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This paper proposes an application of superconducting flywheel energy storages (SFESs) to compensate the power fluctuation of the large scale wind farm. Based on the global interest against global warming, the power capacity of the renewable generation, especially wind generation, has been increased steeply. However, since wind generations depend on the natural wind speed completely, the power output cannot be controlled. The power fluctuation caused by the non-controllable output characteristic may create voltage problem for local system and frequency problem for whole power system. To solve those problems, the hybrid application of the large-capacity battery energy storage system (BESS) and the high-speed superconducting flywheel energy storage system (SFES) are considered in Heangwon wind farm in Cheju Island in Korea. Through the case studies based on the site-measured output data, the optimal power and energy capacity of the BESSs and SFES are figured out. [ABSTRACT FROM PUBLISHER]

This paper proposes a reliability model for a superconducting fault current limiter (SFCL), which is a new alternative in limiting the fault current recently increasing in a network. An evaluation technique for distribution reliability that uses the improved failure rate of all protective devices in a network, depending on the location of the SFCL, is also proposed. As a result, it is expected that the SFCL makes the reliability of adjacent equipment on an existing network improve, and these changes are analyzed. In addition, in order to apply the effect of the intermittent output of renewable-energy sources, distribution reliability indices were redefined in this paper. Case studies verify that the SFCL is effective in reducing fault currents and improving distribution reliability. These effects are analyzed with respect to the location of the SFCL in a case study system. [ABSTRACT FROM AUTHOR]

With the continuing improvements in HTS conductors, the application to power distribution transformers becomes possible as well as economical. To realize a viable design, many system aspects must be addressed including the thermal and dielectric characteristics of the winding insulation. This work reports on the study of cellulose-based dielectric insulation and transformer-board for dry-type (conduction cooled), 50 kVA to 5000 kVA, medium-voltage, high-temperature superconductor transformers. Results of electric-field strength studies and tests are presented. [ABSTRACT FROM AUTHOR]

Superconducting fault current limiters (SFCL) have already demonstrated their viability in electric power grids. The growth in distributed generation sources and an increased interconnection of networks tend to increase the complexity of electric power grids, rising the number of failures, especially short circuits. To disseminate these technologies, the development of straightforward design tools is required. These tools must consider the properties of the available constitutive elements of the devices. A design methodology that allows modeling and optimizing saturated cores SFCL is presented in this paper. This methodology considers the characteristics of each constitutive element of the limiter while addressing utility requirements and power grid characteristics. Genetic algorithms are used both to optimize the constitutive elements of the limiter and its performance in the power grid. In order to validate this methodology, a three-phase SFCL is designed, optimized, and simulated. [ABSTRACT FROM AUTHOR]

As superconducting magnetic energy storage (SMES) and battery are complementary in their technical properties of power capacity, energy density, response speed, etc., this paper proposes an SMES-battery energy storage system to stabilize a photovoltaic-based microgrid under different faults. The related theoretical modeling is stated, and the control and coordination methods of the SMES-battery are put forward. Using MATLAB, a comparison of with the SMES-battery and only with the battery is carried out. From the main specifications of the SMES magnet, the ac-loss calculation is also performed. The results show that i) the SMES-battery is better than the battery to timely deal with the transient faults of the microgrid; ii) the SMES-battery enables to ensure a seamless mode-transition for the microgrid under the external fault, and reduce the fault current in the point of common coupling to avoid an unnecessary off-grid under the internal fault; and iii) the SMES magnet's ac-loss power has a maximum value of 380 W, and it is acceptable for the future design of conductioncooled structure and cryogenic system. [ABSTRACT FROM AUTHOR]

This paper presents a study on design technique of superconducting fault current limiters (SFCLs) with a bypass reactor. The SFCL system consists of a non-inductive superconducting coil and a copper coil as a bypass reactor. Since typical resistive SFCL impedance is too high to adopt the existing grid protection scheme, a bypass reactor is required to adjust the impedance. The superconducting coil is a current-driven passive element; hence, connecting a bypass reactor in parallel affects the current sharing between the superconducting coil and the copper reactor. We proposed a design technique to estimate the generated impedance considering the current sharing. The technique is based on a SPICE simulation and thermal finite element analysis (FEA). By comparing to the test result with two kinds of bypass reactors, it is confirmed that the proposed method can simulate all currents and voltages properly. As a result, a case study was conducted on the design of the SFCL system, rated on 13.2 kV/2.5 kA was being considered as a new distribution grid in Korean metropolitan areas. [ABSTRACT FROM PUBLISHER]

The superconducting motor generally adopts superconducting magnets to supply high flux density in the air-gap around the rotor. This structure can decrease the volume as a result of the high magnetic load, but it also creates cooling difficulty problems due to the cooling medium's spin sealing. Therefore, the superconducting magnets need frequent maintenance, and this structure cannot be applied in the industry field. So a novel high temperature superconducting motor with a superconducting armature coils is researched. This motor's stator uses ferromagnetic material and the superconducting windings are located in the slots. The ferromagnetic material can decrease the magnetic field in the superconducting coils, so the current carrying ability of the superconducting coils can be increased. The rotor adopts the permanent magnets as the excitation. Such design details of the motor can ensure the superconducting coils can undertake larger current and reduce AC loss. In this paper the electromagnetic field distribution of the HTS motor stator coils is analysed. Finally, the detailed HTS motor parameters are presented to analyse the output torque characteristic. From the characteristics, it can be seen that the novel HTS motor has the same power density as the traditional HTS motor. [ABSTRACT FROM PUBLISHER]

The GENI project for applying the 22.9 kV HTS cable and the SFCL to real power system has been progressed in South Korea since 2008. The HTS power devices were applied to the Icheon substation in the real Korean power grid in August 2011. This is the first demonstration of HTS power devices in South Korea. For a successful application, this paper proposes proper specifications of a current limiting resistor/reactor and an activating current for the 22.9 kV SFCL in the Korean power distribution system. These specifications are determined, considering the protection system of real Korean power system. [ABSTRACT FROM PUBLISHER]

In this paper, the application method of superconducting fault current limiter (SFCL) for the protection coordination of the protective devices in a power distribution system was analyzed. The SFCL has been announced as better solution among many methods to limit a fault current effectively, which has continuously increased due to more complex network of a power system. However, the application of the SFCL in a power system affects the operation of the protection devices and the protection coordination, which requires the study on the protection coordination of the protective devices considering the application of the SFCL in a power distribution system. [ABSTRACT FROM PUBLISHER]

Superconducting fault current limiters (SFCLs) may play an important role in power-dense electrical systems. Therefore, it is important to understand the dynamic characteristics of SFCLs. This will allow the behavior of multiple SFCLs in a system to be fully understood during faults and other transient conditions, which will consequently permit the coordination of the SFCL devices to ensure that only the device(s) closest to the fault location will operate. It will also allow SFCL behavior and impact to be taken into account when coordinating network protection systems. This paper demonstrates that resistive SFCLs have an inverse current–time characteristic: They will quench (become resistive) in a time that inversely depends upon the initial fault current magnitude. The timescales are shown to be much shorter than those typical of inverse overcurrent protection. A generic equation has been derived, which allows the quench time to be estimated for a given prospective fault current magnitude and initial superconductor temperature and for various superconducting device and material properties. This information will be of value to system designers in understanding the impact of SFCLs on network protection systems during faults and in planning the relative positions of multiple SFCLs. [ABSTRACT FROM AUTHOR]

In this paper, we describes how to coordinate between recloser and fuse in power distribution system with superconducting fault current limiters (SFCL). The recloser and fuses are the main overcurrent protective devices in power distribution system. Universally, to protect against permanent faults, fuses are installed on overhead feeder laterals and the reclosers as a backup protection against temporary faults remove many unnecessary outages. Here, the recloser is set to trip using TCC curve for a temporary fault before any of the fuses can melt. If the fault is a permanent fault, the fuse has to melt just before the last delay trip of the recloser. However, the application of a resistive SFCL in power distribution system affects the recloser- fuse operation and coordination as decreased fault currents. In case that when a permanent fault occurs, the recloser could be locked-out after the last delay trip before the fuses operate. [ABSTRACT FROM AUTHOR]

Since the hybrid superconducting fault current limiter (SFCL) to solve the problems such as the larger volume of the superconducting components and the slow recovery time after the fault is removed has been developed, the plans to apply the hybrid SFCL into the real electrical power grid have been reported. Especially, the discussion for the protection coordination between the existing protective devices due to the introduction of the hybrid SFCL is more required together with the review from the whole viewpoint of the power system. In this paper, the experimental devices to simulate the operation of the hybrid SFCL as well as the protection coordination between the protective devices such as the over-current relay (OCR) were constructed and the protection coordination of the hybrid SFCL with the protective devices was analysed through the experiments. Through the analysis on the experimental results, among the various components comprising the hybrid SFCL, the current limiting resistor (CLR) was confirmed to affect the protection coordination between the OCR and the hybrid SFCL and the method to keep the protection coordination between the hybrid SFCL and the protective devices was discussed. [ABSTRACT FROM AUTHOR]

This paper assesses and analyses the effects of superconducting fault current limiter (SFCL) installed in power distribution system on voltage sags. First of all, resistor-type SFCL is modeled using PSCAD/EMTDC to represent the quench and recovery characteristics based on the experimental results. Next, typical power distribution system of Korea is modeled. When the SFCL is installed in various locations from the starting point to end point of feeders, improvement of voltage sag is evaluated using the Information of Technology Industry Council (ITIC) curve of customer's loads when a fault occur. Finally, future studies needing to apply SFCL to power distribution system are presented [ABSTRACT FROM AUTHOR]

The power grid, especially distribution grid, has been more complicated due to distributed generations (DGs) with renewable energy sources and the smart grid. The complexity changes two things in terms of a fault; higher prospective fault current and the temporal variation of sources and loads. To correspond to those remarkable changes, we propose a fault current controller (FCC) named “smart FCC.” The smart FCC consists of a superconducting coil with a freewheeling diode if necessary, four thyristors, and a control unit. Smart FCC can not only limit but also control the current when a fault occurs. The smart grid technology can provide so enough information that it is possible to estimate which level of limited current should be the best in the real-time situation of the grid. Based on a real-time calculation of optimal fault current using the smart grid monitoring technologies, this new device is always ready to adjust the fault current. In this paper, we introduce a concept of the smart FCC and prove the concept. Various topologies have been proposed and simulated. Finally, a case study on a distribution class of 22.9 kV smart FCC has been conducted based on a conceptional system design. [ABSTRACT FROM AUTHOR]

A multi-laminated HTS tape conductor has been recently developed to fabricate large double pancake coils. If the HTS tapes are simply laminated to form the conductor, the current distribution in the laminated tape conductor of the coil is unbalanced because of different inductances of all tapes. It is very important to analyze current distributions in the multi-laminated tape conductor used for the double pancake coil for SMES. In this paper, we analyze the current distribution in the tape conductor by using electrical circuit model, and then discuss how to obtain the homogeneous current distribution. One way is to transpose the tape position at both ends of pancake coil so as to arrange the tapes symmetrically. However, this method is not perfectly geometrical symmetry for more than 3 laminated tapes in the conductor. We propose new method to obtain homogeneous current distribution by adjusting gaps between HTS tapes in the conductor. Finally we numerically demonstrate the homogeneous current distribution in the 4-laminated tapes with inserting additional thickness among tapes. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new method for imaging the distribution of electric currents; this method involves a combination of ultrasonography and SQUID magnetometry. To evaluate this new method, we used a block of gelatin pierced through by a lead wire as a model of a biological object. An electric current was applied to the wire and the magnetic signal generated around the wire was measured by a superconducting quantum interference device (SQUID). At the same time, an ultrasound image of the wire was taken by means of an ultrasound imaging machine. Subsequently, the magnetic field image was aligned with the ultrasound image with respect to the position of marker coils relative to the ultrasound probe. The source of the magnetic signal was localized by solving the inverse problem and visualized on the ultrasound image of the wire. The position error was 2.9 mm. The results demonstrated the applicability of the new technique combining SQUID magnetometry with ultrasound imaging. [ABSTRACT FROM AUTHOR]

As one of the countermeasures to solve the increase problem of the fault current in a power system, the superconducting fault current limiter (SFCL) has been noticed as the attractive device because it has no power loss in a normal time and can limit the fault current rapidly without additional device to detect the fault current. However, the introduction of the SFCL in a power distribution system affects the protection coordination between the existing protective devices such as the over-current relay (OCR) and the recloser, which causes the operation of the protective devices to get out of their original setting values. Therefore, the analysis on the effect of the SFCL introduction on the existing protective devices is required and the method to keep the protection coordination between the protective devices in a power system with the SFCL should be first considered. In this paper, the protection coordination experiments between the OCR and the recloser in the simulated power distribution system with the SFCL were performed. Based on the experimental results, the influence of the SFCL on the operation of these protective devices was analysed and the methods to keep the protection coordination between the OCR and the recloser in a power distribution system with the SFCL were discussed. [ABSTRACT FROM AUTHOR]

Superconducting Fault Current Limiters (SFCLs) are able to reduce fault currents to an acceptable value, reducing potential mechanical and thermal damage to power system apparatus and allowing more flexibility in power system design and operation. The device can also help avoid replacing circuit breakers whose capacity has been exceeded. Due to limitations in current YBCO thin film manufacturing processes, it is not easy to obtain one large thin film that satisfies the specifications for high voltage and large current applications. The combination of standardized thin films has merit to reduce costs and maintain device quality, and it is necessary to connect these thin films in different series and parallel configurations in order to meet these specifications. In this paper, the design of a resistive type SFCL using parallel-connected YBCO thin films is discussed, including the role of a parallel resistor and the influence of individual thin film characteristics, based on both theory and experimental results. [ABSTRACT FROM AUTHOR]

According to the recent design of an HTS (High Temperature superconducting) power application whose capacity is hundreds MVA, the rated current is over thousand amps. Considering the performance of the recent HTS tapes, it is inevitable to use several HTS tapes in parallel for high capacity current. In this paper, we have investigated the influence of current distribution on the AC loss in the multi-stacked superconducting wire. The dependence of AC loss and critical current on the current distribution in multi-stacked wires was discussed. We fabricated multi-stacked wires and measured the current distribution at 77 K. The current distribution was indirectly found from the self-field distribution. The magnetic field was measured by an array of hall sensors located around the HTS superconducting wires. In the case of non-uniform distribution of current, the performance of multi-stacked HTS wires is worse than that of uniform current distribution. [ABSTRACT FROM AUTHOR]

The transverse resistivity among filaments is a crucial parameter of composite superconducting wires, since it affects the coupling losses in ac regime, the current transfer length of the wire subjected to bending strain, and the current redistribution among filaments in the case of a quench. A direct measurement of the transverse interfilament resistance as a function of temperature in several \Nb3 \Sn multifilamentary wires was performed by means of a 4-probe method. This paper deals with the numerical analysis of the measurements performed on a OCSI wire manufactured by Luvata, containing 82 superconducting subelements each made of 150 filaments. The measurements are analyzed by applying a 2-D FEM of the wire cross-section and a 3-D electrical circuit model of the wire sample. The results obtained have been compared with those found on two other \Nb3\Sn wires with different architecture and a NbTi wire taken as a reference. [ABSTRACT FROM PUBLISHER]

For a power distribution system with distributed generation (DG) units, its fault current and induced overvoltage under abnormal conditions should be taken into account seriously. In consideration that applying superconducting fault current limiter (SFCL) may be a feasible solution, in this paper, the effects of a voltage compensation type active SFCL on them are studied through theoretical derivation and simulation. The active SFCL is composed of an air-core superconducting transformer and a PWM converter. The magnetic field in the air-core can be controlled by adjusting the converters output current, and then the active SFCLs equivalent impedance can be regulated for current-limitation and possible overvoltage suppression. During the study process, in view of the changes in the locations of the DG units connected to the system, the DG units injection capacities and the fault positions, the active SFCLs current-limiting and overvoltage-suppressing characteristics are both simulated in MATLAB. The simulation results show that the active SFCL can play an obvious role in restraining the fault current and overvoltage, and it can contribute to avoiding damage on the relevant distribution equipment and improve the systems safety and reliability. [ABSTRACT FROM PUBLISHER]

The high temperature superconducting (HTS) power cable has been successfully installed and operated for feasibility confirmation since 2006 at the power testing center of Korea Electric Power Corporation (KEPCO). The three phase 100 m long HTS cable with 22.9 kV/1.25 kA was manufactured and cooled by the open-loop of sub-cooled liquid nitrogen generated by a decompression cooling unit. No major fault has been observed during long-term operating test. As a next step, the design study of a 500 m long HTS cable system has initiated in 2008. Now, the HTS power cable was manufactured and installed at Icheon substation located near Seoul. In this paper, the cooling performance test of the 500 m long HTS cable in the real power grid is reported. Pre-cooling process using nitrogen gas is presented and the result of initial cool-down of the HTS cable is reported. Also, temperature as well as pressure drop in the system is discussed with respect to the loading current level. [ABSTRACT FROM PUBLISHER]

A method for estimating the current distribution on the HTS strands which is composed of the HTS power cable was developed. A group of hall sensors which are well-arranged around the HTS cable were used in measuring the circumferential magnetic field. The current distribution can be calculated by solving a matrix equation which contains the measured magnetic field values as its elements. The contribution of the magnetic field generated by each strand in each hall sensor should be known to solve the matrix equation. The contribution can be calculated by FEM analysis simulating the HTS cable or can be measured using a duplicated short HTS cable of which current terminals are modified to apply the current to each strand independently. A simple computer simulation was performed to investigate the feasibility of the method and the performance characteristics of the method was examined for the HTS cable which is composed of several HTS strands. In this paper, a simple mathematics for estimating the current distribution and the results of experiment using the designed and manufactured measuring apparatus will be introduced. [ABSTRACT FROM AUTHOR]

In this paper, we analyzed recloser to fuse protective coordination when superconducting fault current limiters (SFCL) are applied into power distribution system. Generally, fuses are installed at more remote position from substation than reclosers. Thus, when instantaneous faults occur at the point behind the fuse, the fuse doesn't melt because the recloser removes the fault by reclosing operation. When permanent faults occur, the fuse has to melt just before the last delay trip of the recloser in order to prevent the loads between the recloser and the fuse to be interrupted. However, in power distribution system with SFCL, the fault current is decreased by the effect of the impedance of the SFCL. In this case, when a permanent fault occurs, the fuse may not melt during the delay operation of the recloser because of the insufficient heat from the decreased current. As a result, the recloser is locked-out and the loads between the recloser and the fuse are interrupted unnecessarily. Therefore, when SFCLs are applied into power distribution system, the rating of fuse has to be reselected to coordinate recloser-fuse effectively. However, this reselection for the protective coordination becomes very complicated problem considering the impedances of generator, transformer, distribution line, fault and so on. To solve these problems, we proposed the method to calculate and select the ratings of fuse using the above-mentioned impedances. The proposed method will be proved through the case studies. [ABSTRACT FROM AUTHOR]

Enlarging the electric power supply capacity of 22.9 kV distribution line by upgrading the main transformer from 60 MVA to 100 MVA has been under consideration in order to cope with increasing electric power demands of distribution line in Korea which aims to replace some 154 kV supply demands by 22.9 kV large-capacity distribution systems. In this case, the prospective fault current of 22.9 kV distribution line is much bigger than the rated withstand fault current level of conventional electric equipments. As a major feasible solution to reduce excessive fault current, superconducting fault current limiters (SFCLs) are considered to be installed at 154 kV/22.9 kV substation. But until now, certified specifications or test procedures were not available considering utilities' requirements. And the performances of various types of SFCLs were not deeply investigated regarding the reclosing scheme of conventional networks. In this paper, in order to determine the suitable type of SFCL for newly installed 22.9 kV large distribution line in Korea, requirements and specifications of SFCLs were proposed considering the installation spots of large-capacity distribution line. Four types of SFCLs were modeled and analyzed using EMTP and their performances focusing on the coordination with reclosers were investigated to verify the suitability into the large-capacity distribution line. Consequently, detailed specifications and expected installation sites were proposed and suitable types of SFCLs for 22.9 kV large-capacity distribution line were suggested. [ABSTRACT FROM AUTHOR]

YBCO superconducting wire has a relatively low decrease in power distribution at high temperatures and under a high magnetic field. A high-intensity substrate is used for the wire, so the wire has high machine characteristics. Therefore, it is expected that this wire can be used for large-scale high magnetic field coils. Here, coordination between the SMES system for 100 MVA/2 GJ class load fluctuation compensating was conducted using IBAD/CVDYBCO wire. The SMES system includes a toroidal type YBCO coil consisting of 180 compact, high magnetic field multi-unit coils, a large coil cooling system that uses the conduction cooling method, which does not use a refrigerant medium, and a multi-cell power converter that achieves multi-unit coil connection with relatively low current and low voltage. Studies were conducted for each individual device and for the whole system. Based on the study plan in this paper, it has become possible to develop and coordinate each device of the 100 MVA/2 GJ class power system load fluctuation compensation SMES system using YBCO wire, which up until now had seem impossible as an actual system. [ABSTRACT FROM AUTHOR]

In order to meet the needs of economical and stable power supply and high current density cable with compact size, several countries carry out researches on High Temperature Superconducting (HTS) cables. Korea Electric Power Corporation (KEPCO) established the HTS cable test center and installed 22.9 kV, 1250 A, 50 MVA, 100 m class HTS cable system to investigate the performances and application possibility in real power grids. The HTS cable system went through seven cool down and warm-up cycles and also many kinds of performance tests. for 3 years. Rated voltage-current tests, over voltage tests, and measurements of heat loss and AC loss with various currents have been examined. Moreover, DC critical current tests were performed for checking conductor degradation before warming up or after cooling down. Through the performance tests of the HTS cable system, the overall efficiency and loss factors are estimated and compared with conventional power cables in this paper. We conclude the present status of HTS cable system and application possibility in the real power grid. [ABSTRACT FROM AUTHOR]

One of the most important issues in the design of a HTS power cable is the induced current between conducting and shield layers under fault condition. The current distribution of conducting and shield layers is changed due to the fault current. Conducting and shield layers are coupled magnetically. The analysis of current distribution in HTS power cable requires understanding of the magnetic coupling between the conducting and shield layers. In order to study the phenomenon mentioned above, a solenoid type of HTS power cable model which includes both conducting and shield layer is actually manufactured in this paper. The current distribution of conducting and shield layers is evaluated by real manufactured solenoid type of HTS power cable model. The results obtained through the experiment and analysis would provide important data for the design of HTS power cables and valid information for their installation in power system. [ABSTRACT FROM AUTHOR]

This paper presents a study of the effects of opening up the midplane in conventional sector coil dipoles, also known as cos ϴ-designs. The open midplane design is a candidate for the higher luminosity upgrade for the LHC, and also for the future beta beam project at CERN, which has the heat deposition mainly concentrated in the midplane of the dipoles. By opening up the midplane, the major part of the spray particles can be avoided, allowing the use of strong superconductive magnets. The aim of this study is to maintain good field quality after a gap in the midplane has been inserted. Short sample field and the electromagnetic force distribution will also be presented for some solutions. [ABSTRACT FROM AUTHOR]

The discovery of high-temperature superconductors were the great opportunity for developing fault current limiters using quenching phenomena. Superconducting fault current limiters is highly effective solutions to reduce and control excessive fault current which is inevitable to electric power systems. So, many companies and national research institutes were trying to develop this novel electric equipment under the assistance of national government. Due to their efforts, various types of superconducting fault current limiters were designed and tested. But, unfortunately, the practical applications and commercialization of superconducting fault current limiters are pending due to many unsolved problems. This paper discusses the current issues and commercialization problems of superconducting fault current limiters considering various aspects such as coordination with conventional relay, high voltage and high current issues, performance, cost, size, and life and maintenance issues. Then, emerging solutions for fault current limiters using hybrid method were introduced and analyzed. Finally, the viable method and our newly developed hybrid superconducting fault current limiters in order to solve the practical problems of conventional superconducting fault current limiters was briefly introduced. [ABSTRACT FROM AUTHOR]

This paper describes the numerical results of AC losses in various types of non-twisted multifilamentary tapes that actual Bi-2223 Ag-sheathed wires are idealized. The penetration process of magnetic flux into the superconductor filaments subject to Bean's critical state model is simulated for the application of an external transverse magnetic field perpendicular to the broadest face of tape wire by means of energy minimization. The AC losses under cyclic fields are calculated from the distribution of a vector potential in an initial state. The influences of arrangements and shapes of the filaments on the losses are investigated as compared with those for a wire that the entire filamentary region is regarded as a homogeneous superconductor. [ABSTRACT FROM AUTHOR]

A superconducting fault current limiter (SFCL) in series with a downstream circuit breaker could provide a viable solution to controlling fault current levels in electrical distribution networks. In order to integrate the SFCL into power grids, we need a way to conveniently predict the performance of the SFCL in a given scenario. In this paper, short circuit analysis based on the electromagnetic transient program was used to investigate the operational behavior of the SFCL installed in an electrical distribution grid. System studies show that the SFCL can not only limit the fault current to an acceptable value, but also mitigate the voltage sag. The transient recovery voltage (TRV) could be remarkably damped and improved by the presence of the SFCL after the circuit breaker is opened to clear the fault. [ABSTRACT FROM AUTHOR]

The increasing electricity demand and deregulation of the power industry continues to produce problems for transmission and distribution system operators who are faced with curtailing investment and the NIMBY (Not In My Back Yard) phenomena [1], [2]. It is expected that the route length per MW demand of South Korea will decrease gradually from 0.57[C-km/MW] to 0.53[C-km/MW] in 2017 [3]. This comes up to a real serious problem from system planning and operation viewpoints. HTS technologies related to power system have properties to solve these complex transmission and distribution constraints, especially for metropolitan area, in the future. As the HTS technology has developed, the HTS cable technology can be the most effective alternative to solve the future expected power network constraints. This paper describes the application methodology of developing 22.9 kV HTS cable by CAST (the Center for Applied Superconductivity Technology) for practical distribution system. 22.9 kV HTS cable under development with step-by-step application methodology can substitute the existing and planning conventional 154 kV cable [4], [5]. If this scheme is applied, part of downtown 154 kV substation of metropolitan city such as Seoul can be changed into 22.9 kV switching station. Additionally, it can give huge economic, environmental benefits to all of the concerned authorities. [ABSTRACT FROM AUTHOR]

This paper presented numerical studies on layer-to-layer current distributions and AC losses in triaxial multi-layer three-phase cable conductors. The simulations were performed for triaxial cables of 2-layer/phase configurations with several combinations of twist pitch to investigate the influence of the cable twist configuration on the layer-to-layer current distribution and the AC loss under 3-phase AC operation. From the numerical results, it was shown that the twist pitch combinations for uniform layer-to-layer current distributions could be found. The numerical results also showed, however, that the AC loss can not be reduced by equalizing the layer-to-layer current distribution. The reason is clarified from the numerical data of the current density profiles across the superconducting layers. For the cable design, it is necessary to select proper twist configuration considering not only the equalization of current distribution but also the minimization of AC loss. [ABSTRACT FROM AUTHOR]

A team consisting of SuperPower, Inc. (HTS systems manufacturer), The BOC Group (global industrial gases company), Sumitomo Electric Industries (cable manufacturer), and Niagara Mohawk (electric utility) is developing a 34.5 kV HTS cable for installation in the distribution network in downtown Albany, NY. Energization is projected for the winter of 2005. The cable will be rated for 800 Arms, with all three electrical phases in one cryostat. The 350 m long cable will be pulled through a duct that includes a 90° bend. A field installed underground cable joint will allow for the replacement of a 30 m section of the original first generation HIS cable with a section manufactured utilizing second generation superconductor, in 2006. This paper will summarize the progress made to date and outline future development work. [ABSTRACT FROM AUTHOR]

Currently, when a new fabrication process becomes available, all logic cells have to be re-designed, re-optimized and laid out from scratch. This is a manual and lime intensive process, which hampers the migration of RSFQ circuits to better fabrication processes. The paper investigates the parameters that are required to specify logic gates that are technology and fabrication process independent Ways of automating the optimization of the logic gates for implementation in new technologies, and automating the layout of logic cells for new design rules or new fabrication processes, are described. Cells can then be characterized for implementation in both LTS and HTS processes. Steps in the development of new logic gates and automation processes are shown. [ABSTRACT FROM AUTHOR]

In this paper we investigate AC-transport current loss and current distribution of Bi-2223/Ag tapes which are arranged in edge-to-edge configuration. A numerical code was developed to estimate the transport current loss and the current distribution across the tapes. AC-loss measurements were also performed and the coincidence between the calculated and measured values is excellent. AC losses of the horizontally-attached tapes were larger than just a simple summation of each tape's loss but not as large as the loss from Norris equation. Discussions on these results are addressed using the current distribution obtained from numerical analysis. [ABSTRACT FROM AUTHOR]

Since 1999, a Japanese national project to realize commercially feasible SMES for designated applications has been promoted. Model coils for power system stabilization, load fluctuation compensation and frequency control have been fabricated and tested. In this paper, we introduce the present status of the project, including feasibility studies of an HTS SMES. [ABSTRACT FROM AUTHOR]

It is highly beneficial to reduce AC losses in multi-layer superconducting power cables. For this purpose, each superconducting layer is wound with a different twist pitch on a former so as to balance current distribution among layers. Finite element analysis makes it possible to show electromagnetic properties in superconducting layers visually, which is useful for discussing methods to enable further loss reduction. However, making a numerical analysis model of a multi-layer cable which is faithful to its geometry is highly complicated and troublesome as the model requires a correction each time the set of twist pitches needs to be changed. The authors have developed a new method to analyze such a cable by introducing anisotropy on the conductivity. In this paper, the method and the effects are discussed and compared with experimental results. [ABSTRACT FROM AUTHOR]

In recent years the problem of current distribution in multistrand superconducting cables has received increasing attention for large scale superconductivity applications due to its effect on the stability of fusion magnets and the field quality of accelerator magnets. A modeling approach based on distributed parameters has revealed to be very effective in dealing with long cables made of some tens or hundreds of strands. In this paper we present a fully analytical solution equation for a distributed parameters model in cables made of an arbitrary number of strands, whose validity is subjected to symmetry conditions generally satisfied in practical cables. We give in particular analytical formulae of practical use for the estimation of the maximum strand currents, time constants and redistribution lengths as a function of the cable properties and the external voltage source. [ABSTRACT FROM AUTHOR]

In Japan, superconducting cables for the direct current railway electrification systems have been progressively developed. When superconducting cables are used as a feeder of the railway electrification system, the voltage drop could be significantly reduced. However, fault current due to short-circuit and the like should be enhanced since superconducting cables have no resistance. In this study, it is proposed that superconducting transformers with current limiting function are applied as rectifier transformers so that the fault current can be suppressed. Although superconducting feeding system has many effects, the rated secondary current of the rectifier transformers is very large. So the current capacity of the secondary windings of the rectifier transformers should also be enhanced up to several kA. To realize that, transposed parallel conductors composed of HTS tapes are expected to be adopted. For low ac loss and uniform current sharing among the tapes, the constituent tapes of parallel conductors need to be transposed so that their inductances balance each other. In this paper, the optimum transposition method in the case where a 32-tape parallel conductor is wound into a single-layer solenoid is investigated by the numerical simulation of the current sharing among the constituent tapes and the validity is verified experimentally. [ABSTRACT FROM PUBLISHER]

The introduction of various dispersed generation (DG) in a power distribution system has caused the short-circuit current to increase, which can make the operation of the protective device deviate from its original set value. Especially, the increase of a short-circuit current in a power distribution system due to the increase of the DG is expected to be required for the related power utilities such as the circuit breaker to be replaced with a larger one. Among the countermeasures to solve the short-circuit problem in a power distribution system considering the increase of the DG, the superconducting fault current limiter (SFCL) has been noticed as one of the promising devices. [ABSTRACT FROM PUBLISHER]

The current distribution and stability of low temperature superconductor (LTS) and high temperature superconductor (HTS) hybrid superconductor, made of NbTi wire and YBCO coated-conductor, are described. The current distribution, quench propagation velocity (QPV) and the minimum quench energy (MQE) are numerically analysed by finite element method (FEM) based on the different power-law models since the n value in LTS is much larger than that in HTS. It is shown that the transport current in LTS is larger than in HTS if both of them have the same critical currents, and the ratio of transport current in LTS to that in HTS decreases with increase of the total transport current near their critical currents. The stability of the hybrid NbTi/YBCO composite conductor is also simulated, which indicates that MQE in the hybrid conductor is much higher than in NbTi wire but smaller than in YBCO conductor. However, the quench propagation velocity is in the range of low-temperature superconductor through the high-temperature superconductor. With advantages of high engineering current density and improvement of stability, the hybrid superconductor is expected to have potential application in large scale magnet and conducting-cooled magnet particularly. [ABSTRACT FROM AUTHOR]

We have proposed continuously transposed coated conductor (CTCC) in striation for power devices reducing AC loss. It consists of a number of coated conductors with filaments made by striation. The transport of current may distribute non-uniformity in the filament particularly while CTCC conducts AC current. The array of Hall sensors is capable of measuring the current distribution in the filaments and in conductors. However, the search coil array may be applied as ersatz for Hall array in case of existing AC current. The filamentary CTCCs are prepared and the current distribution is then measured by the array of search coils. [ABSTRACT FROM AUTHOR]

DFBX distribution boxes provide cryogenic and electrical services to superconducting quadrupoles and to a superconducting dipole at either end of four of the long straight sections in the LHC. The DFBX boxes also provide instrumentation and quench protection to the magnets. Current for the quadrupole and the dipole magnet is delivered through leads that combine HTS and gas cooled leads. Current for the 600 A and 120 A correction magnets is provided by pure gas-cooled leads. The bus bars from the leads to the magnets pass through low leak-rate lambda plugs between 1.8 K and 4.4 K. The heat leak into the 1.9 K region from the liquid helium tank is determined by the design of the lambda plugs. This paper describes the DFBX boxes and their function of delivering current and instrumentation signals to the magnets. [ABSTRACT FROM AUTHOR]

In order to quantitatively elucidate the transport characteristics of HTS conductors with large current capacities, we minutely investigated the relation between the current distributions in the sample conductor and the circuit parameters such as joint resistance and sample inductance. A high temperature superconducting current transformer (HTS-CT) was used to energize a large current in the sample conductor. No change in the joint resistance was observed with an increase of the sample current. On the other hand, the current ratio of the HTS-CT decreased with an increase in the sample current. This is considered to be equivalent to the inductance becoming large with an increase in the sample current. From the measured current distributions, we see that the current in the central area of the conductor is increased with increasing sample current. Based on these experimental results, the relation between the change of the current distributions and the increase of the sample inductance is discussed. [ABSTRACT FROM PUBLISHER]

Key components for the power transmission and distribution for the future grids are superconducting cables. The energy network in highly populated areas will soon fully benefit from this technology, in particular for the retrofitting of the existing cables. However retrofitting the existing grid in underground structures (pipes, pits, turn), requires cables as small a diameter as possible. The HTS cable core is generally manufactured by laying tapes around a former with a diameter of about 25 mm to prevent any damage to the tape during the cabling and the handling operations. However in this configuration, the former cannot be used to transport the current. This triggered a new approach in cable design involving round 2G HTS wires with a diameter from 1 to 2 mm. They can be assembled to build a small cable core with a high ampacity. The benefits of this new wire design on power cables are discussed. The first results on different manufacturing processes and the characterizations of the 2G HTS wires are presented. [ABSTRACT FROM PUBLISHER]

The increase of various dispersed generations (DGs) such as wind power and solar cell in a power distribution system has been reported to increase the short-circuit current. In addition, the introduction of the DG in a power distribution system is expected to affect the operation of the protective device as well. The superconducting fault current limiter (SFCL), which has been continuously studied for the reduction of the circuit breaker's power burden, recently starts to be noticed as effective method to solve the fault current problem due to the introduction of the DG. Since the fault current limiting operation of the SFCL and the operations of the protective devices such as the over-current relay or the recloser are affected by the application location of the DG, the study on the protection cooperation of the protective devices with the SFCL considering the application location of the DG in a power distribution system is firstly required. [ABSTRACT FROM PUBLISHER]

In this study, we analyse the coordination of protective relays between a primary feeder and an interconnecting transformer grounded by using a superconducting fault current limiter (SFCL) of a wind farm. Most wind farms and utility systems are interconnected by a transformer. The winding configuration of most interconnecting transformers is wye grounded-delta. Therefore, the utility-side grounding of the interconnecting transformer can support a new single line-to-ground fault current path. Because the coordination plan of a protective relay in a power distribution system does not consider the new fault path, an unintended relay operation can occur. To overcome this problem, an SFCL is applied to the ground connection of the interconnecting transformer. We analyse the effect of the resistive SFCLs on the coordination of the ground faults using time-domain transient simulation software (PSCAD/EMTDC). [ABSTRACT FROM PUBLISHER]

Two groups of superconducting power transmission cables composed of two layers of coated conductors with 4 mm width and 2 \mum superconductor-thickness have been designed. In one group, four styles of unevenly distributed critical currents (Ic) are applied, while in the other group there is one damaged coated conductor in each cable. Trapezoidal critical current density (Jc) distribution with a sloping shoulder of 0.3 mm is assumed while calculating the AC losses of these cables numerically by using a one dimensional FEM model. Numerical results show that unevenly distributed Ic increase AC losses along with the increasing variance ratio which defines the difference between individual Ic and the average Ic. Even only one damaged coated conductor can dramatically increase AC losses no matter which layer it locates at. The detailed AC loss distributions among coated conductors are presented and the reasons for different influences of unevenly distributed Ic as well as damaged coated conductor are discussed. [ABSTRACT FROM AUTHOR]