José Maria Ceballos

SUPERCONDUCTING MAGNETIC ENERGY STORAGE - A Technological Contribute to Smart Grid Concept Implementation

The urgent need to solve existing problems in the electric grid led to the emergence of the new Smart Grid (SG) concept. A smart grid is usually described as an electricity network that can intelligently integrate the actions of all players connected to it in order to efficiently deliver sustainable, economic and secure electricity supplies. Smart grids should be flexible, accessible, reliable and economic, bringing great new challenges into grid management. In order to implement this concept it is necessary to consider the operation of several new devices in the electrical grid. A class of these potential devices is Superconducting Magnetic Energy Storage (SMES) that present, among other features, very fast response times. SMES devices can play a key role in helping to overcome several grids’ faults. In this paper it is described the possibility to integrate SMES into SG, and the advantages of this integration.

Contactless Loop Method for Measurement of AC Losses in HTS Coils

Measurements of ac losses in high-temperature superconducting (HTS) coils are of utmost importance for power applications because these are one of the most limiting factors in superconducting devices. There are two possible ways to measure such losses: calorimetric and electromagnetic methods. An electromagnetic method using a contactless loop is reported in this paper. To verify the applicability of such method in medium- to large-sized coils, two different contactless loops were designed and built, and results are compared with those obtained from measurements made with different configurations of voltage taps. All tests were performed at 77 K, using a superconducting coil with a variable number of turns (up to a maximum of 128) wound from BSCCO tape. Currents ranging from zero to the critical value were applied, at frequencies from 72 to 1152 Hz.

Sand Pile Modeling of Multiseeded HTS Bulk Superconductors: Current Densities Identification by Genetic Algorithms

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.

Integration of SMES devices in power systems - opportunities and challenges

Superconducting Magnetic Energy Storage (SMES) systems are one of the superconducting technologies with envisaged applications in power systems. The flexibility of these systems allows a utilization as Energy Storage Systems (ESS) but also as power devices, for power quality applications. In the actual context of electric grids, with the emergence of the paradigm of Smart Grids, the possible applications of SMES systems are discussed, considering the actual state of the art in superconducting materials. Main envisaged applications are presented and a short comparison with other ESS is also performed, as a way to integrate SMES systems into the actual and upcoming context of power systems. Main already running or finished projects using not only standalone SMES systems but also a combination of multiple superconducting devices are also presented. Finally, a short description of concept projects using SMES systems is also given.

Loss and Transition Studies of Shunted Free-Stabilized YBCO Tape for SFCL Applications

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 superconductor 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 rms 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.

Solar potential of rooftops in Cáceres city, Spain

ABSTRACT Climate change is one of the challenges our society has to deal with nowadays. Photovoltaic is one of the main renewable energies and it is gaining ground all around the world. The prediction of solar radiation is crucial for this kind of energy. The aim of this work is to produce a solar potential map of rooftops the city of Cáceres (Spain) providing an overview of the employed methodology. The estimation of global radiation is based on LiDAR data of high density. Historical radiation records have been also employed to define the calculation parameters. The representation of the estimated global radiation on each building provides a wide range of new possibilities in the use of renewable energies and changes the conception of rooftops to a potential source of photovoltaic energy.

Device for Measuring the Thermal Cycling Degradation in 2G Tapes for Electrical Power Applications

The standard electrical engineering applications of high-temperature superconductors (HTSs) as coils (SMESs), motors, power cables, fault current limiters (SFCLs), etc., usually involve operating conditions under which the critical current of HTS tapes might be degraded. The dependence of such magnitude on mechanical properties, frequency variations, or thermal changes is a key concern for the accurate design of those devices. Two of the parameters affecting the critical current when the superconductor operates in broad temperature ranges are the number and the speed of transitions from the superconducting to the normal state. In order to determine how these parameters affect the critical current, we have designed an automated dipping setup in liquid nitrogen to reproduce heating and cooling cycles on superconducting tapes. In this paper, this device is described, and several tests on a short sample of YBCO coated conductor are reported and analyzed.

Validation and Application of Sand Pile Modeling of Multiseeded HTS Bulk Superconductors

Sand pile and Bean models have already been applied to describe single grain HTS bulks. An extension to that approach was used to model multiseed bulks, needed for several practical applications as electric motors or flywheels with superconducting bearings. The use of genetic algorithms was then proposed to determine intra- and intergrain current densities, and application to two and three seeds samples using trapped flux experimental measurements was exemplified. However, this model assumed some simplifications, as equal properties in grain boundaries between neighboring grains. In this paper an extension to this methodology is proposed and evaluated by analyzing measurements performed in plans at different distances from surfaces of samples with three seeds. Discussion of its influence on a practical application is also explored.

Improved Operation of an UPQC by addition of a Superconducting Magnetic Energy Storage system

Power quality is a fundamental concern in modern power grids. Since there is a very broad spectrum of causes for power quality depreciation, it is important to continuously develop devices that can overcome power quality problems in electric grids, thus increasing the quality of energy. Active power filters are one of the main class of devices whose applications are related to power quality improvement. In this paper, a combination of a Unified Power Quality Conditioner and a Superconducting Magnetic Energy Storage system is considered and simulation results indicate that such hybrid system can be used to overcome power quality issues like harmonic distortion, voltage sags/swells and phase unbalance. The advantages of such combination are also discussed and results indicate that the addition of the superconducting device can increase the range of applications of the power active filter.

Experimental Magnetic Field Mapping of a Polycrystalline Superconducting YBCO Disc for an Axial Flux Motor

The method of creating large and complex-shaped melt-textured YBCO bulks based in artificial welding seeds opens the door to the study of applications with polycrystalline superconductor samples. In order to evaluate the superconducting quality of the bulks, Hall probe mapping can be applied in order to measure trapped flux field profiles after magnetisation. This paper describes the magnetic field mapping of an axial flux motor with a polycrystalline high temperature superconductor (YBCO) disc rotor at liquid nitrogen temperature (77 K). An axial flux hall probe is used and magnetic field profiles have been obtained for different polar configurations of a three-phase stator winding which will be operated at 50Hz. After the magnetization of the HTS disc trapped flux is measured, and its magnitude depends on the polar configuration and magnitude of the applied field.