J M Ceballos

Universidad de Extremadura, Cáceres, Extremadura, Spain

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Publications (17)17.03 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: The sand pile model, in conjunction with Bean model, is often applied to describe single grain bulk superconductors. However, in several applications such as electric motors, multiseeded bulks are needed, due to the need to increase sample dimensions. In this paper, an extension of the sand pile model is presented in order to manage this type of materials. Multiseeded HTS bulk superconductors, produced, e.g., by the top-seeded melt growth process, are characterized by intra- and intergrain currents, and these are reflected in the model. However, identifying these currents from flux density measurements is not straightforward, when considering more than one grain. In fact, the number of currents increases with the number of grains, and these have to be identified from the measured field surface. A method to identify these currents based on genetic algorithms is validated with artificial data and then used in real measurements.
    IEEE Transactions on Applied Superconductivity 06/2013; 23:8000804 - 8000804. · 1.20 Impact Factor
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    ABSTRACT: Superconducting magnetic energy storage (SMES) is characterized by low-energy density but high-power density, making this an unfeasible approach for bulk energy storage. Nevertheless, there are applications where high amounts of power must be available for a short period of time, like power quality applications. The core element of SMES is the superconducting coil. Different approaches are found in the literature considering the modeling of this component, either for design or simulation purposes. These usually consist of analytical or numerical approaches. The former allows fast results, but only considers geometric effects. The latter provides accurate results, considering, besides electromagnetic, also mechanical and thermal effects. In this paper, a review of these models is performed, and analytical models are used in an algorithm that allows optimizing equivalent inductance for a specified length of tape. Two small prototypes are fabricated, and experimental measurements carried out, in order to validate the models that are in the base of the proposed algorithm.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):4900104-4900104. · 1.20 Impact Factor
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    ABSTRACT: High temperature superconducting (HTS) machines are recognized to offer several advantageous features when comparing to conventional ones. Amongst these, highlights the decrease in weight and volume of the machines, due to increased current density in conductors or the absence of iron slots' teeth; or the decrease in AC losses and consequent higher efficiency of the machines, even accounting for cryogenics. These concepts have been already demonstrated and some machines have even achieved commercial stage. In this paper, several alternative approaches are applied to electrical motors employing HTS materials. The first one is an all superconducting linear motor, where copper conductors and permanent magnets are replaced by Bi-2223 windings and trapped flux magnets, taking advantage of stable levitation due to flux pinning, higher current densities and higher excitation field. The second is an induction disk motor with Bi-2223 armature, where iron, ironless and hybrid approaches are compared. Finally, an innovative command strategy, consisting of an electronically variable pole pairs' number approach, is applied to a superconducting hysteresis disk motor. All these concepts are being investigated and simulation and experimental results are presented.
    IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
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    ABSTRACT: Superconducting fault current limiters (SFCL) use the transition of superconducting materials as the mechanism to introduce high impedance in the line to be protected when the current in the line surpasses the fixed maximum value. When the normal working current passes through the line, the device exhibits almost zero impedance. The transition of the supercon- ductor may be due to the current crossing the material or the magnetic field surrounding the material. In order to evaluate the possibilities of externally shunted non-stabilized YBCO tape for the design of resistive SFCL with transition by current and magnetic field, a study of this tape was made. First, the AC loss was determined as a function of the value of the transport current. This permits us to know what cooling power is required in the normal state and the value of the critical current that makes the material transit. Second, we studied the tape stabilized by external resistances, to get information about the behavior of the tape carrying current greater than the critical current. Finally, the variation of the critical current and AC loss in the presence of magnetic fields was studied. Some comments about the relation between all these parameters and the possibility of designing SFCL using this tape are included as conclusions.
    IEEE Transactions on Applied Superconductivity 01/2011; 21(3):1267-1270. · 1.20 Impact Factor
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    P. Suárez, A. Álvarez, J.M. Ceballos, B. Pérez
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    ABSTRACT: Most second-generation high-temperature superconductor tapes are prepared on ferromagnetic substrates. It is known that the presence of this substrate increases the tape's ac losses. Thus, it is important to determine the contribution of the ferromagnetic loss to adequately evaluate the ac loss and achieve good designs of superconducting power devices based on YBCO-coated conductors. We here describe the design and testing of an experimental method to determine the ferromagnetic loss in the substrate. The setup consists of two coils wound around a core made of a YBCO tape. One of the coils is a feed coil used to create an alternating magnetic field in the core. The other is a pickup coil used to measure the electromotive force (emf) due to the magnetic field. The core consists of three turns of RABiTS-processed YBCO-coated conductor with nickel alloy substrate and stainless steel stabilization. The values of B and H to obtain the hysteresis cycle were obtained as follows: H was obtained from the current in the feed coil, and B was obtained by integration of the emf measured in the pickup coil. The ferromagnetic loss was measured with different currents, as well as frequencies in the range of 50-100 Hz.
    IEEE Transactions on Applied Superconductivity 11/2010; · 1.20 Impact Factor
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    P. Suarez, A. Alvarez, J.M. Ceballos, B. Perez
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    ABSTRACT: In multilayer and magnetically coupled coils made from tape, the loss in each segment of tape in a coil depends on the parallel segments in the adjacent layers. In the case of a single multilayer coil, the current in all the layers is the same, but in magnetically coupled coils, the current in adjacent layer from different coils can be different both in amplitude and phase-usually 180<sup>deg</sup> out of phase one with respect to the other. In previous work, we have studied the influence of the proximity between tapes by considering the total loss in a segment as the sum of three components: the transport current in it, the global magnetic field due to the complete coil (or coils), and the local magnetic field due to the current in the tape wound just over or under the segment in question. To measure the last component, an experimental method has been proposed and carried out with Bi-2223 tape, showing that the loss in the tape can be increased or reduced by the proximity of another tape, depending on the current, if any, that the latter carries. By means of the loss variation, we have shown how the variation of transport currents (and, therefore, of the associated magnetic fields) influences the practical critical current of the tape under test. Advances in YBCO tape (2G tape) fabrication have led to increases in the field tolerance of the tape, and the dependences of loss and practical critical current on the proximity of an adjacent tape needed to be revised. In the present work, we study the behavior of the loss in 2G tapes under the influence of other tapes carrying zero or different currents. A comparison between Bi-2223 and YBCO tapes is shown.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    A. Alvarez, P. Suarez, B. Perez, J.-M. Ceballos
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    ABSTRACT: The design of a bipolar single-turn coil made of a YBCO bulk was proposed by the group of electrical application of superconductors, at the University of Extremadura, to be an element for the design of a modular low-power two-phase axial-flux motor. The magnetic field is created by several of these elements strategically located in an arrangement that makes the field rotate in the space where a disk-shaped rotor made of YBCO is going to work. Part of the rotor pulling mechanism is due to the trapped magnetic field in the rotating disk and another part is due to the variation of the magnetic field on the surface of the disk, and how the magnetic field is screened by the disk. In this work we study the magnetic field in the space where the rotor works, before and after its placement, and measure the trapped magnetic field in the disk. We present the magnetic field maps obtained on planes located in both sides of the disk, and propose a distribution of the magnetic field lines that justify the measurements and show the screening effect of the disk.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    ABSTRACT: In the field of the application of HTS in electrical motors, most prototypes are made using superconducting coils based on tape and located in the position where copper coils work in a similar conventional motor. Other prototypes use superconducting bulks (usually disk-shaped) in those positions where normal magnets should work in similar conventional motors. But it is very unusual to find designs using electrical coils based on bulks. This is a challenge whose main problem is the difficulty in machining the superconductor bulks to get the proper shape because of the impossibility of bending the material to wind coils. The design of a bipolar single-turn coil made from a superconducting YBCO disk was proposed by the group of Electrical Application of Superconductors, at the University of Extremadura, several years ago to be an element for the design of a modular two-phase inductor for an air core axial-flux motor. The shape of each coil looks like an 'S'. When a current flows through the circuit, two opposite magnetic fields appear in the upper and lower halves of the piece. Until now, attempts to get a good superconducting circuit by cutting a YBCO disk into the required shape have failed because of cracks appearing in the crystal during the process. Last year, our group at the University of Extremadura began to work with ATZ GmbH who have improved the machining process and made the coils. In this paper we present the coil and the first tests carried out.
    Journal of Physics Conference Series 03/2008; 97(1):012180.
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    P Suárez, A Alvarez, B Pérez, J M Ceballos
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    ABSTRACT: Many references on AC losses can be found for straight superconducting tapes with or without an external magnetic field. There are fewer references on AC losses for bent tapes such as we find it in a spire or solenoid. But even fewer are the references on the study of AC losses in multilayer coils or magnetically coupled coils wound close together. In these cases, the loss in each piece of tape depends on three factors: the transport current in it, the global magnetic field due to the complete coil, and the local magnetic field due to the current in the tape wound just over or under the piece in question –the main difference between multilayer coils and magnetically coupled coils is that the current in the former is the same in all the layers and the currents in magnetically coupled coils are different in amplitude and phase. In order to determine the losses due to the third factor above, the local magnetic fields, we propose in this paper an experiment that consists of the measurement of losses in two straight insulated superconducting tapes located one over the other as close together as possible. In this way, the effect of the global magnetic field of the coil disappears because the coil does not exist. Furthermore, one of the tapes is made to be twice as long as the other so that we can measure the part of the transport losses in the part of the tape independent on the influence of the other. This permits us to distinguish the component of the losses due to the interaction between the pair of tapes. BSCCO tape was used and the pieces were fed with two different power supplies each one giving a current adjustable in amplitude. Measurements of the voltages between taps and in contact-less loops were taken both between the tapes and, in the longer tape, away from the influence of the shorter one. The losses were calculated from the wave forms of the contact and contact-less voltages and the currents. The influence of the proximity of the tapes was determined.
    Journal of Physics Conference Series 01/2008; 97(1).
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    E. Pardo, F. Gömöry, J. Šouc, J. M. Ceballos
    Superconductor Science and Technology 04/2007; 20:351. · 2.76 Impact Factor
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    ABSTRACT: Investigation of AC loss under simultaneous action of transport AC and external AC field is of prime importance for reliable prediction of dissipation in electric power devices like motors/generators, transformers and transmission cables. The experimental rig allowing to perform AC loss measurement in such conditions on short (10 cm) samples of tapes from hightemperature superconductor Bi-2223/Ag has been designed and tested. Both the electrical and thermal method have been incorporated, allowing to combine better sensitivity of former one and a higher reliability of the latter one. Our main aim is to see how the AC loss depends on the phase shift between the current and the field. Such a shift could acquire rather different values in various applications. While in transformer winding, the maximum phase shift at full load will probably not exceed a few degrees, in a three phases transmission cable in tri-axial configuration it is around 120°. Therefore we explored the whole range of phase shifts from 0 to 360°. Surprisingly, the maxima of dissipation do not coincide with zero shift as expected from qualitative considerations.
    Journal of Physics Conference Series 07/2006; 43(1):63.
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    ABSTRACT: Investigation of ac loss under the simultaneous action of the transport ac current and the external ac magnetic field is of prime importance for the reliable prediction of dissipation in electric power devices such as motors/generators, transformers and transmission cables. An experimental rig allowing us to perform ac loss measurements in such conditions, on short (10 cm) tape samples of high-temperature superconductor Bi-2223/Ag, was designed and tested. Both the electromagnetic and thermal methods were incorporated, allowing us to combine the better sensitivity of the former and the higher reliability of the latter. Our main aim was to see how the ac loss depends on the phase shift between the transport current and the external magnetic field. Such a shift could have different values in various applications. While in a transformer winding, the maximum phase shift at full load will probably not exceed a few degrees, in a three phase transmission cable in tri-axial configuration it is around 120°. Therefore, we explored the whole range of phase shifts from 0 to 360°. Surprisingly, the maxima of dissipation did not coincide with zero shift as expected from qualitative considerations.
    Superconductor Science and Technology 03/2006; 19(4):397. · 2.76 Impact Factor
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    ABSTRACT: The losses in an HTS tape depend strongly on the perpendicular magnetic field. In order to avoid this magnetic field component in an air core transformer, a toroidal geometry was proposed and studied in previous work. Due to the difficulties that one finds in constructing toroidal coils, the straight solenoidal geometry is now under study. In this case, the magnetic field close to the ends of the coil is not parallel to the axis and a perpendicular component appears. In the present work, the losses due to this component are studied as a function of the coil geometry-i.e., the ratio between length and diameter-and a practical formulation is found.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
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    ABSTRACT: In order to study the viability of coreless AC coupled coils, a superconductor transformer based on BSCCO-2223 PIT tapes was constructed. To achieve the minimum flux leakage, a toroidal geometry was selected. Both secondary and primary coils were wound around a glass fiber reinforced epoxy torus, obtaining a solid system. The field inside the transformer, the coupling factor, and the losses in the system were computed and measured, providing suitable parameters for new improvements in these systems.
    IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor
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    ABSTRACT: Most work on bulk-based superconducting electrical motors has been done with superconducting materials in the rotor only, due to the difficulty in machining the material into the conventional coil shape. As part of the design of a superconducting induction motor with superconductors in both rotor and stator, we made a disk-shaped rotor from the same YBCO bulks that we use to fabricate ceramic coils in constructing a modular stator for a biphasic axial flux motor, and studied this rotorÕs working behaviour. To this end we constructed a system to simulate the working en-vironment of a YBCO disk within the motor, and measured the magnetic field in the disk and the speed–torque characteristic.
    Physica C Superconductivity 01/2003; 398(3). · 0.72 Impact Factor
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    ABSTRACT: As part of the design of a superconducting induction motor with axial flux, the dynamic behaviour was studied of a superconducting, disk-shaped rotor located in an axial, bipolar, rotating magnetic field.When the disk was rotating due to the field, different external torques were applied to its shaft, and the torque and speed were measured.This work presents the results of these measurements and a model explaining the observations.

Publication Stats

37 Citations
83 Downloads
944 Views
17.03 Total Impact Points

Institutions

  • 2005–2008
    • Universidad de Extremadura
      • • Escuela de Ingenierías Industriales
      • • Departamento de Ingeniería Eléctrica, Electrónica y Automática
      Cáceres, Extremadura, Spain
  • 2007
    • Slovak Academy of Sciences
      • Institute of Electrical Engineering
      Presburg, Bratislavský, Slovakia