.
Abstract: Energy applications employing high-temperature superconductors (HTS), such as motors/generators, transformers, transmission lines and fault current limiters, are usually operated in the alternate current (ac) regime. In order to be efficient, the HTS devices need to have a sufficiently low value of ac loss, in addition to the necessary current-carrying capacity. Most applications are operated with currents beyond the current capacity of single conductors and consequently require cabled conductor solutions with much higher current carrying capacity, from a few kA up to 20–30 kA for large hydro-generators. A century ago, in 1914, Ludwig Roebel invented a low-loss cable design for copper cables, which was successively named after him. The main idea behind Roebel cables is to separate the current in different strands and to provide a full transposition of the strands along the cable direction. Nowadays, these cables are commonly used in the stator of large generators. Based on the same design concept of their conventional material counterparts, HTS Roebel cables from REBCO coated conductors were first manufactured at the Karlsruhe Institute of Technology and have been successively developed in a number of varieties that provide all the required technical features such as fully transposed strands, high transport currents and low ac losses, yet retaining enough flexibility for a specific cable design. In the past few years a large number of scientific papers have been published on the concept, manufacturing and characterization of such cables. Therefore it is timely for a review of those results. The goal is to provide an overview and a succinct and easy-to-consult guide for users, developers, and manufacturers of this kind of HTS cable.

162 citations

Journal ArticleDOI
TL;DR: In this paper, the standard elasticity theory and methods of measuring the strain of single-crystal semiconductor layers are discussed, and both theoretical and experimental determinations of critical thickness are considered.
Abstract: Single-crystal semiconductor layers can be grown with large coherency strains. This review covers their standard elasticity theory and methods of measuring the strain. High-quality strained layers are thermodynamically stable up to a critical thickness, and both theoretical and experimental determinations of critical thickness are considered. Above critical thickness there is a metastable regime, with thicknesses of a few tens of nanometres for a typical misfit e0∼1%. A relaxation critical thickness is identified, above which compressive strain produces plastic relaxation so the strain in a layer is less than its misfit (tensile layers commonly experience cracking instead of plastic relaxation). Relaxing layers may have a misfit e0∼1%, and thicknesses of a few hundred nanometres. In the high-mismatch regime, any strain severely perturbs the crystal growth; this occurs typically for misfits of 2% upwards. The review concludes with some unresolved questions about multilayer structures.

154 citations

Journal ArticleDOI
TL;DR: In this paper, a 16-strand RACC-cable with 19 cm transposition length made from coated conductors (CC) material from the commercial supplier SuperPower achieved a transport critical current of 77 K (Jeng = 11.3 kAcm-2).
Abstract: RBCO (R = Y or rare earth element) coated conductors (CC) are the most promising HTS materials for future high field coils operated at moderately high temperature (40-50 K). Coils are planned for the second generation of fusion reactors (DEMO, "DEMOnstrator") and beyond. A ROEBEL bar concept for a high current (kA-class) low AC loss cable is the most suitable assembling technique for conductors in magnet windings due to the flat rectangular cross section. The presented RACC-cable technique (RACC=ROEBEL assembled coated conductors) works with pre-shaping of tapes into strands with the ROEBEL specific meander geometry. The usually very good bending properties of the CC support the assembling procedure of the RACC-cable. We report on a 16 strand RACC-cable with 19 cm transposition length made from CC material from the commercial supplier SuperPower which reached 1020 A transport critical current at 77 K (Jeng = 11.3 kAcm-2). The basic properties of the virgin YBCO tapes and the shaped strands like orientation and field dependent transport currents, current homogeneity and bending effects, were investigated and correlated with the measured properties of the RACC-cable. Calculation of the self field effects by means of a model adapted to the specific RACC-cable geometry and in particular taking into account the current distribution in the cable, explained the 30% current reduction in the cable quantitatively.

139 citations