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This paper investigates an optimal design methodology for multiwidth (MW)high-temperature superconductor (HTS) magnets, where pancake coilswound with the narrowest tapes were placed at and near the magnet center and those with progressively wider tapes toward the top and bottom of the magnet. For a given design, target of field strength and winding bore, input parameters include tape width, number of grading tapes, and number of pancakes coils, while the main objective is to minimize the magnet volume, i.e., essentially the stored energy and thus the cost. A magnet with a single-width tape is also designed as a control sample for comparison. A case study on a design of 3-T 240-mm HTS magnet was carried out. In that case, MWmagnets save 40% wire consumption of single-width magnets. The results are expected to be beneficial to determine the practical level of HTS tape grading and estimate a volume of an MW magnet. [ABSTRACT FROM AUTHOR]

In this study, we introduce a highly accurate NMR magnetometer, which is capable of measuring the magnetic field for inhomogeneous HTS magnets. The magnetometer is based on the pulsed and Fourier-transformed NMR and 1H NMR signal analyses. The magnetometer system was fabricated according to these concepts andmagnetic field measurements on a 3THTSmagnet were carried out using various mapping paths. The test results demonstrate that the magnetometer can measure magnetic fields accurately in inhomogeneous conditions as high as approximately 864 ppm with a spherical volume of 10 mm in diameter nearly centered at the magnet center. The stronger and hence shorter RF pulse resulting from the high-power amplification enables measurements of magnetic fields in more inhomogeneous conditions. Because the permissible field homogeneity range is very wide, the magnetometer can be used for mapping fields at the preshim stage of the inhomogeneous magnets. To also verify the high-resolution performance of the magnetometer, the results are compared with measurement data obtained with a Hall magnetometer ordinarily used in such an inhomogeneity range. We expect that the proposed magnetometer will enable the precise measurements of the magnetic fields over a wide homogeneity range, and thereby bring about improvement in the shimming process of the inhomogeneous magnets. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 x 40 mm x 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. [ABSTRACT FROM AUTHOR]

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 (ξ) are investigated for the establishment of insulation design criteria of a high voltage superconducting apparatus. Dielectric experiments on gaseous nitrogen (GN2) 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 ξ 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This work aimed to study the quench behavior of a test coil assembly consisting of YBa2 Cu3 O7 -6pancake coils. Parameters such as the quench energy and the normal zone propagation velocity, which are useful in designing detection and protection systems for real-life HTS devices, have been measured. The goal is to define the limit of the applicability of commercial YBCO wire technologies, usually referred to as second generation (2G), used to wind superconducting devices. To go beyond the stability characterization, an active protection scheme has been designed, integrated to the test coil assembly and tested as well. [ABSTRACT FROM AUTHOR]

Here we suggest stable maximum temperature criteria of YBCO coated conductors (CCs) considering degradation of YBCO by repetitive exposure to excessive temperature rise. Stable maximum permissible temperature was experimentally determined as the maximum temperature at which CC does not suffer from critical current (Ic) degradation or burnout. By comparing various over-current characteristics with short-circuit characteristics in regards to the pattern of generated resistance and joule heating flux, maximum permissible temperature rise of YBCO CC in superconducting fault current limiter (SFCL) can be determined as 400 K. Our research is expected to provide rudimental basis for the temperature design of various superconducting power applications including SFCL. [ABSTRACT FROM AUTHOR]

Research on resistive superconducting fault current limiters (SFCLs) using coated conductor(CC) has now been advanced from development to commercialization stage. It is necessary to investigate the recovery characteristics of SFCL for effective application to power system. In Korea, if the SFCL is directly inserted to distribution power grid, it must be recovered in 0.5 s after fault. Since temperature sensor is not accurate in liquid. nitrogen bathe and temperature of CC, after falling down below 92 K, is impossible to be measured by electrical method, it is difficult to measure the temperature of SFCL during the recovery of YBCO CC. In this paper, an experimental method was proposed to determine the recovery of resistive SFCLs. Under over-current for 0.1 s, maximum temperature of high temperature superconductor (HTS) wire increased to 300 K; after a few seconds, recovery time was measured by increasing DC current. With these experiments, thermal relaxation time required for the temperature of CC to decrease to 77 K was analyzed. [ABSTRACT FROM AUTHOR]

In order to minimize the impedance in nominal current, non-inductive superconducting coil can be applied to SFCL. In a few former researches on the coil, the two wires connected in parallel were same. This conventional coil generates only resistive impedance during a fault. This paper proposes non-inductive coil wound with two kinds of HTS wire in parallel. Since properties of the two wires such as index number and resistance of stabilizer are considerably different from each other, current distribution between the two wires is unequal. The unequal current distribution induces difference of magnetic flux between the two windings. Hence, the proposed coil generates inductive impedance as well as resistive one. To fabricate proposed coils, three wires were used; Bi2223 tape, copper-stabilized Y123 coated conductor (CC) and stainless steel (SS)-stabilized CC. The short-circuit test of the coils were conducted to investigate the impedance characteristics. As a result, the proposed coil wound with two kinds of wire has inductive impedance. Even if the inductance was small because of short wire length, it is obvious that our proposed coil make magnetic field. The magnetic field can be applied to commutate a fast switch in hybrid SFCL systems. [ABSTRACT FROM AUTHOR]

This paper deals with the design and test of a high temperature superconducting (HTS) power supply with YBCO coated conductor (CC) pancake load, also presents its operational characteristics through experiments. HIS power supply consists of two heaters, an electromagnet, a solenoid, and a pancake load of about 0.73 mH. The solenoid and pancake load were fabricated by using YBCO CC. The timing sequential control of two heaters and an electromagnet is an important factor to generate pumping-current in the pancake load. The heat transfer analysis of heater triggering parts of the YBCO CC solenoid according to the heater input was carried out~ Based upon the analysis, the 3 A electromagnet current and the 0.55 A dc heater current were optimally derived, and 4 s, 8 s and 16 s for the pumping period were selected in this experiment. A region of the superconducting tape with a buried heating coil can be switched by means of its temperature change. In order to measure the pumping-current with respect to the magnet flux changes, a hall sensor was installed at the center of the YBCO CC pancake load. In the experiment, the maximum pumping current reached about 20 A. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study of 2-dimensional normal zone propagation (NZP) in winding pack models comprised of 12 straight YBCO tapes stacked with wet, i.e., epoxied, insulating spacers. In each winding pack, the YBCO tapes were connected electrically in series in such a way that a transport current through the YBCO tapes zigzagged from one end of the winding pack to the other end of the winding pack. An insulated heater strip placed at the middle of the stack was energized to trigger a quench in YBCO tapes with a combination of heater taps which permits the length of the heated section to be varied for 1- or 2-dimensional NZP. Voltage taps of various lengths were placed within the winding packs to measure the transverse and longitudinal NZP speeds. Measurements with wet-spacers in which a large contact thermal resistance at each YBCO tape and spacer interface is chiefly responsible for very slow transverse NZP velocities, effectively eliminate the interface thermal resistance, resulting in faster transverse NZP speeds. Numerical simulation that neglects interface thermal resistance agrees quite well with experiment. [ABSTRACT FROM AUTHOR]

This paper presents the development status of joint method between the superconducting YBCO coated conductors (YBCO CC). In general, the YBCO-CC tape consists of an upper stabilizer, substrate, buffer, YBCO and a bottom stabilizer. It is suggested that the stabilizer between the two YBCO-CC tapes need to be removed, in order to improve the characteristics of the joints. The removing process was conducted by using heat and partial etching. The resistance and critical current of the joints were measured from the V I curve. The optical micrographs were analyzed for microstructures between the joint areas. After several times of over current test, the critical currents of the various types of joint samples were examined for applying to the high temperature superconducting magnet system. [ABSTRACT FROM AUTHOR]

According to recent studies, economical feasibility of resistive superconducting fault current limiters (FCL5) in transmission and distribution power line is confirmed. Since the SFCL is operated under alternating current (AC), it causes power loss, so-called AC loss, during normal operation condition even though it is superconductor. Bifilar pancake winding with coated conductor (CC) is expected to reduce AC loss of the SFCL by canceling magnetic fields efficiently as compared with other type SFCLs using CC in the same length. AC loss characteristic of the bifilar pancake type coil for SFCL application was investigated in this paper. Two bifilar pancake coils were wound using CC with facing on high temperature superconductor (HTS) sides each other and substrate (Ni-W) sides each other, respectively. AC losses of the coils were measured at 77 K and theoretical analysis was performed by finite element method (FEM). The experimental results are compared with the Norris equations and numerical values using FEM. [ABSTRACT FROM AUTHOR]

This paper deals with an analysis on the optimum lap joint method of the YBCO coated conductor (CC) wire. Effective low resistance joint is important for the development of persistent current mode system using the second generation high temperature superconducting (2G HTS) wire, YBCO CC. CC tape is stacked with copper or stainless steel stabilizer, silver layer, YBCO layer, buffer and substrate. The joint between CCs was performed with low temperature InBi solder. YBCO samples with various contact conditions were fabricated and tested. Characteristics of jointed CC tape were evaluated from the V-I curve and contact resistance was derived from experimental results. Characteristics of jointed CC were investigated by electrical analysis and optical micrograph. The BSCCO wires were jointed at different conditions, and the results were compared with the joint between the YBCO CCs. [ABSTRACT FROM AUTHOR]

A superconducting fault current limiter (SFCL) using high temperature superconducting (HTS) wire has been developed in Korea. While the first-generation wire has difficulty in adopting various matrices because it is made by PIT process, the second-generation wire has flexibility in the design of its stabilizer. In general, coated conductor (CC) tape is clad with a thick metal layer as a stabilizer on the superconducting layer such as YBCO. In addition, the metal layer has good electrical conductivity. However, resistive SFCL, when a fault occurs, limits fault current using high resistance of the stabilizer. Therefore, the design of stabilizer is one of the most important parts in the design of SFCL. In this paper, over-current characteristics of CC tapes clad with stabilizers having various specifications were experimentally investigated. It was possible to design the stabilizer of CC based on calculation. An SFCL rated on 13.2 kV/630 A was designed using the optimal design of the stabilizer. [ABSTRACT FROM AUTHOR]

Since resistive superconducting fault current limiters (SFCLs) are inserted to a power system directly, it is necessary to recover instantly after the clearance of a fault. Most resistive SFCLs using BSCCO bulk or thick film have a recovery time of tens of seconds. An SFCL using YBCO coated conductor (CC) has a large surface area contacted to liquid nitrogen. Joule heat flux of the SFCL is smaller than that of other types when a fault occurs. Therefore, it is important for the SFCL employing CC to investigate a recovery time. In this paper, the recovery characteristics of SFCL with respect to applied voltage were analysed in a power system. All tests were performed in liquid nitrogen and sub-cooled nitrogen. From this result, the parameters for recovery time were obtained. [ABSTRACT FROM AUTHOR]

As a part of the 21st Century Frontier R&D Program in Korea being performed from 2004, a non-inductive winding type superconducting fault current limiter (SFCL) is being developed. The target of the second year in phase II of the program is to develop a 220 V/300 A class non-inductive winding type SFCL as a prototype for a 13.2 kV/630 A class, the final goal of phase II. This SFCL has three solenoid type non-inductively wound coils in series using a 2G high temperature superconducting (HTS) wire and it was tested in sub-cooled nitrogen of 65 K, 1 atm. A coil which is composed of four parallel windings in a bobbin and winding directions are opposite to have non-inductive characteristics. Three coils were connected in series and the total length of 108 m of 2G HTS wire was used. Short-circuit tests were performed at applied voltage of 220 V and the SFCL limited the fault current to a few kA extents at the tests. Recovery time of the SFCL was measured after short-circuit tests. [ABSTRACT FROM AUTHOR]

Many superconductor applications such as magnetic levitation train (MAGLEV), magnetic resonance imaging (MRI) and superconducting magnetic energy storage (SMES) must be operated on persistent current mode to eliminate loss. Research on PCS using coated conductor (CC) tape has not been actively in progress, compare with that using BSCCO tape. In this paper, current charging rate was adjusted to 0.5 A/s to investigate operating characteristics of PCS. To analyse current decay during persistent current mode, new electrical equivalent model considering the n-value of CC was applied. Experimental results were compared with the theoretical results which were derived by applying finite deference method (FDM). We concluded that the characteristics of initial current decay were determined by the voltage generated in the load due to n-value, joint resistance and current charging [ABSTRACT FROM AUTHOR]

This paper deals with the preliminary study on the HTSC persistent current switch (PCS) for MAGLEV in Korea. The onboard HTSC levitation magnet system for high-speed maglev has advantage in power consumption because it can be operated in persistent current mode (PCM). The high speed superconducting maglev operated in PCM does not need the additional electrical energy to provide levitation force. To develop the PCS having good characteristics, it is important to develop a technology to minimize the joint resistance between two superconducting wires. The HTSC levitation magnet system consists of one HTSC magnet wound with Bi-2223 wire and a persistent current switch (PCS). The inductance of the magnet was 18.5 mH and total joint resistance of the magnet was 5.74 × 10-7 Ω. The PCS was experimented with respect to various ramping-up rates and magnitudes of charging current. The experimental results were compared with simulation results using finite different method. Based on these results, the current decay of 1 H class PCS using HTSC wire was calculated. [ABSTRACT FROM AUTHOR]

In this study, a high temperature superconducting (HTS) coil is designed for a single phase 8.3 MVA fault current limiter (FCL) whose ratings are 13.2 kV in voltage and 630 A in current. The coil is wound with the bifilar winding method to limit the fault current only by resistance. The wire used in the HTS coil is YBCO coated conductor (CC) with metal stabilizer such as copper or stainless steel. In order to design the HTS FCL, the thermal and electrical analyses are performed considering the transient thermal conduction and the resistance development according to the temperature. The HTS coil is designed with a temperature limit of 300 K. The stainless steel stabilized wire is desirable than the copper stabilized wire because of the high resistance and the low temperature rise. As the design result, the total length of the wire is calculated as 2.56 km with 25 μm stainless steel stabilizer. The parallel number of wires is 8 and the quench current of the coil is approximately 1200 A at 65 K. The height and the outer diameter of the coil except the terminals and the connection parts are 0.5 m and 0.9 m, respectively. The HTS coil is composed of 7 concentric solenoid coils and each coil has 19 turns of clockwise winding and same turns of counter-clockwise winding for non-inductive property. [ABSTRACT FROM AUTHOR]

Recently, the resistive superconducting fault current limiter (SFCL) using YBCO coated conductor (CC) has been developed in many countries. Since CC has many advantages such as high n-value and high Jc compared with BSCCO tape, CC is useful to develop the resistive SFCL. The important thing for the operation of the SFCL is to reduce the AC loss like transport current loss and magnetization loss. Although the bifilarly wound magnet is a non-inductive coil, the transport current loss will certainly be produced by self-field when the AC current flows through the CC tape. A measurement of AC loss should be essential for the commercialization of the SFCL. In this paper, the transport current loss of the bifilar magnet using CC is measured by the electric method and the calorimetric method and compared with Norris equation because inductance of the bifilarly wound magnet is very small. [ABSTRACT FROM AUTHOR]

Worldwide development of superconducting power equipments by exploiting the 2G wire is continuously ongoing; moreover, superconductor wire manufacturing companies are also making constant efforts to develop superconducting power equipments for the purpose of increasing critical current density as well as improving homogeneity of the wire. Particularly, the development of resistive superconducting fault current limiter (SFCL) is making an active progress and related tests of superconducting wire are performed as well. For resistive SFCL, the superconducting wire with stainless steel stabilizer is more appropriate than that with copper since stainless steel generates more resistances per unit length than copper. Especially, AMSC in USA succeeded in developing coated conductor (CC) clad with stainless steel stabilizer. The stabilizer of 25 μm is laminated on the superconductor layer and under the substrate, both of which are electrically jointed with solder. By using the wire, the design and manufacture of resistive SFCL was performed. For the commercialization of resistive SFCL, it is one of the most key factors to decrease inductive reactance in the process of designing coils. Therefore, coils were wound by non-inductive winding method and their losses in normal condition were measured. Also, current limiting characteristics of the SFCL module wound with CC clad with stainless steel stabilizer were studied by short-circuit test. [ABSTRACT FROM AUTHOR]

This paper describes the characteristics analysis of a high-Tc superconducting (HTSC) power supply considering flux creep effect, and also presents its operational characteristics through experiments. The power supply can be employed to charge an HTSC magnet. An HTSC power supply consists of two heaters, an electromagnet, a Bi-2223 solenoid, and a series-connected Bi-2223 pancake load. The pancake load was fabricated by connecting four double pancake coils in series. In the experiments, two cases of the pumping period, which correspond to 8.5 and 17 s, were used with an electromagnet of 331 mH and a dc heater current of 0.8 A. A region of the superconducting tape with a buried heating coil can be switched by means of its temperature change. In order to measure the pumping-current with respect to the magnet flux changes, a hall sensor was installed at the center of the Bi-2223 pancake load. The experimental observations have been compared with the theoretical predictions. In this experiment, the pumping-current has reached about 22.9 A. [ABSTRACT FROM AUTHOR]

This paper deals with feasibility of fault current limiter (FCL) by using Bi-2223 high temperature superconducting (HTS) wire. The FCL using HTS wire has some advantages of stability, flexibility of structure and cost compared with existing superconducting FCLs using bulk or thin film. Even if the FCL using HTS wire has zero resistance in normal state, it needs to be wound as a bifilar winding for non inductance. In this paper, four types of FCL module with bifilar winding were suggested, manufactured and experimented with short circuit tests in 77 K. The FCL modules have different fault current limiting characteristic and stability respectively. These types of module are solenoid, pancake, solenoid impregnated with epoxy resin and pancake impregnated with epoxy resin. The FCL module was applied by controllable AC bias during fault duration, 0.1 s, from 0.5 V to 22 V. A process of fault occurrence in this test is very similar to a fault occurrence in real system. In results of tests, the pancake type was more effective to limit a fault current than the solenoid type. Also modules impregnated with epoxy resin showed more efficient current limiting characteristics than nonimpregnated modules. The solenoid type has better characteristic of stability. The feasibility of the FCL by using HTS wire was verified by this paper. [ABSTRACT FROM AUTHOR]

Superconducting fault current limiters (SFCLs) have been developed by many research groups. However, there is no standard for current limiting device. Recently, YBCO coated conductor (C.C.) which is named as 2nd-generation wire has been developed rapidly. YBCO C.C. has many advantages for applying to fault current limiting material. In this paper, a bifilar winding type SFCL was manufactured using YBCO C.C. The bifilar coil was wound as pancake type, and the length of C.C. tape used was 8 m. The short-circuit test of the SFCL was performed successfully rated on 30V/80A. The SFCL had a very low impedance in normal operation and limited the fault current effectively when a fault occurred. From the result, it could be confirmed that the bifilar winding type FCL using YBCO C.C. is feasible. Large-scale SFCL using C.C. should be developed in the future. [ABSTRACT FROM AUTHOR]

This paper deals with characteristics of a High-Tc superconductor (HTS) persistent current switch (PCS) system considering the n-value. I also present its operational characteristics through experiments. A HTS PCS system mainly consists of a PCS, a HTS magnet load, and a magnet power supply (MPS). The HTS magnet load was made-up of two double pancake coils in series. In order to measure the persistent current with respect to the magnet flux changes, a hall sensor was installed at the center of the magnet load. In the experiments, the initial current dropped rapidly in the persistent current mode. In order to analyze current decay, we introduced a new electrical equivalent model considering the n-value. Experimental results of the HTS PCS system have been compared with the theoretical results. It has been concluded that the characteristics of initial current decay were mainly determined by the voltages generated in the pancake load due to n-value and joint resistance. [ABSTRACT FROM AUTHOR]

This paper deals with the development of a 6.6 kV/ 200 A HTS magnet for inductive superconducting fault current limiter (SFCL) that uses a sub-cooled nitrogen cooling system which is expected to be very useful to the applied HTS machines. The several characteristics of the HTS magnet such as critical current, electrical insulation and heat transfer can be enhanced in the sub-cooled nitrogen cooling system rather than in saturated liquid nitrogen (LN2) cooling system. To obtain sub-cooled nitrogen, LN2 was cooled down to 64 K with GM-cryocooler and its pressure was kept at 101 kPa with gaseous helium. In this investigation, the HTS magnet for a 6.6 kV/200 A SFCL was developed and its long-run operation characteristics were measured and analyzed. The characteristics of the sub-cooled nitrogen system like temperature, level of LN2 and pressure of cryogenic system were not degraded in spite of the several over current tests, electrical insulation tests, and even long-run operation tests with rated transport current. [ABSTRACT FROM AUTHOR]

With the successful commercialization of Bi-2223 powder-in-tube wire, many attempts to the R & D of the high-Tc superconducting (HTS) magnets for high magnetic field applications are now being implemented actively. Although operating temperature of HTS magnet must be kept in the designed level, the magnetic energy and mechanical disturbance can make the operational temperature of HTS magnet unstable. Especially, generated heat energy of inner HTS winding is apt to accumulate, so the normal region appears in HTS winding. This paper deals with the quenching characteristic of reinforced Bi-2223 wire and two bare Bi-2223 wires in adiabatic condition. The minimum quench energy (MQE) of HTS wires was affected by the material and ratio of their matrix. In the same condition, the normal zone propagation (NZP) energy of nonreinforced HTS wire was smaller than that of reinforced HTS wire. [ABSTRACT FROM AUTHOR]

In general case of DC reactor type superconducting fault current limiter (SFCL), a fault current gradually increases during the fault. It takes above 5 cycles to cut off the fault in the existing power system installed the conventional circuit breakers (CBs). Therefore, the fault current increases during the fault even if the SFCL is installed. This paper proposes a technique for decaying the fault current with the function of the fault detection and control of power converter of the SFCL. Using the proposed method, the fault current can decay after 1-2 cycles when the fault occurs. To analyze this technique, three-phase 6.6 kV/200 A SFCL was fabricated. The SFCL has just one DC reactor, an AC to DC power converter which has thyristors as the rectifying device, and a three-phase transformer, which is called magnetic core reactor (MCR). The short-circuit tests of this SFCL were performed successfully. Comparing the result using the proposed technique with the typical result, the fault current is decreased effectively by the proposed technique. This result shows that this SFCL using the fault detection and control of power converter can be applied to the existing power system which has conventional CBs. [ABSTRACT FROM AUTHOR]

This paper deals with determination of equivalent circuit parameters of the Low-T[sub c] Superconducting (LTS) power supply for charging of the LTS magnet, as well as analysis of its characteristics as determined through experiments. The power supply consists of two exciters, a rotor, a stator, and an LTS magnet. In this experiment, a 25.8 mH LTS magnet was used, and rotor revolutions from 30 to 300 rpm were used. The magnetic flux distribution analysis of the system was carried out. Based upon this analysis, maximum 150 A dc excitation current was optimally derived. In order to measure the pumping-current with respect to the magnet flux changes, a hall sensor was installed at the center of the LTS magnet. The experimental observations have been compared with the theoretical predictions. In this experiment, the pumping-current has reached about 372 A. [ABSTRACT FROM AUTHOR]

High-Tc superconducting fault current limiter (SFCL) with DC reactor is the power equipment which plays the role of limiting fault currents by inductance of the DC reactor. Therefore manufacture of the DC reactor is very important part in developing this type of SFCL. The DC reactor makes use of high-T[sub c] superconducting (HTS) magnet. Because high-T[sub c] superconducting wires are rectangular tape and contain ceramic compounds, the winding method and the tension control of the HTS magnet are different from those of normal conductor magnets such as copper winding magnet. In this research, we designed and manufactured the winding machine for HTS magnets. We fabricated four HTS magnets wound with various tension. Characteristics of the fabricated magnets are observed through measurements of critical currents. This paper suggests the optimal winding method of HTS magnets. [ABSTRACT FROM AUTHOR]

Superconducting dc reactor protects power system by limiting the amplitude of fault current with its inductance. Therefore, it is very important to design and simulate the dc reactor precisely for making the power system stable and effective. In this paper, we designed the superconducting dc reactor of inductive superconducting fault current limiter conceptually and acquired the optimal design parameters by using Finite Element Method (FEM). We manufactured the superconducting dc reactor and tested its characteristics at cryocooler-cooled 20 K temperature. Moreover, compared experimental characteristics with simulation results and analyzed them. We introduced the design method of the superconducting dc reactor and the fabrication method of 1.2 kV/80 A class dc reactor for inductive superconducting fault current limiter. Finally, we performed the short circuit test and discussed the results. [ABSTRACT FROM AUTHOR]

In this paper, characteristics of a heater-triggered switching system for the charging of Bi-2223 double pancake load with 1.7 mit has been analyzed through the simulations and experiments. Two heaters were used to store the energy in high-T[sub c] superconducting (HTS) load. The timing of the sequential control and the heating current with two heaters are important factors to generate pumping-current. The thermal analysis of the switch considering the heater input and time was carried out. Based on the analysis just mentioned, heater-triggered switch was fabricated. Characteristic analysis was carried out through two modes having different sequential timing controls. Maximum current stored in the IIIS load reached 18 A and the pumping rate was 113 mA/s at that time. [ABSTRACT FROM AUTHOR]

To develop DC reactor type Superconducting Fault Current Limiter (SFCL), the most important elements are superconducting magnets or inductors. Recently large size magnets have been developed, according as the improvement of high temperature superconducting wire. In DC reactor type SFCL, the purpose of magnet is to store generated electric energy of power system immediately after fault. Therefore most of inductors are designed with air core since magnetic core inductor is too easy saturated to absorb the energy. Therefore the inductor consumes so much superconducting wire to make large inductance and these expensive coils are weak point of DC reactor type SFCL. To solve this problem, Reverse Magnetization Bias (RMB) method is introduced. The energy capacity of magnetic core is expanded to several times. With the shorter length of HTC superconducting wire, the more good effect was obtained in 40V prototype SFCL. [ABSTRACT FROM AUTHOR]

Examines the operational characteristics of low temperature superconducting power supplies. Series-parallel connections of superconducting circuits; Current pumping rate of the circuits; Rotational magnetic flux.

Examines the design, fabrication and characteristics of high temperature superconducting power supply. Components of the power supply; Principles of operation; Timing sequence control; Maximum pumping current.

Investigates the design and fabrication of a high critical-temperature superconducting (HTSC) power supply with the bismuth-2223 pancake load. Pumping current of the HTSC with respect to magnet flux change; Use of the superconducting switch for heater-trigger.

Reports on the operational characteristics of discrete-sheet type low-critical temperature superconducting (LTS) power supply. Comparison between continuous-sheet type LTS power supply and discrete-sheet type LTS power supply; Maximum pumping-current; LTS power supply concept; Electrical parameters.