-
-
[show abstract]
[hide abstract]
ABSTRACT: Recently, the smart fault current controller (FCC) was proposed in order to apply to the smart grid. The smart FCC consists of an HTS coil, an AC/DC rectifier, and a control unit. A fault current should be immediately limited by the inductance of the coil at the first peak, and then adjusted by controlling the rectifier. The larger inductance of the coil induces the lower fault current. However, a large inductance coil requires high cost and large size. To reduce the HTS conductor consumption, an HTS coil with a reversely magnetized core (RMC) was proposed. To verify the concept, two permanent magnets were installed. In this paper, various model coils were fabricated and applied to the FCC system: 1) air core, 2) open iron core, 3) closed iron core, 4) open core with RMC, and 5) closed core with RMC. Based on a comparative study on the five models, an HTS coil with a closed RMC has the lowest first peak current. The first peak current in the proposed model was 27.8% smaller than that of air core case. The experimental results show that the proposed concept is to reduce the wire consumption.
IEEE Transactions on Applied Superconductivity - IEEE TRANS APPL SUPERCONDUCT. 01/2012; 22(3):5601905-5601905.
-
[show abstract]
[hide abstract]
ABSTRACT: 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.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A non-inductive coil is an essential element of a resistive superconducting fault current limiter (FCL). A bifilar pancake type non-inductive coil, which is most common type, has two drawbacks; difficulty of paralleling tapes and a high risk of electrical breakdown at the terminal part. Although the bifilar type is simple as an element, large-scale FCL needs quite a number of series and parallel connections between elements. To make a non-inductive coil using conventional inductive elementary coils, we propose a novel structure of the coil. It looks like a toroid but entire inductance is near zero. This coil can overcome the drawbacks of conventional bifilar coil. In this paper, we confirm the new concept by numerical analyses. A few kinds of new models are compared, and then we concluded the proposed toroidal shape one is most suitable. This new structure coil can help implement of a hybrid FCL which is to generate the magnetic field at only fault.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In general, the stabilizer of a ReBCO-coated conductor (CC) plays a very important role in bypassing and transferring the excessive heat when quench occurs. For an optimal design, selecting the appropriate materials and stabilizer thickness is an important issue for enhancing the thermal/electrical stability of superconducting power devices. This study examined the electrical and thermal behavior of GdBCO CC tape in terms of the stabilizer thickness as well as the effects of variations of the Ag stabilizer thickness on the thermal/electrical stability through an over-current test. An electroplating technique was employed to obtain a Ag stabilizer with various thicknesses without serious degradation of the superconducting properties.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: High-Tc superconducting (HTS) wires have showed good capabilities as an alternative conductor for superconducting magnet. The HTS wires have more current carrying capability within high external magnetic field and its stability against external disturbance is much higher than the low temperature superconducting (LTS) wires. But the HTS wire has slower normal zone propagation (NZP) velocity which makes HTS magnets hard to be protected from unexpected hot spot. This paper presents experimental test and numerical analysis about the relation between transport current and rate of temperature rise in a hot spot. A sample which contained a HTS wire, a heater, and temperature sensor was fabricated and an experimental test on measuring normal zone propagation and temperature of the HTS wire was conducted. A numerical model was also built to estimate transient temperature rise of a winding pack model which was representing practical winding of HTS magnets. The numerical model and its numerical estimation results are expected to be a guideline about designing proper protection technique and operating current for HTS magnets.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A simultaneous quench has been one of challenging issues in a development of a superconducting fault current limiter (SFCL) as long as series-connected superconducting materials are not identical each other. This paper deals with a parameter determination of a condition for simultaneous quench in series-connected YBCO coated conductors (CC), as a preliminary step to develop its faculties for high voltage CC applications. An electrical and thermal analysis based on the finite element method (FEM) showed that decisive parameters were critical current and n-value. For verifying the analysis, two sets of series-connected samples from a batch of AMSC 344S, which is clad on stainless steel, were short-circuit tested. One set has quite different critical current, whereas the other similar ones. The analysis estimated the quench initiation characteristics among the samples in both cases. After the verification, the condition for simultaneous quench, i.e. allowable deviation of critical current and n-value, has been obtained.
IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Electrical and thermal characteristics of a high-Tc superconducting (HTS) tape have close relation to a performance of a resistive type superconducting fault current limiter (SFCL). When an HTS coated conductor (CC) is applied to the SFCL, because the CC is a composite conductor, dimensions and material properties including electrical resistivity, thermal conductivity, and volumetric heat capacity of substrate, silver layer, YBCO, and stabilizer of the CC will affect to the fault current limiting performance and recovery time. This paper presents experimental results about fault current test of commercialized CCs to evaluate their compatibilities for resistive SFCLs and a numerical analysis using finite element method to design an HTS conductor for the SFCLs. The results from the analytical models of the CCs were compared to the experimental results. An HTS tape which is more suitable for the resistive type SFCLs was proposed as a conclusion.
IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A resistive superconducting fault current limiter (SFCL) has two drawbacks-relatively higher impedance and longer recovery time than the requirement of the electric power system. A parallel-connected bypass reactor (BPR) can be a solution to both problems. As a stage of proof-of-concept, an SFCL comprised of an YBCO S/N switch and a Bi2223-BPR had been presented in the former paper. Although the previous one has shorter recovery time, the generated impedance after a fault was too low to satisfy the requirement of the power system. To apply the SFCL into the power system, the SFCL has proper impedance during the fault. Therefore, we proposed bypass reactors to achieve higher impedance than the previous one in this paper. The SFCLs with a bypass reactor were fabricated and short-circuit test with the SFCLs were conducted. The test results were compared in point of current limiting characteristics and recovery. This research would be applied to a conceptual design of BPR.
IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A Hybrid fault current limiter (FCL) proposed by our group previously is composed of a superconducting coil, a fast switch and a bypass reactor. The superconducting coil wound with two kinds of HTS wire has zero impedance when normal current flows in the coil. However, different quench characteristics of the HTS wire generate magnetic flux in the coil when fault current flows in the coil. As a result, the fast switch was opened by the repulsive force applied to the aluminum plate above the coil. In previous studies, our group verified operating characteristics and feasibility of the fast switch. In this paper, comparison of pancake type and solenoid type non-inductive coil wound with two kinds of the HTS wire was performed by using short-circuit test and finite element method. From these results, short-circuit characteristic of a coil can be acquired and magnitude of the repulsive force and magnetic field can be analysed.
IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents the characteristic analysis on the high-Tc superconducting (HTS) electrodynamic suspension (EDS) simulator. In EDS maglev trains, the relative velocity between the moving high field magnet and the fixed ground conductor makes the magnetic reaction between two components. The magnetic reaction generates the levitation force of the EDS system. The distribution of the magnetic flux on the ground conductor affects the strength of the levitation force. A EDS simulator basically consists of levitation magnet and ground conductor and one of these component should be a moving part. In the static type EDS simulator, the levitation force is generated by the velocity equivalent AC current. Therefore, the static type EDS simulator does not need the high speed moving parts and can test the effect of the variations of the ground conductors easily by the change of the frequency of the applying AC current. To design the static type simulator optimally, the HTS levitation magnet and the characteristics of the EDS system were numerically analysed by 3-D finite element method (FEM). Based on the numerical analysis, the static type EDS simulator was designed manufactured and tested. The simulator consists of an HTS magnet, the fixed ground conductor(s), an AC power supply, resonating components, force measuring devices, and a supporting structure. From the calculation and test results on this paper, the consideration of the magnetic flux distribution according to the levitation height should be included in the process of the ground conductor design.
IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A sub-cooled liquid nitrogen system is known to be a promising method to develop a high voltage superconducting magnet. Therefore, the investigation of dielectric characteristics of gaseous electrical insulation media is important for the design of a high voltage superconducting apparatus. In this paper, dielectric characteristics of various gases according to utilization factors are investigated for the establishment of insulation design criteria of a high voltage superconducting apparatus. Dielectric experiments on gaseous nitrogen and gaseous helium (GHe) are carried out by using several kinds of sphere-to-plane electrode systems made of stainless steel. As a result, it is found that the dielectric characteristics of gas are determined by as well as gap length of electrode systems. Also, empirical expressions for electrical breakdown performance of gaseous electrical insulation media are derived and formulated. It is considered that the results of the study would be applicable to designing a high voltage superconducting apparatus.
IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents experimental and analytical results of trapped field characteristics of a stack of square YBCO thin film plates for compact NMR magnets. Each YBCO plate, 40 mm ?? 40 mm ?? 0.08 mm, has a 25-mm diameter hole at its center. A total of 500 stacked plates were used to build a 40-mm long magnet. Its trapped field, in a bath of liquid nitrogen, was measured for spatial field distribution and temporal stability. Comparison of measured and analytical results is presented: the effects on trapped field characteristics of the unsaturated nickel substrate and the non-uniform current distribution in the YBCO plate are discussed.
IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents experimental and analytical results of trapped field characteristics of a stack of square YBCO thin film plates for compact NMR magnets. Each YBCO plate, 40 mm × 40 mm × 0.08 mm, has a 25-mm diameter hole at its center. A total of 500 stacked plates were used to build a 40-mm long magnet. Its trapped field, in a bath of liquid nitrogen, was measured for spatial field distribution and temporal stability. Comparison of measured and analytical results is presented: the effects on trapped field characteristics of the unsaturated nickel substrate and the non-uniform current distribution in the YBCO plate are discussed.
IEEE transactions on applied superconductivity : a publication of the IEEE Superconductivity Committee. 06/2010; 20(3):1037-1040.
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents experimental and simulation results of a screening current induced magnetic field (SCF) in a high temperature superconductor (HTS) insert that constitutes a low-/high-temperature superconductor (LTS/HTS) NMR magnet. In this experiment, the HTS insert, a stack of 50 double-pancake coils, each wound with Bi2223 tape, was operated at 77 K. A screening current was induced in the HTS insert by three magnetic field sources: 1) a self field from the HTS insert; 2) an external field from a 5-T background magnet; and 3) combinations of 1) and 2). For each field excitation, which induced an SCF, its axial field distribution and temporal variations were measured and compared with simulation results based on the critical state model. Agreement on field profile between experiment and simulation is satisfactory but more work is needed to make the simulation useful for designing shim coils that will cancel the SCF.
IEEE transactions on applied superconductivity : a publication of the IEEE Superconductivity Committee. 07/2009; 19(3):2269-2272.
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents experimental and simulation results of a screening current induced magnetic field (SCF) in a high temperature superconductor (HTS) insert that constitutes a low-/high-temperature superconductor (LTS/HTS) NMR magnet. In this experiment, the HTS insert, a stack of 50 double-pancake coils, each wound with Bi2223 tape, was operated at 77 K. A screening current was induced in the HTS insert by three magnetic field sources: 1) a self field from the HTS insert; 2) an external field from a 5-T background magnet; and 3) combinations of 1) and 2). For each field excitation, which induced an SCF, its axial field distribution and temporal variations were measured and compared with simulation results based on the critical state model. Agreement on field profile between experiment and simulation is satisfactory but more work is needed to make the simulation useful for designing shim coils that will cancel the SCF.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper addresses adverse effects of dimensional uncertainties of an HTS insert assembled with double-pancake coils on spatial field homogeneity. Each DP coil was wound with Bi2223 tapes having dimensional tolerances larger than one order of magnitude of those accepted for LTS wires used in conventional NMR magnets. The paper presents: 1) dimensional variations measured in two LTS/HTS NMR magnets, 350 MHz (LH350) and 700 MHz (LH700), both built and operated at the Francis Bitter Magnet Laboratory; and 2) an analytical technique and its application to elucidate the field impurities measured with the two LTS/HTS magnets. Field impurities computed with the analytical model and those measured with the two LTS/HTS magnets agree quite well, demonstrating that this analytical technique is applicable to design a DP-assembled HTS insert with an improved field homogeneity for a high-field LTS/HTS NMR magnet.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper deals with design and operating test of a novel hybrid FCL. The FCL system consists of a coil, a fast switch and a resistor for bypassing the fault current. The switch is driven by novel non-inductive coil suggested in this paper but an extra driving coil is required for fast switch in existing hybrid FCL. We used two kinds of HTS wire for the coil. The impedance of the coil was negligible in normal operation. But different quench characteristics of HTS wires caused asymmetric current distribution which induced effective magnetic flux in the coil during faults. The switch was opened by repulsive force from this magnetic flux in fast response to the fault. Then, all current were flew through the normal conductive bypass resistor connected in parallel to both the coil and the switch. Electromagnetic analysis of the coil based on finite element method was performed. Also, a small-scale asymmetric non-inductive coil was designed, fabricated and tested. The proposed hybrid FCL system showed fast and efficient current limiting characteristic.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper reports results, experimental and analytical, of the nonlinear behavior of a shim coil in the presence of an HTS coil assembled with double-pancake (DP) HTS-tape coils. The experimental results are from: 1) operation of a 700 MHz LTS/HTS NMR magnet (LH700) consisting of a 600 MHz LTS NMR magnet (L600) equipped with superconducting shim coils and a 100 MHz DP-assembled HTS insert (H100) and; 2) an experiment with a room-temperature (RT) Z1 shim coil coupled to a 50 MHz DP-as-sembled HTS insert (H50). A field mapping theory with a harmonic analysis is applied to interpret both results. Based on experimental results and analyses, we conclude that the screening-current-induced field (SCF) generated by a DP-assembled HTS insert is primarily responsible for the nonlinear behavior, including strength degradation, of a shim coil.
IEEE transactions on applied superconductivity : a publication of the IEEE Superconductivity Committee. 06/2009; 19(3):2285-2288.
-
[show abstract]
[hide abstract]
ABSTRACT: This paper addresses adverse effects of dimensional uncertainties of an HTS insert assembled with double-pancake coils on spatial field homogeneity. Each DP coil was wound with Bi2223 tapes having dimensional tolerances larger than one order of magnitude of those accepted for LTS wires used in conventional NMR magnets. The paper presents: 1) dimensional variations measured in two LTS/HTS NMR magnets, 350 MHz (LH350) and 700 MHz (LH700), both built and operated at the Francis Bitter Magnet Laboratory; and 2) an analytical technique and its application to elucidate the field impurities measured with the two LTS/HTS magnets. Field impurities computed with the analytical model and those measured with the two LTS/HTS magnets agree quite well, demonstrating that this analytical technique is applicable to design a DP-assembled HTS insert with an improved field homogeneity for a high-field LTS/HTS NMR magnet.
IEEE transactions on applied superconductivity : a publication of the IEEE Superconductivity Committee. 06/2009; 19(3):2281-2284.
