Nuno Amaro

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.

A Fast Algorithm for Initial Design of HTS Coils for SMES Applications

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.

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.

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.

AC Losses and Material Degradation Effects in a Superconducting Tape for SMES Applications

Superconducting Magnetic Energy Storage (SMES) systems are one potential application of superconductivity in electric grids. The main element of such systems is a coil, made from superconducting tape. Although SMES systems work in DC conditions, due to highly dynamic working regimes required for some applications, AC currents can appear in the coil. It is then of utmost importance to verify the magnitude of these AC currents and take into account AC losses generated on the tape in the design phase of such system. To assure a proper operation, it is also necessary to know tape characteristics during the device lifetime, which in normal operation conditions can be of decades. Continuous thermal cycles and mechanical stresses to which the tape is subjected can change its characteristics, changing important quantities like critical current (IC) and n-value. It is then also necessary to evaluate tape degradation due to these conditions. A study of AC losses will be here presented, for a short sample of BSCCO tape. IC and n-value degradation due to consecutive thermal cycles will also be studied.

AC losses in Bi-2223 Single-Pancake Coils From 72 to 1152 Hz—Modeling and Measurements

Studies of ac losses in superconducting materials, particularly in pancake coils, are of great importance for a better understanding of the superconductivity phenomena and its applications in power systems. Due to different technical difficulties, these studies are usually performed considering one of two approaches: considering superconducting coils of few turns and studying ac losses in a large frequency range versus superconducting coils with a large number of turns but measuring ac losses only in low frequencies. In this paper, ac losses are simulated and verified experimentally in a 128 turn Bi-2223 coil in a range of frequencies from 72 Hz till 1152 Hz. Obtained results show a frequency-dependent behavior. Experimental results are compared to those obtained from two different numerical modeling methods: one using commercial software based on finite-element methods and another using a variational method approach. All obtained results agree, validating the simulations and serving as basis for simulations with larger high temperature superconducting coils.

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.

Combined Operation of an Unified Power Quality Conditioner and a Superconducting Magnetic Energy Storage System for Power Quality Improvement

Superconducting Magnetic Energy Storage (SMES) is a class of promising superconducting devices, considering its possible applications in power systems. This paper describes a combination of a SMES with a Unified Power Quality Conditioner (UPQC) for power quality improvement in an electric grid. The SMES device is used to improve the UPQC performance by increasing the stored energy in the DC link. Several power quality faults including voltage sags and current harmonics are simulated and the system behavior is demonstrated. This hybrid system has the advantage of being able to overcome different kinds of power quality faults with higher performance than as a set of individual systems, thus increasing power quality in electric grids.