Search

• SFCL make the electric grids more resilient. • REBCO tapes suit well for SFCL. • SFCL has clearly matured for use in electric grids. • Current Flow Diverter (CFD) concept still improve the robustness of operation. • Sapphire substrate tape could be a breakthrough for SFCL. High Temperature Superconductors (HTS) made the Superconducting Fault Current Limiter (SFCL) a reality in power electric grids. Resistive SFCL, which is the subject of this article, is based on a unique property of superconductors to quench from a non-dissipative to a high dissipative state above a given current. SFCL is an attractive response to the poorly solved problem of fault currents in power electric grids and makes it possible to enhance the security and quality of electricity, something that matters more than ever. Liquid nitrogen cryogenics – which is possible thanks to HTS- makes the cryogenics user friendly. In-field SFCL operations confirm this. Second generation (2 G) HTS materials or Coated Conductors suit well to SFCL. Due to its high interest, SFCL has been the subject of a great deal of research and development. In terms of Technology Readiness Level (TRL) it reaches 8 with several in grid test experiences. Here a short history of SFCL is presented with a highlight about Curl 10, Ampacity and SuperOx devices. The two major locations in the grid are reported: grid coupling and feeder protection. The quench phenomena is described in a bit more detail before the basic design (length and cross section) is presented. The design is primarily thermal, considering two extreme operations: fault with very high prospective current (clear short-circuit) and fault with prospective current close to the minimum runaway current along the length. This operation is called the hot spot one. It is due to the intrinsic variation of the critical current along the length and to the low Normal Zone Propagation Velocity (NZPV). The cost of the superconducting conductor is given, showing no bottleneck for an economic development. All the more it is still possible to lower the cost with some developments. This article ends with two real advances presently underway: Current Flow Diverter (CFD) and Sapphire substrate superconducting 2 G tape. CFD aims to increase the NZPV, to still further secure the operation and to reduce the conductor cross section. The use of sapphire substrates allows to reduce significantly the length of the design. [ABSTRACT FROM AUTHOR]

• Critical currents depends on the rugosity percentage of the sample. • An analytical dependence of the critical currents on the rugosity is found. • Vortex-anti-vortex annihilations process depends on the value of the rugosity. We study the superconducting state of a thin film at zero external applied magnetic field under a transport electric current, J a. By taking into account the roughness percentage of its surface R , we show that the value of J a = J c 1 at which the first vortex-antivortex (V-Av) pair penetrates the sample, the superconducting-normal transition current J a = J c 2 , as well as their average velocities and dynamics, strongly depend on the R values. It will be shown that J c 1 and J c 2 follows a scaling law for different values of R. Our investigation was carried out by numerically solving the two-dimensional generalized time-dependent Ginzburg-Landau equations. [ABSTRACT FROM AUTHOR]

We have verified the influence of quantum phase transition on spin transport in the spin-1 two-dimensional XY model on the square lattice, with easy plane, single ion and exchange anisotropy. We analyze the effect of the phase transition from the Néel phase to the paramagnetic phase on the AC spin conductivity. Our results show a bit influence of the quantum phase transition on the conductivity. We also obtain a conventional spin transport for ω  > 0 and an ideal spin transport in the limit of DC conductivity and therefore, a superfluid spin transport for the DC current in this limit. We have made the diagrammatic expansion for the Green-function with objective to include the effect exciton–exciton scattering on the results. [ABSTRACT FROM AUTHOR]

The general problem of a center crack in a long cylindrical superconductor with inhomogeneous critical-current distribution is studied based on the extended Bean model for zero-field cooling (ZFC) and field cooling (FC) magnetization processes, in which the inhomogeneous parameter η is introduced for characterizing the critical-current density distribution in inhomogeneous superconductor. The effect of the inhomogeneous parameter η on both the magnetic field distribution and the variations of the normalized stress intensity factors is also obtained based on the plane strain approach and J-integral theory. The numerical results indicate that the exponential distribution of critical-current density will lead a larger trapped field inside the inhomogeneous superconductor and cause the center of the cylinder to fracture more easily. In addition, it is worth pointing out that the nonlinear field distribution is unique to the Bean model by comparing the curve shapes of the magnetization loop with homogeneous and inhomogeneous critical-current distribution. [ABSTRACT FROM AUTHOR]

A new method for calculating AC loss of two-layer SC power transmission cables using the commercial software Comsol Multiphysics, relying on the approach of the equal partition of current between the layers is proposed. Applying the method to calculate the AC-loss in a cable composed of two coaxial cylindrical SC tubes, the results are in good agreement with the analytical ones of duoblock model. Applying the method to calculate the AC-losses of a cable composed of a cylindrical copper former, surrounded by two coaxial cylindrical layers of superconducting tapes embedded in an insulating medium with tape-on-tape and tape-on-gap configurations are compared. A good agreement between the duoblock model and the numerical results for the tape-on-gap cable is observed. [ABSTRACT FROM AUTHOR]

Structural and transport properties of high performance SmBa 2 Cu 3 O 7− x coated conductors produced by a dual-chamber co-evaporation are presented. The 5 μm-thick SmBCO coated conductors grown on IBAD-MgO based Hastelloy metal templates show critical currents larger than 1020–1560 A/cm at 77 K and self-field. The current transport characteristics of the conductors are investigated by room-temperature thermoelectric microscopy and low-temperature bolometric microscopy. The local thermoelectric images show the tilted grains, grain boundaries, and microstructural defects on the surface of the coated conductors. The bias current-dependent bolometric response at low temperature displays the current of the local flux flow dissipation as an increasing bias. Furthermore, we measured micro-Raman scattering microscopic imaging on oxygen-related peaks of the conductors. Comparing the Raman signal images with the low temperature optical scanning maps, it is remarkable that the structural disorders represented by oxygen-related Raman peaks are closely related to the low temperature bolometric abnormalities. From this result, a nature of the dissipative current distribution in coated conductors is revealed. The scanning optical microscopic study will provide a promising method for quality assurance of coated conductors. [ABSTRACT FROM AUTHOR]

In two-gap superconducting thin film, there are two kinds of pancake vortices: one is arisen from the vortex in the super-current of band I (it has greater gap) and the screening electrical current; another is arisen from the vortex in the super-current of band II and the screening electrical current. In London approximation, both carry fractional quantum magnetic flux ϕ 01 and ϕ 02 respectively. Except the change of the superconducting condensation energy in the region of pancake vortex, the energy of the pancake vortices include the magnetic energy and the Josephson type coupling energy between the Cooper pair of band I and II. Because the inter-bands Josephson coupling energy is infinite increase with the size of the film, the fractional magnetic flux cannot appear alone except in the boundary regions. The element for the investigation of the vortex in two-gap superconducting thin film is the pairs (I,s) + (II,s) and the pairs (II,+1) + (II,−1). We have discussed the magnetic interaction, the Josephson coupling interactions and the structure character of these pairs in this paper. [ABSTRACT FROM AUTHOR]

A two-band superconducting fermion system is investigated. Apart from an on-site two-fermion attraction acting in the wider band an on-site four-fermion attraction is introduced. The four-fermion potential binds four electrons from both of the bands residing on a lattice site into a fermion quartet. Additionally, the local Coulomb repulsion is involved in the narrower band. There exist two order parameters in the system: a conventional BCS-type gap and a quartet one. The ground state properties such as the dependence of these order parameters on the Coulomb repulsion and the four-fermion attraction are examined. Furthermore, the average numbers of electrons constituting the system as functions of the interactions are displayed as well. It is shown that quartet superconductivity is very sensitive to the Coulomb repulsion and when subject to this interaction quartets disappear for quite small values of that. Finally, the response to an external magnetic field is studied. This reveals a quite complicated behavior of the system because in general two electric currents can flow through a specimen but there exist conditions under which one of them disappears. Such a behavior is determined by the dependence of both currents on the strength of the Coulomb repulsion and the four-fermion attraction. Two scenarios with d x 2 - y 2 -wave pairing are investigated on an initial stage as well. [ABSTRACT FROM AUTHOR]

The magnetic drug delivery system (MDDS) is a key technology to reduce the side effects in the medical applications, and the magnetic force control is a very important issue in MDDS. In general, the high magnetic field along the axial direction and high magnetic field gradient along the longitudinal direction are very useful for MDDS. So, we proposed the new magnetic force control system that consists of superconducting magnet, high temperature superconductors (HTS) bulks or tapes and ferromagnetic substances. In this new system, the shielding currents in HTS bulks and tapes due to diamagnetism of the superconductor generate the magnetic field with same direction of external magnetic field, and we can control the magnetic field gradient along the longitudinal direction by the arrangement of the HTS bulks, tapes and ferromagnetic substances. In this study, the stacked GdBCO tapes without stabilizer were used in experiments and electromagnetic analysis based on finite element method (FEM) was carried out to optimize the arrangement of the superconductors and the irons. It was confirmed that the control of magnetic field gradient along the longitudinal direction was possible by arranging the HTS bulks, tapes and irons on the superconducting magnet and then it was possible to obtain a magnetic field higher than the external field. [ABSTRACT FROM AUTHOR]

Direct detection of magnetic fields generated by the ion currents in electrolytic cells was performed and the ion currents were mapped during a cyclic voltammetry experiment. A high-Tc superconducting quantum interference device (SQUID) gradiometer with ramp-edge Josephson junctions was used as the detector and thus the first derivative of the magnetic field along the electrolytic cell surface was obtained. The electric potential vs. the reference electrode was measured between −0.3 V and 0.8 V and the hysteresis signals caused by the redox reactions of the electrolyte were observed. The vector component of the ion current during cyclic voltammetry was mapped along the electrolytic cell. As a demonstration of visualization of ion transportation, the magnetic signal was also measured at various positions above the electrolytic cell surface. [ABSTRACT FROM AUTHOR]

A quantum electric current standard is the last missing piece of the quantum metrology triangle. A suitable candidate for realizing this quantum current standard is a single-electron pumping device based on a superconductor/insulator/normal metal/insulator/superconductor (SINIS) turnstile. Here, we show the temperature dependence of the single-electron pumped current of a SINIS turnstile. As the operating temperatures are increased, the current plateaus of the single-electron pumping tilt because of increased back tunneling, which originates from the thermal broadening of energy levels in the normal metal island of the SINIS turnstile. Hence, we find that to use a SINIS turnstile for the current standard at more than 300 mK, it is necessary to increase the superconducting energy gaps of the lead material and the charging energy of the island. [ABSTRACT FROM AUTHOR]

We have evaluated magnetic field penetrations into commercial Bi2223 wires fabricated by high-pressure sintering process. Magneto-optical imaging with high-spatial resolution has been applied for that purpose. It is found that there are inhomogeneous couplings between filaments, which can lead to inhomogeneous and complicated current flow in the wire. We also found defects running oblique to the filaments, possibly created during the rolling process of the wire. [ABSTRACT FROM AUTHOR]

We performed yield analysis of large-scale adiabatic-quantum-flux-parametron (AQFP) circuits using circuit simulations based on the Monte Carlo method assuming the distribution of the critical current of Josephson junctions. Based on the simulation results, we also made an analytical model for the circuit yield of large-scale AQFP circuits. The yield analysis indicates that AQFP integrated circuits containing 1 million gates can be realized when the interconnect inductance is about 40 pH and the normalized standard deviation of the critical current is less than 1%. [ABSTRACT FROM AUTHOR]

Highlights: [•] Vortex located in a bank of a planar Josephson junction changes its character. [•] Vortex located at some discreet positions in thin strip bank suppresses to zero the zero-field current. [•] The number of these positions is equal to the number of vortices trapped. [•] Critical current-field patterns are strongly affected by the vortex position. [Copyright &y& Elsevier]

Highlights: [•] We reveal the mechanism of “self-healing” effect of uninsulated REBCO coils. [•] Uninsulated REBCO pancake coil shows “self-healing” from thermal runaway. [•] Current mode transition from “multi-turn” mode to “single-turn” triggers this effect. [Copyright &y& Elsevier]

Highlights: [•] Influences of the current sweep rate on the I–V and V–t curves are investigated. [•] Significant voltages jumps including increase and drop are observed. [•] With an increase of magnetic field, the maximum voltage increases. [ABSTRACT FROM AUTHOR]

Highlights: [•] An optimized design of HTS binary current leads is proposed. [•] Temperature distributions of two different current leads are calculated. [•] Experiments are done to certify the calculated temperature distributions. [•] The experiments proved that the copper wires increase security margins. [ABSTRACT FROM AUTHOR]

Highlights: [•] The current lead with multi-contact connector in the joint was fabricated for performance test. [•] The electrical contact resistance in the joint was measured during magnet charging. [•] The resistances of the joint were 0.4–0.9mΩ for 40–80K. [•] The heat generation due to electrical contact resistance was reduced below 1W by multiple spring louvers. [ABSTRACT FROM AUTHOR]

Highlights: [•] The superconducting element reduced only the peak value of initial fault current. [•] The normal conductivity element limited the fault current after switching operation. [•] The burden of the superconducting element was significantly reduced. [•] The normal conductivity element performed current limiting operation stably. [ABSTRACT FROM AUTHOR]

Highlights: [•] The critical current is measured for a three-layer BSCCO stacked conductor. [•] The critical current strongly depends on the current feeding mode. [•] Opposite-direction feeding mode leads to 50% increase of the critical current. [•] Current feeding mode effect implies onto a manufacture of a flexible DC power cable. [ABSTRACT FROM AUTHOR]

Highlights: [•] The electrical conductivity of PPLP in LN2 was successfully measured. [•] Based on the measured value of PPLP, DC field analysis was performed. [•] The electric field distribution was altered according to the DC applying stages. [•] The maximum electric field was observed during polarity reversal situation. [•] DC field analysis is important to determine the optimum design of DC HTS devices. [ABSTRACT FROM AUTHOR]

Highlights: [•] The loss energy density with ripple current is numerically calculated. [•] Irie–Yamafuji model is used for magnetic field dependence of critical current. [•] Calculated result of cylindrical superconductor agrees with theoretical result. [•] AC loss of strip superconductor becomes large at small ripple current amplitude. [•] Strip superconductor should be used as a form of hollow cylinder to reduce AC loss. [ABSTRACT FROM AUTHOR]

Highlights: [•] The virtual voltage method is an accurate method for an HTS film with cracks. [•] If any part of a crack is just below a coil, the inductive method will be inaccurate. [•] A crack detection method is proposed on the basis of the inductive method. [•] Both shape and position of a crack in an HTS film can be accurately determined. [ABSTRACT FROM AUTHOR]

Abstract: Dynamical behaviour of Josephson and pancake vortices (JVs and PVs) in intrinsic Josephson junctions of Bi2Sr2CaCu2O8+ y (Bi-2212) single crystal with a nano-size hole-array has been studied to measure the flow-resistance of the vortices. In the magnetic field perpendicular to the superconducting layers, flow resistance of PVs measured with the in-plane current shows a matching behaviour as usually observed at the matching fields. After the measurements, the sample was fabricated into the in-line shaped structure for the c-axis current measurements to obtain the JV flow-resistance. Instead of the usually-observed lock-in phenomenon of JVs in Bi-2212, several peaks are observed with changing the angle from the in-plane magnetic field to show the enhancement of the flow-resistance at some typical angles. When PVs are introduced into the sample with changing the angle, are trapped into holes, and are interacted with JVs, it is clearly seen that the well-aligned PVs cause the enhancement of the JV flow-resistance. [Copyright &y& Elsevier]

Highlights: [•] We develop an improved scheme for the intrinsic mechanism in TARSIS. [•] Microscopic transport map characterizing the inter-filament transfer is given. [•] V–I characteristic within a wide resistive range is revealed. [•] These results are helpful for future strand experimental design. [Copyright &y& Elsevier]

Highlights: [•] We aim to study the influence of the Josephson current passing through a d-wave S/I/S gapped graphene-based junction. [•] We investigate how the Andreev bound states and the Josephson current are affected by characteristic of d-wave pairing asymmetry. [•] It is shown that the Josephson current for special range of phase vanishes and the position of the maximum current depends on the mass gap of graphene. [Copyright &y& Elsevier]

Abstract: The high temperature superconducting (HTS) coils have very low normal zone propagation velocity (NZPV) and complicated quench behaviors. Because of these reasons, it is difficult to expect the self-protection. In this paper, two methods are suggested to improve the self-protection ability of HTS coils. One is to remove the insulation between turn–turn winding in HTS coils to enhance the thermal and electrical contacts along transverse direction and to increase the whole thermal stability of them. The other is Cu or Brass tapes are wound with HTS tape wire instead of the insulation to improve the thermal, electrical and mechanical stability of the HTS coils. To clarify the quench behaviors of the suggested coils, the normal zone propagation properties of the fabricated non-insulated HTS pancake coils were shown by measured voltage and temperature traces during the quench as a function of the operating temperature. And the characteristics of the normal transition and amount of the shared current to adjacent layers were quantitatively measured by a Hall sensor located at the center of HTS coils to measure the change of the self-magnetic field by operating current. The current sharing behaviors in the non-insulated HTS coil and the coil with Cu tape inserted were observed. The minimum quench energy (MQE) of the HTS coil with Cu tape inserted was the largest in the tested coils. It means that the HTS coil with Cu tape inserted had the highest transient stability against the thermal disturbances among the tested coils and the improvement of self protection abilities was proved. [Copyright &y& Elsevier]

Abstract: In recent years, properties of high temperature superconducting (HTS) tapes, especially in-field performance and mechanical strength, have been continuously improved. The HTS tapes have been widely used for high field (>20T) magnet researches and there are several technical challenges including field attenuation of an HTS magnet by screening currents induced within the HTS tapes. Several publications reported that the screening currents, induced by penetration of self magnetic fields into HTS tapes within an HTS magnet, weakened a field constant of the HTS magnet. The result may demonstrate that the screening current changes an overall current density distribution in HTS tapes and, as a consequence, the generated magnetic field. Therefore, it is necessary to investigate the screening current distribution in an HTS tape. This paper reports numerical simulation of the screening current distribution in an HTS tape of high field magnets using 2D finite element method with the E–J characteristic of the HTS tape taken into account. Self magnetic field distribution and its orientation to the HTS tape are also considered to compute critical currents and locally generated electric fields, two key components to figure out the distribution of screening currents. [Copyright &y& Elsevier]

Abstract: We fabricated and tested a 5T-class conduction-cooled high-temperature superconducting (HTS) coil composed of a stack of 12 single pancake coils wound with YBCO-coated conductors. The length of each single pancake coil was 25m, and the inner diameter of the coil was 50mm. The voltage–current characteristics were measured in liquid nitrogen and under conduction-cooled conditions at 10–60K. At 10K, the central magnetic field of the 12 stacked pancake coils was as high as 5.1T at 305A. We also tested the coil operation in a 4T background magnetic field. [Copyright &y& Elsevier]

Abstract: In this paper, the transformer type superconducting fault current limiter (SFCL) with two triggering current levels was suggested and its current limiting characteristics were analyzed. The structure of the suggested transformer type SFCL with two triggering current levels largely consists of two parts. One is the transformer with two magnetically coupled coils, which correspond to the primary winding and the secondary one connected with one high-T C superconducting (HTSC) element. The other is third coil, or, another secondary winding with one HTSC element, which is wound on the same iron core together with two coils. This suggested transformer type SFCL can limit the fault current by generating its limiting impedance with two different amplitudes, which are dependent on the initial amplitude of the fault current in case of the fault occurrence. To confirm the usefulness of the proposed SFCL, the current limiting tests of the SFCL according to the fault angle, one of the effective fault conditions to affect the amplitude of the initial fault current, were carried out and its effective limiting operations were discussed. [Copyright &y& Elsevier]

Abstract: The expression for the Josephson current flowing through the rectangular junctions was averaged over the values determining its properties in the case when magnetic field is less then first critical magnetic field of superconducting grains. The averaging results permit to explain the earlier performed experimental investigations of the scaling properties of critical state in random 3-d Josephson net created by transport current. At low magnetic field the average Josephson current is a quadratic function of the magnetic field and at high field the average current is an inverse quadratic function. [Copyright &y& Elsevier]

Abstract: It is shown that superconducting currents in thin-film rings irradiated by coherent microwave field can decay with emission of photons. When the ring thickness is less than the field penetration depth, the field induces coherent oscillations of all the Cooper pairs in the ring. The oscillating condensate will emit photons with energies determined by the difference of quantized energy levels of the superconducting ring. The probability of the microwave field-induced single-photon decay of the supercurrents is calculated. The angular distributions of the photons emitted by the superconducting rings and the lifetimes of the current states, depending on both the ring sizes and the fluxoid numbers in the initial states, are studied. [Copyright &y& Elsevier]

Abstract: The experiment for preparing MgB2 thin films by electron beam (e-beam) annealing of Mg–B multilayer is reported. The annealing process lasts less than 1s, which effectively suppresses the volatility of Mg as well as the reaction of Mg and oxygen. The influence of annealing parameters on the film quality including exposure time, accelerating voltage and beam current is investigated. It is found that e-beam with lower accelerating voltage can acquire MgB2 film with smaller annealing energy density. Also, double e-beam scan annealing process helps to obtain more uniform MgB2 thin films than the single scan. This rapid annealing method synthesizes MgB2 thin films with critical temperature Tc of 35K and critical current density Jc at 15K of 7.6×106 Acm−2. [Copyright &y& Elsevier]

Abstract: The application of flat superconductor rings has been investigated in the structure of inductive shield-type high temperature superconducting fault current limiters, HTc-SFCL. A laboratory scale inductive shield-type HTc-SFCL has been designed and fabricated using flat superconductor rings. The fabrication process has been fully presented. YBCO powder has been used for the fabrication of superconductor rings. This fabrication process, being quite innovative, is introduced completely. The method of the trapped field measurement has been used for the critical current density measurement of the fabricated superconductor rings. The device with nominal current of 2A was tested in a 30V circuit. The SFCL successfully limited the fault currents of up to 10 times the nominal current to an approximately fixed value of 3A. The voltage–current characteristic of the fabricated prototype has also been obtained and has shown compatibility with the fault current limitation results. [Copyright &y& Elsevier]

Abstract: This paper investigates the way in which the levitation gap of an electromagnetic suspension (EMS) system affects the current decay rate of superconducting electromagnet (SC-EM) operated in persistence-current mode (PCM). Using inductance analyzed from the magnetic circuit of an EMS model, the current decay rate caused by the variation in the levitation gap was simulated. In order to experimentally verify the simulation results, we fabricated a small-scale EMS model with SC coil operated in PCM and measured the current decay rates at different levitation gaps. The result showed that the presence of iron core provides a significant benefit in the PCM performance of SC coil, but the benefit decreased as the levitation gap increases. This study revealed that the increased levitation gap of the EMS model with the SC-EM could negatively affect the design of SC-EM operated in PCM. [Copyright &y& Elsevier]

Abstract: Phase dynamics of disordered Josephson junction ladders (JJLs) driven by external currents which are spatially and temporally modulated is studied using a numerical simulation based on a random field XY model. This model is considered theoretically as an effective model of JJLs with structural disorder in a magnetic field. The spatiotemporal modulation of external currents causes peculiar dynamical effects of phases in the system under certain conditions, such as the directed motion of phases and the mode-locking in the absence of dc currents. We clarify the details of effects of the spatiotemporal modulation on the phase dynamics. [Copyright &y& Elsevier]

Abstract: The voltage response of a Josephson junction to a pulsed terahertz current is evaluated in the limit of a negligible junction capacitance (overdamped limit). The time-dependent superconductor phase difference across the junction is calculated in the framework of the standard resistive shunted junction model by using a perturbative method. The pulsed current bias affects the time average value of the voltage across the junction and current steps are induced in the current–voltage characteristics for voltage values depending on the pulse repetition rate. The current step height is proportional to the square of the pulse time width (τ) to the period (T) ratio. A fast response detector for pulsed Terahertz radiation is proposed, with an expected responsivity of the order of 0.1V/W and an equivalent noise power of about 3×10−10 W/Hz1/2. [Copyright &y& Elsevier]

Abstract: The calculation scheme for periodic solutions in an rf-driven Josephson junction including interference current is derived by using the incremental harmonic balance method. The approximate analytical expressions of stable and unstable periodic orbits are obtained. The stability and bifurcation of the periodic solutions are analyzed based on Floquet theory. The results show that, with the increase of the driving amplitude, one of the periodic solutions undergoes symmetry-breaking and period-doubling bifurcation, which leads to chaos eventually. However, the other periodic solution of the system disappears via a saddle-node bifurcation. [Copyright &y& Elsevier]

Abstract: Within the t–t′–J model, the doping dependence of the Meissner effect in cuprate superconductors is studied based on the kinetic energy driven superconducting mechanism. Following the linear response theory, it is shown that the electromagnetic response consists of two parts, the diamagnetic current and the paramagnetic current, which exactly cancels the diamagnetic term in the normal state, and then the Meissner effect is obtained for all the temperature T ⩽ T c throughout the superconducting dome. By considering the two-dimensional geometry of cuprate superconductors within the specular reflection model, the main features of the doping and temperature dependence of the local magnetic field profile, the magnetic field penetration depth, and the superfluid density observed on cuprate superconductors are well reproduced. In particular, it is shown that in analogy to the domelike shape of the doping dependent superconducting transition temperature, the maximal superfluid density occurs around the critical doping δ ≈0.195, and then decreases in both lower doped and higher doped regimes. [ABSTRACT FROM AUTHOR]

Abstract: This work compares the normal-current in a NM/Fi/NM junction with the super-current in a SC/Fi/SC junction, where both are topological insulator systems. NM and Fi are normal region and ferromagnetic region of thickness d with exchange energy m playing a role of the mass of the Dirac electrons and with the gate voltage VG , respectively. SC is superconducting region induced by a s-wave superconductor. We show that, interestingly, the critical super-current passing through a SC/Fi/SC junction behaves quite similar to the normal-current passing through a NM/Fi/NM junction. The normal-current and super-current exhibit N-peak oscillation, found when currents are plotted as a function of the magnetic barrier strength χ ∼ md/ vF . With the barrier strength Z ∼ VGd/ vF , the number of peaks N is determined through the relation Z ∼ Nπ + σπ (with 0< for χ < Z). The normal- and the super-currents also exhibit oscillating with the same height for all of peaks, corresponding to the Dirac fermion tunneling behavior. These anomalous oscillating currents due to the interplay between gate voltage and magnetic field in the barrier were not found in graphene-based NM/Fi/NM and SC/Fi/SC junctions. This is due to the different magnetic effect between the Dirac fermions in topological insulator and graphene. [ABSTRACT FROM AUTHOR]

Abstract: Performance of a resistive superconducting fault current limiter (SFCL) component is usually limited by temperature rise associated with energy input by fault current application during a fault. Therefore, it is expected that short application of the fault current may enhance the power ratings of the component. This can be accomplished by a combination of a HTS component and a mechanical switch. The fast switch (FS) developed recently enables the fault duration to be as short as 1/2 cycle after a fault. Various second-generation (2G) high temperature superconductors (HTS) and YBCO thin films have been tested. The relation between the rated voltage V and the fault duration time t was found to be V 2 ∼ t− 1. Based upon the relation, we predict that when the FS break the fault current within 1/2 cycle after a fault, the amount of HTS components required to build an SFCL can be reduced by as much as about 60%, of that when breaking the fault current at three cycles. [ABSTRACT FROM AUTHOR]

Abstract: Conventional electric power networks were designed and operated not considering fault current limiting devices. Therefore, the performance and characteristics of resistive superconducting fault current limiter (SFCL) should be reviewed considering the coordination with other electric circuit protecting devices. In this paper, real field application issues of resistive SFCL were investigated considering utilities’ demands and coordination with other protection devices. Pure resistive SFCL and hybrid resistive SFCL were compared in order to determine suitable solutions for electric power systems. SFCLs were modeled and analyzed using electro-magnetic transients program (EMTP) and their performances were compared to identify the adaptability to the conventional power networks. Consequently, Simulation results showed that hybrid resistive SFCL have more advantages than pure resistive SFCL considering the requirements and specification for the distribution networks. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we analyzed recovery characteristics of matrix-type SFCLs (MFCL) with 2×3 matrixes when triple lines-to-ground fault occurred. MFCLs used in this work consist of 18 superconductors, six reactors for induction of magnetic field and several parallel impedances for bypassing fault currents. Also we analyzed recovery characteristics of resistive-type SFCLs of which 18 superconductors are connected in series and parallel, without reactors and parallel impedances, for the purpose of comparison, under the same experimental conditions of MFCLs. Experimental results were reported in terms of recovery characteristics for individual superconductors in an R phase, dependency of faults cycles and applied fault voltages in each phase. We confirmed that recovery characteristics of MFCLs were more excellent than those of resistive-type SFCLs. [ABSTRACT FROM AUTHOR]

Abstract: On the basis of a voltage compensation type active superconducting fault current limiter (SFCL) proposed in previous work, the effects of this type SFCL on distance relay protection are studied in this paper. Under the condition that the active SFCL is placed behind the relay element, its current-limiting impedance will be added into the measured impedance between the relay and the fault points. As a result, in order to prevent the refused operation of the relay, the measured impedance should be revised. According to the three different operation modes of the active SFCL, we present the corresponding three modified formulas. Furthermore, using MATLAB, the model of the dual-source power system with the active SFCL is built, and the impacts of the active SFCL on the distance relay protection are studied in detail under the different current-limiting modes and fault distances. The simulation results show that: without using the modified formulas, the introduction of the active SFCL will reduce the protection distance of the relay, and in the case that the modified formulas are adopted, the three modes of the active SFCL will not affect the measured impedance of the relay, and further the validities of the proposed modified formulas can be testified. [ABSTRACT FROM AUTHOR]

Abstract: When the fault occurred in the power system, the superconducting fault current limiter (SFCL) rapidly limited the fault current to protect the power devices with preventing power failure. Therefore, the application of the matrix-type SFCL in the power system could improve of its reliability and stability. To apply the SFCL into the real power system, many superconducting elements should be connected in series and parallel. If any superconducting element of the matrix-type SFCL breaks down, it cannot basically limit the fault current. In this paper, we analyzed operation stability of the matrix-type SFCL which was divided into trigger and current-limiting parts as follows: Case 1. Break-down of a superconducting element in the trigger part. Case 2. Break-down of a superconducting element in the current-limiting part. Case 3. Break-down of two superconducting elements in the current-limiting part. When any superconducting element was broken down, we confirmed that all fault current flowed into other normal superconducting element connected in parallel and its power burden was largely increased. At that time, the matrix-type SFCL was operated well to limit the fault, but the fault current was decreased a little bit because the resistance generated in the superconducting element was abruptly increased. If the excessive current of the superconducting element exceeds its capacity, it could cause the break-down of the other superconducting element, shunt resistors, or shunt reactors, and then the break-down could be extended to the whole matrix-type SFCL. Through these results, we found that the number of superconducting elements connected in series and parallel should be designed with enough margins against the break-down of superconducting elements and optimal conditions for shunt resistors and reactors should be determined. [ABSTRACT FROM AUTHOR]

Abstract: Compared with the first-generation BSCCO wire, the YBCO thin-film wire boasts low material costs and high J c and superior magnetic-field properties, among other strengths. Meanwhile, the previous BSCCO wire material for superconducting cables has been researched on considerably with regard to its post-wire quenching characteristics during the application of an alternating over-current. In this regard, the promising YBCO thin-film wire has yet to be further researched on. Moreover, still lacking is research on the YBCO thin-film wire with insulating layers, which is essential in the manufacture of superconducting cables, along with the testing of the application of an alternating over-current to the wire. In this study, YBCO thin-film wires with copper-stabilizing layers were used in testing alternating over-current application according to the presence or absence of insulating layers and to the thickness of such layers, to examine the post-quenching wire resistance increase and quenching trends. The YBCO thin-film wire with copper-stabilizing layers has a critical temperature of 90K and a critical current of 85Arms. Moreover, its current application cycle is 5.5 cycles, and its applied currents are 354, 517, 712, and 915Apeak. These figures enabled the YBCO thin-film wires with copper-stabilizing layers to reach 90, 180, 250, and 300K, respectively, in this study. These temperatures serve as a relative reference to examine the post-quenching wire properties following the application of an alternating over-current. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the superconducting fault current limiter (SFCL) with two trigger current levels was suggested and its effectiveness through the analysis on the current limiting characteristics was described. The proposed SFCL, which consists of the triggering and the limiting components, can limit the fault current by generating the limiting impedance through two steps according to the amplitude of the initial fault current. In case that the fault happens, the lower initial fault current causes the only superconducting element of the triggering component to be quenched. On the other hand, the higher initial fault current makes both the superconducting elements comprising the triggering and the limiting components of the SFCL to be quenched, which contributes to the higher impedance of the SFCL. Therefore, the effective fault current limiting operation of the SFCL can be performed by generating the SFCL’s impedance in proportion to the amplitude of the initial fault current. To confirm the current limiting operation of the proposed SFCL, the short-circuit tests of the SFCL according to the fault angle were carried out and its effective fault current limiting operations could be discussed. [ABSTRACT FROM AUTHOR]

Abstract: In Japan, the development of a 275kV class YBCO power cable was started in 2008 with the support of the New Energy and Industrial Technology Development Organization (NEDO). In the designing of 275kV YBCO power cable, the thickness of insulator is required to be 26mm. Thus, in order to design the 275kV YBCO power cable, it is important to estimate the thermal diffusion through the electrical insulation layer for designing the high-voltage YBCO power cable. Furthermore, YBCO power cables might be subjected to short-circuit fault currents that are 10–30 times a normal operating current. Therefore, in order to ensure stability and feasibility of superconducting power cables, we need to investigate the thermal characteristics and current distribution in the cable in the normal and fault conditions. The objective of this study is to investigate the thermal characteristics and dielectric performance in 275kV class power cables. We carried out experiments on dummy cables in a steady state to clarify the distribution of temperature. In order to estimate the thermal conductivity and the heat capacity of the insulation layer, we performed numerical simulations using a developed computer program on the basis of the 3D finite element method. We also measured a tanδ and permittivity of an insulation layer in order to investigate the dielectrical performance. [ABSTRACT FROM AUTHOR]

Abstract: Since a 100m, 22.9kV/50MVA high temperature superconductor (HTS) cable system was installed at the Gochang test yard of Korea Electric Power Corp. (KEPCO) in 2005, a long-term test has been performed. In this paper, the transport characteristics of the KEPCO HTS cable system were examined by the electrical and calorimetric methods. To analyze the shield current in this system, an equivalent circuit model for the KEPCO HTS cable was suggested, and the calculated shield current compared with the measured one. The results show that the electrically measured total loss, which includes the AC and ohmic losses, corresponds well with the loss measured from the calorimetric method. The measured AC loss of the HTS cable is proportional to the 2.5th power of transport current, and four times larger than the conductor loss calculated from the monoblock model. This is because the conductor’s geometry in the HTS cable is not identical to a cylindrical superconductor in the monoblock model, its temperature rises due to a thick insulator, and the shield loss is included in the measured AC loss. In addition, the measured AC resistance of the current-lead is constant regardless of transport current, particularly in the low current region. Finally, the shield current calculated from our equivalent circuit model is in good agreement with the measured one. [ABSTRACT FROM AUTHOR]

Abstract: The new Japanese national project of development of 66kV/5kA high-temperature superconducting (HTS) power cables has been started since 2008. In an AC power system, a fault current may flow in the event of a short circuit accident. The maximum fault current condition is defined to be 31.5kArms for duration of 2s for 66kV class transmission line in this project. Therefore, one of the technical targets in this project is to design the HTS power cable to survive at this fault current condition. The coated conductors have copper layer as a stabilizer not to be damaged by over-currents. The HTS cable has a copper former and copper shield layers in parallel with the HTS conductor layers and HTS shield layers, respectively, to control the temperature rises in the HTS cable at a fault accident. In this study, we simulated the maximum temperature rises in the HTS power cable at the fault current condition of 31.5kArms for 2s in order to design the copper stabilizer and copper shield layers by using a computer program we developed on the basis of 3D finite element method (FEM) and electrical circuit model. [ABSTRACT FROM AUTHOR]