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  • 1
    Language: English
    In: IEEE transactions on applied superconductivity, 2014-06, Vol.24 (3), p.1-5
    Description: In this contribution, we develop a refined numerical model of pancake coils assembled from a coated conductor Roebel cable, which includes the angular dependence of the critical current density J c on the magnetic field and the actual (three-dimensional) shape of the current lead used to inject the current. Previous works of ours indicate that this latter has an important influence on the measured value of the AC losses. For the simulation of the superconductor, we used two alternative models based on different descriptions of the superconductor's properties and implemented in different mathematical schemes. For the simulation of the current lead we use a full three-dimensional finite-element model. The results of the simulation are compared with measurements and the main issues related to the modeling and the measurement of Roebel coils are discussed in detail.
    Subject(s): Superconducting cables ; numerical simulations ; Power cables ; coils ; Computational modeling ; Roebel cables ; Superconducting magnets ; Loss measurement ; AC losses ; Superconducting coils ; Electrical engineering. Electrical power engineering ; Applied sciences ; Various equipment and components ; Electric connection. Cables. Wiring ; Exact sciences and technology ; Finite element method ; Usage ; Innovations ; Superconductivity
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 2
    Language: English
    In: IEEE transactions on applied superconductivity, 2016-04, Vol.26 (3), p.1-4
    Description: Stacks of high-temperature superconducting tape can be magnetized to produce a variety of different trapped field profiles in addition to the most common conical or pyramidal profiles. Stacks of tape using discarded Roebel cable offcuts were created to investigate various stacking arrangements with the aim of creating a stack that can be magnetized to produce a uniform trapped field for potential applications such as NMR. A new angled stacking arrangement proved to produce the flattest, most uniform field of all the overlapping stacking arrangements and has the potential to be scaled up. FEM modeling in COMSOL was also performed to complement the measurements and explain the limitations and advantages of the stacking arrangements tested.
    Subject(s): Superconducting cables ; tapes ; superconducting tapes ; Magnetic field measurement ; Superconducting films ; stack of HTS ; Hall probe scans ; Stacking ; Superconducting magnets ; Surface roughness ; Rough surfaces ; Roebel cable
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 3
    Language: English
    In: IEEE transactions on applied superconductivity, 2016-04, Vol.26 (3), p.1-6
    Description: BEST PATHS (acronym for "BEyond State-of-the-art Technologies for rePowering Ac corridors and multi-Terminal HVDC Systems") is a collaborative project within the FP7 framework of the European Commission that includes an MgB 2 -based power transmission line among its five constituent demonstrators. Led by Nexans and bringing together transmission operators, industry and research organizations, this demonstrator aims at validating the novel MgB 2 technology for very high power transfer (gigawatt range). The project foresees the development of a monopole cable system operating in helium gas in the range of 5-10 kA/200-320 kV, corresponding to a transmitted power from 1 to 3.2 GW. The main research and demonstration activities that will be pursued over the four-year project duration are: 1) development and manufacturing of MgB 2 wires and of the cable conductor; 2) design and manufacturing of the HVDC electrical insulation of the cable; 3) optimization of the required cryogenic system; 4) electromagnetic field analysis; 5) design and construction of a prototype electrical feeding system, including terminations and connectors; 6) testing of the demonstrator; 7) study of grid connection procedures and integration of a superconducting link into a transmission grid; and finally, 8) a socio-economic analysis of the MgB 2 power transmission system. CIGRE recommendations will be used to take into account the established international practices, and guidance will be given on newly addressed technical aspects. An overview of the project is presented in this paper, including the main tasks and challenges ahead, as well as the partners and their roles.
    Subject(s): Superconducting cables ; Cooling ; HVDC transmission ; Wires ; Cable insulation ; superconducting links ; BEST PATHS ; high-power transmission lines ; MgB2 cables ; HVDC
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 4
    Language: English
    In: IEEE transactions on applied superconductivity, 2014-12, Vol.24 (6), p.1-8
    Description: Striation of high-temperature superconductor coated conductors as a way to reduce their magnetization ac losses has been the subject of intense worldwide research in the past years by several groups. While the principle of this approach is well understood, its practical application on commercial materials to be used in power applications is still far to be implemented due to manufacturing and technological constraints. Recent advances in tape quality and striation technology are now enabling systematic investigations of the influence of the number of filaments on ac loss reduction with a consistency that was not available in the past. In the present work, we demonstrate the technological feasibility of importantly reducing the magnetization losses of commercially available coated conductors by striating them into a high number of filaments (up to 120). The loss reduction exceeds one order of magnitude and does not come at the expense of current-carrying capability: samples with 10 and 20 filaments are unaffected by the striation process, whereas samples with 80 and 120 filaments still retain 80% and 70% of the current-carrying potential, respectively. We also investigate the transverse resistivity between the filaments in order to understand the paths followed by the coupling currents: we found that the coupling current prevalently flows in the metallic substrate, rather than in and out of the filaments. Finally, we use oxidation as a method to reduce the coupling currents and the corresponding losses. The contribution of this work is threefold: 1) it describes the know-how to produce a large number of high-quality striations in commercially available coated conductors, greatly reducing their losses without extensively degrading their transport properties; 2) it provides a comprehensive characterization of the said samples (e.g., measurements in a wide frequency range, transverse resistance profiles, influence of oxidation on dc and ac behavior of the sample); and 3) it provides new insight on the patterns of the coupling currents.
    Subject(s): High-temperature superconductors ; Critical current density (superconductivity) ; Current measurement ; Conductors ; Loss measurement ; Oxidation ; Yttrium barium copper oxide ; Measurement ; Magnetization ; Analysis ; Innovations ; Barium compounds ; Voltage ; High temperature superconductors ; Copper ; Electric properties ; Magnetic properties
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 5
    Language: English
    In: IEEE transactions on applied superconductivity, 2011-06, Vol.21 (3), p.3021-3024
    Description: In the past few years the Roebel technique has been established as a method for cabling of coated conductor tapes to achieve high current carrying capabilities for low ac-loss applications. We have successfully developed Roebel cables consisting of up to 50 tapes and with current carrying capabilities up to 2.6 kA (77 K, self-field). However, for applications like busbars or fusion magnets current carrying capabilities of more than 10 kA are required. Such high current carrying capabilities cannot be reached by a simple scale-up with additional tapes. We present a concept for Coated Conductor Rutherford Cables (CCRCs) for currents exceeding 10 kA using Roebel subcables as strands. The first steps towards a short subsize CCRC demonstrator cable with electrical and mechanical characterization of commercial coated conductor tapes, strands and a first Roebel strand have been performed and will be discussed.
    Subject(s): Current measurement ; Windings ; Mechanical cables ; Superconducting magnets ; Conductors ; Coated conductors ; superconducting cables ; Perpendicular magnetic anisotropy ; mechanical performance ; Electrical engineering. Electrical power engineering ; Applied sciences ; Electromagnets ; Various equipment and components ; Electric connection. Cables. Wiring ; Exact sciences and technology
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 6
    Language: English
    In: IEEE transactions on applied superconductivity, 2013-06, Vol.23 (3), p.5900205-5900205
    Description: Roebel cables are a promising solution for high-current, low ac loss conductors for various applications, including magnets, rotating machines, and transformers, which generally require the cable to be wound in a coil. We recently assembled and characterized a 5 m long sample and wound it into pancake coils. In this contribution, we investigate the ac loss behavior of such pancake coils by means of numerical simulations based on two complementary models: the finite-element model based on the H -formulation and the minimum magnetic energy variation method based on the critical state. These two numerical models take into account the axis-symmetric geometry of the coil and its detailed structure, simulating each strand composing the cable. The local current density and magnetic field distributions are shown and the ac losses for various current amplitudes are computed. The influence of the number of turns and of their separation on the ac losses is investigated. The results of the computations are compared with the measurements and the main reasons for the observed discrepancy are discussed.
    Subject(s): Coils ; numerical simulations ; Power cables ; Computational modeling ; Magnetic separation ; Current measurement ; Roebel cables ; Ac losses ; Loss measurement ; Numerical models ; Transformers and inductors ; Electrical engineering. Electrical power engineering ; Special rotating machines ; Exact sciences and technology ; Applied sciences ; Electromagnets ; Electrical machines ; Various equipment and components
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 7
    Language: English
    In: IEEE transactions on applied superconductivity, 2011-06, Vol.21 (3), p.1209-1212
    Description: A new German government funded project for a resistive fault current limiter has started in September 2009 (ENSYSTROB) and is presented. The consortium includes partners from industry, research centers and utilities. It aims the construction of a 3-phase medium voltage current limiter (12 kV, 800 A) for the protection of the domestic supply in a power plant. A special feature of this application is the presence of large in-rush currents (4100 Ap for 50 ms, 1800 A for 15 s). The superconducting components are bifilar pancake coils consisting of pairs of YBCO-tapes in face to back configuration. Successful limitation experiments on prototype components with prospective currents in the whole range are shown. Also the stability with respect to high voltage could be demonstrated. The AC-losses under normal operation are shown, by simulation and experiment, to be smaller than the heat input of the current leads. The current limiting components are compared with similar elements based on BSCCO 2212 bulk material (Nexans SuperConductors).
    Subject(s): Temperature measurement ; Superconducting films ; Prototypes ; Materials ; AC-losses ; Conductors ; Mathematical model ; coated conductors ; Surges ; fault current limiter ; Electric power plants ; Electrical engineering. Electrical power engineering ; Miscellaneous ; Electrical power engineering ; Exact sciences and technology ; Applied sciences ; Electromagnets ; Connection and protection apparatus ; Various equipment and components ; Electric connection. Cables. Wiring
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 8
    Language: English
    In: IEEE transactions on applied superconductivity, 2011-06, Vol.21 (3), p.3098-3101
    Description: To achieve high currents single HTSC tapes or Roeble strands must be combined into a cable. Many concepts like Rutherford cable, coated cable in conduit or full size cable model of Roebel strands require twisting of the HTSC tapes. Twisting or torsion exerts longitudinal and shear stress on the tapes which degrade the current carrying capabilities. Finite element analysis was done to explain this behavior. However, the influence of longitudinal stress in HTSC tapes on critical current is well documented, but there is no experimental data for pure shear stress available. To verify the finite element analysis shear stress experiments are of significant interest. With a three point bending method shear stress can be applied to a single HTSC tape. Critical current measurements with varying shear stress are conducted for several HTSC tapes. With the experimental results and the longitudinal stress dependence a correlation between torsion experiments and finite element analysis is possible.
    Subject(s): Superconducting films ; Electro-mechanical properties ; Critical current ; shear stress ; Current measurement ; torsion ; high-temperature superconductors ; Steel ; Finite element methods ; Stress ; Stress measurement ; Superconducting devices ; Electrical engineering. Electrical power engineering ; Exact sciences and technology ; Materials ; Electronics ; Applied sciences ; Electromagnets ; Various equipment and components ; Electric connection. Cables. Wiring ; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 9
    Language: English
    In: IEEE transactions on applied superconductivity, 2011-06, Vol.21 (3), p.1311-1314
    Description: Recent progress increasing the critical current density of second generation (2G) high temperature superconductor (HTS) tapes seems also to increase the switching capacity per effective surface area. An optimized (as thin as possible, as thick as necessary) stabilization cap layer allows to maximize the switching capacity of tapes at an acceptable temperature rise and to minimize the overall tape length. We present the architecture of available 2G HTS tapes designed for FCL, address an approximate and a precise HTS model computation under full fault and moderate overload conditions and report on the set of experiments on short tape samples for identifying the optimal stabilized coated conductor according to the required specification of an FCL with large inrush current. As a result we present a tool to optimize the Ag cap layer in dependence on critical current density and limitation time.
    Subject(s): Resistance ; Temperature measurement ; Coated conductor (CC) ; Critical current ; resistive superconducting fault current limiter ; Current measurement ; stabilization ; Conductors ; High temperature superconductors ; 2G YBCO ; Integrated circuit modeling ; Superconducting devices ; Electrical engineering. Electrical power engineering ; Exact sciences and technology ; Materials ; Electronics ; Applied sciences ; Electromagnets ; Connection and protection apparatus ; Various equipment and components ; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 10
    Language: English
    In: IEEE transactions on applied superconductivity, 2015-02, Vol.25 (1), p.1-4
    Description: Roebel cables made of high temperature superconducting (HTS) coated conductors can carry high currents with a compact design and reduced ac losses. Therefore, they are good candidates for manufacturing coils for HTS applications such as motors and generators. In this paper, we present the experimental dc and ac characterization of several coils assembled from a 5-m-long Roebel cable built at Karlsruhe Institute of Technology, which differ in the number of turns and turn-to-turn spacing. Our experiments, which are supported by finite-element-method calculations, show that a more tightly wound Roebel coil, despite having a lower critical (and therefore operating) current, can produce a higher magnetic field than a loosely wound one. For a given magnetic field produced at the coil's center, all the coils have similar ac losses, with the exception of the most loosely wound one, which has much higher losses due to the relatively large current needed to produce the desired field. The experiments presented in this paper are carried out on the geometry of pancake coils made of Roebel cables, but they are exemplary of a more general strategy, based on coupling experiments and numerical simulations, that can be used to optimize the coil design, with respect to different parameters, such as tape quantity, size, or ac loss, the relative importance of which is dictated by the specific application.
    Subject(s): Coils ; Superconducting cables ; Critical current density (superconductivity) ; Power cables ; Conductors ; Loss measurement ; Magnetic fields ; Finite element method ; High temperature superconductors ; Usage ; Numerical analysis ; Innovations
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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