Self-field and geometry effects in transport current applications of multifilamentary Bi-2223/Ag conductors

This paper describes quantitatively the influence of the self-field and the cross-sectional geometry on the effective critical current and the ac losses in transport current applications of nontwisted multifilamentary Bi-2223/Ag conductors. The results are obtained with finite-element method simulations. The numerical implementation includes an anisotropic model for the dependence of the critical current density J/sub c/ and the power index n on the local parallel and perpendicular magnetic field components. The relation is given between the intrinsic critical current density and the effective critical current for different multifilamentary conductors. Shown are examples of the current and magnetic flux density distributions in order to demonstrate their effect on the ac losses in self-field.     

Analysis of DC Power Transmission Using High T_c Superconducting Cables

A conceptual superconducting DC cable model is designed and its magnetic fields distribution is analyzed with Ansoft/Maxwell soft. A DC Power transmission system is also studied by using the Matlab/Simulink. With the DC Line and AC Ground Fault, the system losses analysis is introduced.The analysis results mainly include the magnetic fields distribution of the HTS cable model with Ansoft/Maxwell, the system loss, the DC Line and AC Ground Fault with Matlab/Simulation.     

Analysis of DC Power Transmission Using High Tc Superconducting Cables

A conceptual superconducting DC cable model is designed and its magnetic fields distribution is analyzed with Ansoft/Maxwell soft. A DC Power transmission system is also studied by using the Matlab/Simulink. With the DC Line and AC Ground Fault, the system losses analysis is introduced.The analysis results mainly include the magnetic fields distribution of the HTS cable model with Ansoft/Maxwell, the system loss, the DC Line and AC Ground Fault with Matlab/Simulation.     

Geometry considerations for use of Bi-2223/Ag tapes and wires withdifferent models of Jc(B)

In typical power applications, Bi-2223 conductors carrying AC current will be subjected to external magnetic fields whose orientation and conductor's geometry are of major significance for the AC loss magnitude. This paper investigates the influence of the geometry and aspect ratio of nontwisted Bi-2223 conductors in reducing the AC loss for such applications. A numerical model of high-T_c materials has been used in finite-element-method (FEM) simulations. The model incorporates power-law E-J characteristics with J_c and n defined by both parallel and perpendicular local magnetic field components. It allows computations of field and current distributions with transport current and/or applied field of any orientation. Monofilamentary tapes of rectangular and elliptical geometry with anisotropic J_c(B), as well as square and round wires with isotropic J_c(B) have been used for simulations under various operating conditions. A comparison between AC losses, magnetic field, and current distributions in the tapes and wires is presented     

Output interface with latching driver for LTS-SFQ circuits

We propose an output interface with a latching driver for single-flux-quantum (SFQ) circuits operating at 4.2 K. An optimum critical current density J/sub c/ of the latching driver was discussed, and a multichip module (MCM) structure with SFQ circuits and latching drivers was proposed for 40-Gb/s operation. To optimize J/sub c/ of the latching driver, we calculated the punchthrough probability of Nb-Al-AlO/sub x/-Nb junctions and high-temperature superconductor (HTS) junctions. The Nb junction with a J/sub c/ of 45 kA/cm/sup 2/, which has a hysteresis of 44% for the latching operation, leads to a punchthrough probability lower than 10/sup -15/ for an ideal ac-bias of 40 GHz. On the other hand, ramp-edge-type interface-modified junctions based on YBa/sub 2/Cu/sub 3/O/sub 7-x/ have an optimum J/sub c/ of 60 kA/cm/sup 2/ that gives the smallest punchthrough probability lower than 10/sup -15/ for an ideal ac-bias of 40 GHz without any shunt capacitance. Because the optimum J/sub c/ of 45 kA/cm/sup 2/ for the latching driver is too large to fabricate large-scale integrated SFQ circuits with the Nb junction, the MCM structure consisting of SFQ circuits and latching drivers with the optimum J/sub c/ is important to prepare 40-Gb/s SFQ systems. The J/sub c/ of 60 kA/cm/sup 2/ is a practical value for the HTS junctions, and use of the low-temperature superconductor (LTS)-HTS MCM structure is also one way to realize the high-speed SFQ systems.     

Characteristics Measurements of HTS Tape with Parallel HTS Tapes

Many high temperature superconducting (HTS) tape manufactures make an effort to reduce the transport current loss of HTS tapes. The knowledge of critical current and self-field in an HTS tape is very useful to compute the transport current losses. The spatial distribution and magnitude of self-field are variable due to the neighboring materials. In this paper, the critical currents and the transport current losses of BSCCO and YBCO tapes with paralleled magnetic material (Ni tape) and/or diamagnetic material (BSCCO tape) are experimentally investigated to improve the AC loss properties. The critical currents of HTS tapes with paralleled Ni tape are slightly decreased and the transport current losses are markedly increased. However, the critical currents and transport current losses of HTS tapes with paralleled BSCCO tape have not current carrying are more improved than single HTS tape.     

AC Loss Characteristics of YBCO Coated Conductors With Varying Magnitude of Critical Current

Three YBCO coated conductors with various critical currents, up to 189 A, were prepared. The magnetization losses without transport current and the total AC losses of the conductors carrying various transport currents in transverse magnetic fields with various orientations were measured electromagnetically to study the AC loss characteristics systematically. The measured total AC losses were compared with the numerical values using a one-dimensional FEM model.     

AC Transport Current Loss Characteristics of REBCO Coated Conductors Subjected to Bending Strains

We experimentally investigated dependence of AC transport current loss characteristics of HoBCO on bending strains. The losses were compared with the losses in the straight conductors. The measurement results showed that values of the AC losses were affected by the bending strains. However, when the losses and the amplitudes of the transport currents were normalized by the strain dependent critical current, curves of the losses vs. the amplitude of the currents fell into one curve unless superconducting layers of the conductors get damages caused by bending strains. Based on these results, it can be considered that the AC transport current loss characteristics of HoBCO subjected to bending strain can be estimated by knowing values of critical currents of bent conductors and the loss characteristics of straight ones in the range where the bending strains do not damage the superconductor layers.     

Loss and dynamic magnetic field measurements in LHC dipoles

Knowledge of AC loss and dynamic magnetic field distortion in the main LHC dipoles is both important for the assessment of the accelerator performance and providing insight into the properties of assembled magnets. We measured the loss due to the current cycling in a few 1-meter long model dipoles, 15-meter long dipole prototypes and pre-series magnets. As expected the loss depends linearly on the rate of the current change. From the slope of this dependence, the contact resistance between the strands of the opposite layers of the cable, R/sub c/, was evaluated for the inner winding of the dipole. We discuss the method to estimate the R/sub c/ value in the outer winding. The R/sub c/ value has been also derived independently from measurements of the magnetic field. For this, the ramp rate dependent component of the main field as well as of the harmonics has been measured. The main magnetic field measurements were performed using both stationary coils and Hall probes. Rotating coils were used to perform the harmonic measurements.     

Losses in a BSCCO/Ag tape carrying AC transport currents in ACmagnetic fields applied in different orientations

In most prospective electric power applications of high-temperature superconductors (HTSs), the conductor is wound in a coil configuration. For a coil of finite length, the magnetic field orientation is axial in the middle of the coil, while the field contains a substantial radial component at the coil ends. In a superconducting BSCCO/Ag tape, the AC losses depend strongly on the orientation of the magnetic field. In this study, we present experimental results of the AC losses in a multifilamentary silver-sheathed Bi-2223 HTSs tape, carrying alternating transport currents in externally applied alternating magnetic fields at different orientations, with respect to the face of the tape and perpendicular to the transport current. The AC losses were measured calorimetrically, at fixed temperature and frequency. The results are compared to semi-empirical models of the AC losses in HTSs tape. We present a more general model of the angular dependence of the AC losses     

Thermal and electrical stabilization of high-temperature superconductor powder-in-tube conductor

High-temperature superconductor (HTS) powder-in-tube conductors often require thermal and/or electrical stabilization to ensure their long-term integrity. An example of such a stabilization need is the safety bypass lead of an HTS current lead intended for application to superconducting magnetic energy, storage (SMES) devices. The bypass lead functions include current sharing during upset conditions and conductor element temperature control. This paper presents a bypass lead design for an HTS current lead in an 0.5 MW h SMES system. Included are predictions of thermal and electrical stabilization and current lead heat leaks. The results of a supporting development program are presented, as are details of a method to connect conductor element/bypass leads, an assembly procedure, a cleaning method, and thermal-stress tolerance measurements.     

Impact of DC components in transport current and external magnetic field on hysteresis losses in an HTS tape

The high-temperature superconductor (HTS) development is presently intensive, and one can expect that HTSs will be used in different electric devices in the future. In some of these devices, e.g., a magnetostrictive actuator, the conductor will be exposed to both ac and dc transport currents and external magnetic fields. One of the most important parameters in the design of electric devices is the power loss. It is, therefore, of importance to develop models that are able to predict the power loss in devices based on HTSs. In this paper, we present an experimental characterization of the hysteresis losses in an HTS tape exposed to ac or dc transport currents in combination with external magnetic fields. The experimental results are compared to some existing models based on the critical state model. The power loss was measured on a multifilamentary Bi-2223 tape at constant temperature (70 K) and frequency (50 Hz).     

Flux trapping in a ring-shaped YBCO bulk by pulsed fieldmagnetization

A pulsed magnetic field can be applied using small coils to generate a strong magnetic field for the magnetization of the high-Tc superconductors (HTS) to be used as quasi-permanent magnets in flywheels and motors. The dynamic electromagnetic behavior of two melt-processed ring-shaped Y-Ba-Cu-O bulks using the pulsed field magnetization (PFM) process has been experimentally investigated and analyzed. The flux trapped in the bulk by PFM process was compared to the flux trapped by field cooling process. Both cases then have been analyzed with a numerical model based on the finite-element method (FEM). The power-law model was utilized to relate the electric field to the current density inside the superconductor. The dependence of the critical current density on the magnetic field density was taken into account. Measured and calculated results are compared and discussed     

Electromagnetic Field Analysis of YBCO Coated Conductors in Multi-Layer HTS Cables

Electromagnetic field analyses of YBCO coated conductors in mono-layer and multi-layer high$ T_ c$superconducting (HTS) cables with practical configurations were carried out to calculate their AC losses. Numerical models employing one-dimensional FEM and two-dimensional FEM were used in the analyses. The error of the 1D-model was assessed by comparing the loss calculated by the 1D-model and that calculated by the 2D-model. The gap between the conductors in each layer, the relative position of conductors in the inner layer and in the outer layer, and the number of layers were varied to study their influence on the AC loss. The numerically calculated AC losses were compared with the analytical values.     

高温超导直线感应电机的设计和电磁分析

本文介绍了高温超导直线感应电机的设计和电磁分析方法。首先,使用遗传算法得到一组优化的电机参数;然后,为了确定电机参数的准确性需要用有限元方法对得到的电机参数建模仿真;垂直穿过高温超导绕组的磁场(垂直磁场)对电机的临界电流影响很大,为了增加电机的临界电流,穿过电机初级超导绕组的垂直磁场应该尽可能地小。最后,要对建立的电机模型进行详细的电磁分析,以保证各项性能指标满足要求。     

Method for estimating future markets for high-temperature superconducting power devices

This paper describes a spreadsheet model for estimating the impact of high-temperature superconducting (HTS) power devices on the national electric grid. The distribution of losses in the national grid is carefully traced and those losses that HTS can eliminate are identified. The energy savings achievable by the many sizes of HTS generators, transformers, cables, and motors are then computed and totaled using a spreadsheet analysis. The economic savings are very sensitive to the price (and J/sub e/) of HTS wire, and to the cost of cooling the devices to operating temperature. A market penetration model is used to estimate how fast HTS devices become commercially,successful. The emphasis of the paper is the analytic tool, not the numerical results of one specific case. This entire model is explicitly designed to allow others to enter their own estimated parameters and arrive at their own conclusions.     

Transport AC Losses in YBCO Coated Conductors

Modeling and design of superconducting power devices (e.g. fault current limiters), based on second generation HTS tapes, requires accurate evaluation and prediction of AC losses. Transport AC losses measurements have been performed on samples of YBCO coated conductors at 77 K, as a function of current. The results have been compared with the classical analytical model for self field AC losses calculation, taking into account the role of the magnetic substrate.     

The influence of oxygen partial pressure on growth of the (Hg,Re)-1223 intergrain junction

Hg/sub 0.82/Re/sub 0.18/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub 8+/spl delta// polycrystalline samples were successfully obtained by using different oxygen partial pressure in the annealing treatment of the precursor ceramic. The doping state was confirmed by X-ray powder diffraction pattern analysis and by observing distinct thermopower values at room temperature. Also, the intergrain regions have shown an improvement in the critical current density when using the precursor preparation with 10% O/sub 2/ and 90% Ar (optimal doped). The optimal doped sample has presented the highest /spl alpha/ exponent of the J/sub c//spl prop/[1-(T/T/sub c/)/sup 2/]/sup /spl alpha// dependence. For the case of (Hg,Re)-1223 polycrystalline superconductor applications, the /spl alpha/ exponent can be used as a junction quality parameter.     

Design of superconducting MRI surface coil by using method of moment

A method of moment with an enhanced model to design high-temperature superconductor (HTS) RF surface coils for magnetic resonant image (MRI) is presented. The resonant frequency and quality factor (Q) of HTS RF spiral coils are simulated using this method. The agreements of resonant frequencies and Qs between the simulation and measurement are excellent with differences less than 1 % and 3 %, respectively. The 0.2-/spl mu/ m-thick YBaCuO (YBCO) thin films are deposited onto single side of 0.508-mm-thick LaAlO/sub 3/ (LAO) and sapphire substrate and patterned into a spiral shape. To accurately analyze the resonant frequency and Q of a coil, an enhanced two-fluid model is employed. HTS RF coils with diameter of 65 mm for 0.2 T and 1.5 T MRI systems are designed and fabricated with the measured Q of 19 K and 23 K, respectively. In addition, the shift of resonant frequency due to the mutual coupling between two HTS spiral coils is predicted by this method, which is important for design of HTS coil arrays in an MRI system.     

Macroscopic numerical evaluation of heat generation in a bulk highTc superconductor during pulsed field magnetization

Pulsed-field magnetization of a bulk high Tc superconductor (HTS) is evaluated by using a macroscopic numerical simulation code. Local heat generation in the HTS during the pulsed-field magnetization is discussed to clarify the dynamic magnetization process. Nonlinear dependence of shielding current on the dynamic magnetic field is considered by using the flux flow-creep model. Dependence of flow resistivity on the magnetic field and temperature are also evaluated with the Bardeen-Stephen and the Tinkham models. It is numerically confirmed that reported experimental results are due to a decrease of the shielding current caused by local heat generation