Electric Power Applications Research Articles

Development and Prospects for the Future of Superconducting Wires

Superconducting wires are important from the viewpoints of energy saving and the realization of a low-carbon society, because their applications in various types of electric power applications enable not only improved efficiency but also the reduction of size and weight owing to the fact that they can allow a large electric current density without resistance. Wires of Nb–Ti and Nb3Sn metallic superconductors have conventionally been used in various magnets. The research and development of high-temperature Cu-oxide superconducting wires has been intensively carried out focusing on Bi- and Y-based oxides; recently, the development of long wires of these oxides has also been in progress, and their applications to a variety of power systems are being eagerly discussed. MgB2, whose superconductivity was discovered in Japan in 2001, is also being studied with the aim of fabricating MgB2 wires, and promising performance has been obtained. The research and development of superconducting wires using these materials is expected to achieve further progress and lead to their practical applications in the future.

Design and Application of Var Compensation Method for Traction Power Supply Systems of Electrified Railway

The application of electric power, which acts as a pillar energy and economic artery in modern society, is one of the most important symbols of the level of development and comprehensive national power of a country. Var is a crucial factor for the design and operation of AC power systems, and is closely bound up with the safety, stabilization, and economical operation of power systems. With the development of electrified railway, the importance of the dynamic var compensation for traction power supply systems of electrified railway becomes more and more distinct. Developing the var compensation strategy vigorously has important senses in theory and practice. In this article, synthetically considering technique and economic leval of power systems in our country, parameters modeling and design and verification and specific engineering application of a var compensation method are presented. This method is a preferable one for resolving undesirable effect on power systems from traction power supply systems of electrified railway, especially having dynamic and real time characteristics of var compensation.

Materials Chemistry and the Development of Practical High Temperature Superconductor Wires and Electric Power Applications

not Available.

Will higher Tc superconductors be useful? Fundamental issues from the real world

Abstract

Vehicle Engineering Application Study on TSF Var Compensation Method for Electric Locomotive of Electrified Railway

The application of electric power, which acts as a pillar energy and economic artery in modern society, is one of the most important symbols of the level of development and comprehensive national power of a country. Var is a crucial factor for the design and operation of AC power systems, and is closely bound up with the safety, stabilization, and economical operation of power systems. With the development of electrified railway, developing the var compensation strategy vigorously has important senses in theory and practice. In this article, synthetically considering technique and economic leval of power systems in our country, parameters design and verification and specific engineering application of TSF var compensation method are presented. This method is a preferable one for resolving undesirable effect on power systems of electrified railway, especially having dynamic and real time characteristics of var compensation.

Overview of Materials & Power Applications of Coated Conductors (M-PACC) Project (Japanese National Project)

There are high expectations for coated conductors in electric power applications such as SMES, power cables and transformers owing to their ability to contribute to stabilizing and increasing the capacity of the electric power supply grid, as well as reduce CO2 emissions based on their high critical-current characteristics. R&D has been performed on wires and power devices as part of many national projects all over the world. The Materials & Power Applications of Coated Conductors (M-PACC) project is a national project in Japan supported by the Ministry of Economy, Trade and Indstry (METI) and the New Energy and Industrial Technology Development Organization (NEDO) to develop both coated conductors that meet the market requirements and fundamental technologies for power applications using coated conductors. Three years have passed since this five-year national project started in fiscal 2008. In this article, R&D results are reviewed and compared with the interim/final targets of the project, and the future prospects are discussed.

구리/NaCl 전해질/아연 전기화학전지의 전류특성

The characteristics of electric current for the voltaic cell are important for electric power applications. In this paper, an electrical equivalent model consist of three resisters and a capacitance for the Cu/NaCl solution/Zn electrochemical cell is proposed. The capacitance which exists in the Zn electrode/electrolytic interface increased according to Zn electrode area, but cannot affect almost in electric current. Complex impedance plot was used to analysis the interface effect for Zn/electrolyte. This result shows that the interface is similar with the electric transmission line. The short current measurements were conducted to investigate the effects of hydrogen peroxide, the watery sulfuric acid and NaCl aqueous solution. As the hydrogen peroxide increased, the electric current increased because the hydrogen gas being converted with the water. Also electric current increased significantly with increase of the hydrogen ion with the watery sulfuric acid and increased with increase of Na+ ion and Cl-ion in the NaCl electrolyte.

Thick SmBCO/IBAD-MgO Coated Conductor for High Current Carrying Power Applications

Long-length (Sm1+xB2-xC3O7-y) coated conductor was fabricated using ion beam assisted deposition (IBAD)-MgO template (LaMnO3/IBAD - MgO/Y2O3/Al2O3/Hastelloy) by the reactive co-evaporation method for electric power applications. SmBCO superconducting layers with thicknesses from 1 to 3 ?m were deposited to investigate the effect of SmBCO thickness on the in-plane texture, surface morphology and superconducting properties. In this study, the optimal deposition conditions were examined to make thick SmBCO coated conductor without degradation of critical current density. The oxygen partial pressure and temperature were controlled in the range of 1~20 mTorr and 600 ~ 800°C, respectively. SmBCO/IBAD-MgO coated conductors showed high critical current densities over 2.0 MA/cm2 with small amount of degradation by increasing the thickness of superconducting layer up to 3 ?m. The critical current of 637.5 A/cm-w (JC = 2.12 MA/cm2) at 77 K in self- field was obtained in 3 ?m-thick and 1 m long coated conductor. This is the highest critical current reported so far of the coated conductor with SmBCO superconducting layer deposited by co-evaporation.

Improving the numerical model for high temperature coated conductors using the Hall-probe measurement

Electric power applications of coated conductor tapes (e. g. power transmission cables, transformers, fault current limiters) are developed nowadays. Optimal design of these applications requires a realistic model of the electromagnetic behaviour of a single tape. We compare here four models that could represent the tape in electromagnetic calculations. The simplest model assumes a rectangular cross-section of superconducting layer and constant critical current density. Models that are more complex consider the critical current density depending on magnetic field and its orientation. Furthermore, one could introduce a non-uniformity of the superconducting layer across the tape width. We checked the predictive power of these models by comparing the agreement between the calculated values of magnetic field above the tape and the experimental data obtained by Hall-probe experiments. In the case of commercial coated conductor tape on non-magnetic substrate the most representative model incorporated the critical current density dependence on magnetic field as well as the assumption of worsening the layer properties towards the tape edges. The latter conclusion was confirmed by the experiment in which longitudinal strips cut from the tape were tested.

Spatially-resolved measurement on time-dependent electromagnetic behavior in alternating current carrying coated conductor

Establishment of processing technology for multifilamentary coated conductors (CCs) is a key issue for superconducting electric power applications from the viewpoint of AC loss reduction. On the other hand, CCs sometimes have local inhomogeneity in the superconducting layers, and that will cause a current blocking in a filament or inhomogeneity of critical current among filaments in a multifilamentary CC. Therefore, we need an assessment method for local electromagnetic behavior on AC loss properties of CCs. In this study, we developed a method for visualizing time-dependent AC loss distribution in CCs by using scanning Hall probe microscopy. We succeeded in visualizing local current density, electric field and loss density simultaneously with a spatial resolution of a few hundred micrometers. The measurement system has possible scanning area of 150×50mm2 and current capacity of 500A. This enables us to discuss the local electromagnetic behavior on a practical scale of CCs. We believe that this visualization method will be a very powerful tool to estimate the feasibility of processing technology for multifilamentary CCs.

R&D of coated conductors for applications in Japan

On the research and development of coated conductors in Japan, the Ic characteristics and the length have been remarkably improved in the national project. Five hundred meter-long tapes with higher Ic values than 300A/cm-width were realized by the pulsed laser deposition (PLD) and the metal organic deposition using trifluoroacetates (TFA-MOD) processings for the superconducting layer on the IBAD-GZO buffered substrates. In order to realize the low cost by the increasing the production rate of the ion beam assisted deposition (IBAD) layer, the process of IBAD-MgO was developed and a 1000m-long IBAD buffer tape was fabricated at an extremely high production rate of 1km/h. On the other hand, the artificial pinning center has been introduced in both PLD and MOD processing. The BaZrO3 nano-rods were aligned along the c-axis of GdBCO superconducting films by the PLD process. The Jc value in the magnetic field parallel to the c-axis was remarkably improved. Additionally, the BaZrO3 nano-particles were uniformly dispersed in YGdBCO films by the TFA-MOD process and the Jc–B–θ property was confirmed to be isotropic.Based on the above-mentioned achievements, the new national project, whose main objective is the development of some electric power applications using a coated conductor, started in 2008. In this project, the improvement of the coated conductor includes the five sub-themes: (1) degradation of tapes, (2) high Ic under magnetic field, (3) low AC loss, (4) high mechanical strength and high Je and (5) low cost and high yield.

AC losses in coated conductors

Future use of coated conductors in electric power applications like transmission cables,transformers or fault current limiters is sensitive to the amount of dissipation in the ACregime. This paper analyses factors controlling AC loss of coated conductors in typicalconfigurations: the self-field case when transport current generates the magnetic field, andthe case of AC applied field where the orientation of magnetic field with respect to thesuperconducting layer plays a significant role.We illustrate that a high-quality CC tape with non-magnetic substrate followsrather well the models developed for a thin strip. However, to meet an excellentagreement between experiment and theoretical prediction a detailed knowledgeof the superconductor properties is necessary and a numerical method must beinvolved.In the case of a superconducting layer deposited on a ferromagnetic substrate theoreticalpredictions give only basic directions and one must rely on numerical simulations entirely.We demonstrate that, with the help of a dedicated analysis of experimental data, very goodAC loss prediction is also possible for superconductor–ferromagnetic composites.Novel designs of coated conductor architectures can be developed in this way.

Thermal stability analysis of YBCO-coated conductors subject to over-currents

The thermal stability of superconducting YBCO-coated conductors subject to over-currentsare analysed. We have studied the effect of DC and AC over-current pulses inCu-stabilized and non-stabilized coated conductors by measuring the electric field andtemperature profiles of these conductors immersed in liquid nitrogen. Current pulses ofshort duration of about 90 ms and long duration of a few seconds were appliedto the samples. Three different cooling regimes of liquid nitrogen—convection,nucleate boiling and film boiling—were observed and their influence on the recoverytime of superconductivity in the coated conductors after the over-current pulseshas been analysed. We have studied the recovery behaviour under two differentconditions, in which the current was set to zero and to the operating currentafter the current pulses. These experiments simulated the conditions during anover-current situation in different electric power applications with special attention givento the behaviour of these coated conductors acting as in-fault current limiters.

Increase of the production rate and crystal growth mode ofGdBa2Cu3Oy-coated conductors using an in-plume growth technique for a reel-to-reel pulsed-laserdeposition system

We developed a new fabrication technique which we call the ‘in-plume growth (IPG)’ technique. AREBa2Cu3Oy layered film for a coated conductor (REBCO CC) is grown in the plume using a pulsed-laserdeposition (PLD) method with a short distance between the target and the substrate (dT−S) to increase the production rate. In general, the critical current density (Jc) of PLD-REBCO CCs using an RTR system decreases asdT−S decreases since the amount of the dead layer increases and the composition ofthe REBCO layer becomes off-stoichiometric. In this work, we fabricated high-Jc GdBa2Cu3Oy (GdBCO) CCs using the IPG technique by varying the target composition and the tapemoving speed to control the composition of the REBCO layer and to suppress the formation ofa-axis-oriented grains. As a result, the IPG-GdBCO CCs, which were fabricated at 2 m h−1 (depositionarea = 1-turn × 6.5 cm = 6.5 cm2, laserpower = 300 mJ,f = four-plumes × 30 Hz), showed the followingcharacteristics: Ic = 312 A cm−1 width (Jc = 2.6 MA cm−2)with 1.2 µm in thickness and 1 m length. The production speed and theJc value are 3.0 and 1.8 times higher, respectively, compared to those deposited understandard conditions without using the IPG technique. This result indicates that thePLD-REBCO CCs could be more competitive for production of CCs for practical electricpower applications in the near future.

A Silicon Micro Direct Methanol Fuel Cell Demonstrator Using Microfabrication Techniques

. This paper presents the design, microfabrication and characterizations of a silicon based, single-cell μDMFC demonstrator for micro/portable electrical power applications. The flow field plates of the fuel cell were made on 2“silicon wafers utilizing wet-etching and sputtering techniques. The fuel cell was assembled in an epoxy-based packaging process. Results show that a lower internal ohmic resistance of the fuel cell can be achieved with a thicker current collecting layer (CCL). Influence of the operating conditions on the μDMFC performance was also investigated. It was found that 2M methanol can yield a better fuel cell performance because it provided a better compromise between the methanol crossover and mass transportation during operation. On the other hand, a 4-time increase of the peak power density of the fuel cell was achieved by increasing the methanol temperature from 20°C to 80°C.

Power Hardware-in-the-Loop Testing of a YBCO Coated Conductor Fault Current Limiting Module

In recent years, good progress has been made in improving the quality and quantity afforded by the manufacturing process for YBCO coated conductors. As a result, several programs have started to develop electrical power applications like motors, transformers, and fault current limiters (SCFCL) with these conductors. High voltage resistive type SCFCLs may typically be assembled from modules connected in series and parallel to accommodate the required voltage and current levels. The limited length of such a SCFCL module simplifies the configuration, manufacturing, and maintenance. It also allows testing of these modules under laboratory conditions at reduced power levels. In order to test SCFCL modules under conditions they will experience in high voltage electrical networks, advanced test methods such as power hardware-in-the-loop (PHIL) can offer significant advantages. This method allows studying conditions such as voltage stability and severe system perturbations with the actual SCFCL module in the loop. Hence, the quench and recovery behavior of the SCFCL module can be investigated under conditions characteristic of real electrical power networks without elaborate experimental setups. This paper presents results from PHIL experiments with a SCFCL module consisting of an approx. 10 m coated conductor.

Second-Generation HTS Conductor Design and Engineering for Electrical Power Applications

Besides critical current and conductor length, thermal stability, mechanical properties and ac loss characteristics of second-generation (2G) HTS wire are very important performance parameters to electric power device applications. Each application sets specific technical requirements on conductors. The properties of the practical 2G HTS wire manufactured at SuperPower, Inc. have enabled satisfactory performance in a number of demonstration devices including cable, high-field magnetic coil and fault current limiter. Yet, effort is being made to develop new conductor structures and configurations toward further enhanced performance in order to extend the potential of 2G HTS wire over a wider application range. This paper describes a variety of newly developed configurations: striation, narrow width, low-resistance joints and high quality insulation. The performance of wire with new configurations will promote the wide use of 2G HTS wire.

Japanese efforts on coated conductor processing and its power applications: New 5 year project for materials and power applications of coated conductors (M-PACC)

Five years of Japanese national project (FY2003–FY2007) was ended last spring with remarkable success. The national project was originally aimed for development of coated conductors which have high superconductivity performance and long length enough to fabricate high temperature superconducting (HTS) electric power devices. Preliminary research and development of HTS electric power devices were carried out as well. A series of R&D results will be summarized and reviewed in this paper. The new 5 years Japanese national project has started last June (FY2008–FY2012) to develop HTS electric power applications including SMES, cables and transformers and to develop/produce coated conductors satisfying the requirements from the respective power devices. Collaborative R&D efforts by national laboratories, universities and private companies have been started with the supports of NEDO and METI. The accomplishment of the previous project will be summarized and the plans and goals of the new project will be presented in this paper.

Fuzzy logic control of stand-alone photovoltaic system with battery storage

Photovoltaic energy has nowadays an increased importance in electrical power applications, since it is considered as an essentially inexhaustible and broadly available energy resource. However, the output power provided via the photovoltaic conversion process depends on solar irradiation and temperature. Therefore, to maximize the efficiency of the photovoltaic energy system, it is necessary to track the maximum power point of the PV array. The present paper proposes a maximum power point tracker (MPPT) method, based on fuzzy logic controller (FLC), applied to a stand-alone photovoltaic system. It uses a sampling measure of the PV array power and voltage then determines an optimal increment required to have the optimal operating voltage which permits maximum power tracking. This method carries high accuracy around the optimum point when compared to the conventional one. The stand-alone photovoltaic system used in this paper includes two bi-directional DC/DC converters and a lead-acid battery bank to overcome the scare periods. One converter works as an MPP tracker, while the other regulates the batteries state of charge and compensates the power deficit to provide a continuous delivery of energy to the load. The Obtained simulation results show the effectiveness of the proposed fuzzy logic controller.

超伝導テープ線材の電磁応答―電流・磁場分布および交流損失の理論解析―

The electromagnetic response of superconducting tapes exposed to transport currents and/or applied magnetic fields is the key issue for electric power application of superconducting tapes. In this article, theoretical expressions on the current distributions, magnetic-field distributions, and ac losses of superconducting tapes are presented. Those expressions are derived on the basis of Bean's critical state model, and the thickness/width ratio of the superconducting layers is regarded as an infinitesimal. The analytical expressions for assembled conductors using superconducting tapes (i.e., stacks, coplanar arrays, and polygonally arranged tapes) are also presented.