Conductivity Performance Research Articles

A Cryogen-Free 25-T REBCO Magnet with the Extreme-No-Insulation Winding Technique.

We present the operation result of a cryogen-free 23.5 T/φ12.5 mm-cold-bore magnet prototype composed of a stack of 12 no-insulation (NI) REBCO single pancake coils-ten middle coils of 6-mm wide and two end coils of 8-mm wide tape-forming 6 double pancake (DP) coils with inner joints. Each coil was wound with the tape having only 1-μm-thick copper layer on each side to overcome the conductor thickness uniformity issue and enhance the mechanical strength within the winding, and then, additional electrical shunting by thin layers of solder was applied on the top and bottom surfaces of each DP coil for effective cooling and quench protection-called extreme-NI winding technique. With this small prototype magnet towards a benchtop 1-GHz NMR, we validate our coil design that include conductor performance, screening-current-induced field and stresses, and conduction-cooling cryogenics. Included in the paper are: 1) conductor issues and our counterproposal in winding; 2) screening-current reduction method; 3) design and manufacture summary of the magnet; and 4) operating test results of the magnet up to 25 Tesla.

Experimental Study on the Influence of Cross-Section Type of Marine Cable Conductors on the Bending Performance

Through the development of marine energy, marine cables are the key equipment for transmission of electrical energy between surface platforms and underwater facilities. Fatigue failure is a critical failure mode of marine cables. The bending performance of the cable conductor has a major influence on both bending and fatigue performances of the overall cable structure. To study the influence of different types of the conductor cross-section on the bending performances of marine cable conductors, three types of copper conductors with the same cross-sectional area, i.e., noncompressed round, compressed round, and shaped wire conductors, were selected. The experimental results demonstrated that the cross-section type significantly affects the bending performances of copper conductors. In particular, the bending stiffness of the shaped wire conductor is the highest among the three conductor types. Four key evaluation parameters, i.e., the bending stiffness, maximum bending moment, envelope area, and engineering critical slip point, were selected to compare and analyze the bending hysteresis curves of the three copper conductors. The differences in the key evaluation parameters were analyzed based on the structural dimensional parameters, processing methods, and classical bending stiffness theoretical models of the three copper conductor types. The results provide an important theoretical guidance for the structural design and engineering applications of marine cable conductors.

Characteristic Mode Formulations of Composite PEC and Lossy Dielectric Objects

Lossy dielectric substrate affects the performance of a nearby perfect electric conductor (PEC) antenna. This letter presents a set of formulae for characteristic mode analysis (CMA) of composite PEC and lossy dielectric objects. It is based on the volume-surface integral equation and substructure treatment that separates the radiation and dissipation powers of the composite structure. A narrow PEC plate (that represents a dipole antenna) is placed in proximity of a thick, lossy dielectric material, and CMA of this structure is presented as an example. The separation gap between the PEC and dielectric objects affects the resonance and radiation efficiency of the antenna, and it is shown that CMA accurately captures those effects. The influence of dielectric loss on the modal orthogonality is discussed. Since the PEC item dominates over the coupling one in the substructure operator, the computed modes maintain good orthogonality with low-loss dielectrics. Owing to the physical insights of CMA, it has many potential applications associated with lossy materials.

Improved mechanical models and Ic estimation for the whole life cycle of high temperature superconducting coated conductors

To evaluate the effect of mechanical behaviors on the critical current (Ic) of superconducting conductors, this paper develops an improved modeling method at all the composite-layer, conductor, and cable levels, which provides a means to analyze the stress and strain for the whole manufacture process. First, a sandwich model based on composite shells was developed to calculate the residual thermal stress of coated conductors during the fabrication process. Then, the uniaxial tensile model was used to verify the loading method for applying the residual thermal stress to subsequent models as initial conditions. With the pre-stress loaded, mechanical behaviors of coated conductors under bending and torsion were analyzed. Further, an exponential function model was adopted to describe the relationship between the normalized critical current and longitudinal strain. Lastly, a series of numerical models were built to analyze the bending behavior of CORC (conductor on round core) cables. Combined with tests of a sample cable, the strain-dependent critical current predicted the Ic degradation under different bending radii. Calculation results show that the sandwich model is hundreds of times faster than other applicable finite element (FE) models. The loading method provides the initial stress for any geometry and software to precisely analyze the stress of coated conductors, especially the rare earth-barium-copper-oxide (ReBCO) layer with intrinsic compressive stress. The electromechanical behaviors of bending and torsion are in good agreement with experimental data, and the exponential mode obtained from conductor performance can estimate Ic degradation of the CORC cable within a relative error of 1.46 % in the reversible region.

Conductor design and performance analysis for CFETR magnet

The design work of the China Fusion Engineering Test Reactor (CFETR) was carried out in the past years. The magnet system is composed of 16 toroidal field (TF) coils, 8 central solenoid (CS) coils, and 7 poloidal field (PF) coils. The maximum magnetic field on the TF coils is 14.4 T. Three grades of cable-in-conduit conductors (CICCs), including high-Jc Nb3Sn strand, ITER-like Nb3Sn strand, and NbTi strand, have been chosen for the TF WP winding in high, medium, and low magnetic fields. High-Jc Nb3Sn strand will also be applied in the CS conductor considering the maximum magnetic field, which is higher than the TF coil. For the PF coil, the ITER-like Nb3Sn strand will be applied in Conductor PF1 and Conductor PF7, and NbTi will be applied in others. In this paper, conductor designs for the CFETR magnet including design criteria, choice of conductor configurations, and conductor performance analysis are presented.

Insights on the electrochemical performance of a molten proton conductor fuel cell with internal methanol reformer

A fuel cell based on a molten proton conductor electrolyte membrane, in which polybenzimidazole (PBI) membrane is doped with molten CsH5(PO4)2, has been integrated in a single cell arrangement with a CuZn-based methanol reformer. It is demonstrated that the fuel cell with the internal reformer can efficiently operate at 220 °C, which is higher temperature than the upper limit of previously reported high-temperature proton exchange membrane fuel cell with an H3PO4-doped PBI membrane. Furthermore, the fuel cell with the internal reformer is able to provide 0.7 V at 200 mA cm−2 at 220 °C, keeping an open circuit voltage above 1 V, similarly with that under hydrogen feed at the same temperature. Electrochemical characterization of anode electrode surface area, also employing cyclic voltametry and impedance spectroscopy suggests that a performance decay after a transient operation with several on-off cycles, is due to proton conductor loss in the electrode's catalyst layer of the single cell.

Location and corrosion detection of tower grounding conductors based on electromagnetic measurement

Tower grounding conductors are buried underground and serve as the grounded discharge channel for the fault or lightning current of a transmission power system. The performance of the grounding conductor is crucial for the safe and reliable operation of transmission power systems. This study proposes a steel corrosion detection and location method for tower grounding conductors using electromagnetic measurements. To measure the surface alternating current magnetic field from the tower grounding conductor, a three-axis magnetic sensor array was constructed using six anisotropic magnetoresistive (AMR) magnetic sensors with a small size (mm3). Through simulation analysis, the structural size of the magnetic sensor array was determined, and the feasibility of the detection principle was analyzed. The experimental results showed that the detection accuracy of the grounding conductor position can reach ± 0.1 m. The maximum deviation of the depth detection was 0.0964 m for the square-type grounding conductor. Furthermore, the simulation and experiment demonstrate that the value of fuzzy closeness decreases gradually with an increase in the degree of corrosion of the grounding conductor, proving that the degree of corrosion of the grounding conductor can be evaluated according to the value of fuzzy closeness. The proposed method has significant potential for engineering applications in the detection and maintenance of tower grounding conductors.

A Reel-to-Reel Scanning Hall Probe Microscope for Characterizing Long REBCO Conductor in Magnetic Fields Up to 5 Tesla

We have developed and routinely used a reel-to-reel (R2R) scanning Hall-probe microscopy (SHPM) system to characterize REBCO conductors developed at the University of Houston. By mapping the screening-current-induced field of a magnetized REBCO conductor, the SHPM system enables 2-dimensional imaging of critical current density (<i>J</i>_c) distribution in a contact-free, non-destructive approach. Most existing SHPM systems investigate the magnetized REBCO conductors at remnant state without external background field. However, because of the inhomogeneity in the distribution of nanoscale artificial pinning centers in advanced REBCO conductors, there is a demand for reel-to-reel in-field examination over long conductor lengths. We have been developing a new R2R SHPM, capable of measuring the <i>J</i>_c profile of long REBCO conductors at the temperature of 63.5&#x2013;77 K and in an applied field up to 5 T. With optimal data acquisition and processing techniques, we overcame the challenge of measuring weak screening-current-field signals in a strong background field. R2R <i>J</i>_c mapping has been performed on long REBCO conductors with a spatial resolution as low as 0.15 mm² and a longitudinal scanning speed comparable with our existing system. Our previous study revealed a good correlation between the REBCO conductors&#x2019; 65-K in-field <i>J</i>_c and their <i>J</i>_c over a wide span of temperatures and fields. Using this correlation, the in-field R2R SHPM will serve not only as a means of quality control, but also provide insight into high-field performance of advanced REBCO conductors at low temperatures.

Evaluating Aeolian Vibration Performance of High-Temperature Low-Sag OHL Conductors

High-Temperature Low-Sag (HTLS) conductor technologies are often implemented, among many approaches, for optimizing the overhead lines utilization. The advancements of HTLS conductors are based on the differences in core and aluminum properties and installation procedures. This non-linear conductor behavior, although considered in the sag-tension calculations, by implementing the knee-point temperature, is often omitted from the aeolian vibration calculations. To understand the implications of the complex HTLS conductor structure on vibrations, a new calculation approach is proposed in this paper to quantify the effect of installation and operating conditions on the performance of any HTLS conductor. The proposed method conceives a prediction lay area that estimates where the actual field data are expected to lay, and is validated with good accuracy against the field data from ACSR, ACCC, and GZTACSR. The developed model enables the prediction of non-homogeneous (composite) conductors and should be implemented at above knee-point operating temperatures with zero aluminum tensions

Experimental Assessment of the Thermal Strain Distribution in Nb3Sn React &amp; Wind Conductor Prototype for European DEMO

In a typical Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn cable for fusion applications, the knowledge of the strain state of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn filaments is important to predict and interpret the conductor performance in operation. Amongst the relevant strain sources, the predominant is the thermal strain that arises during the cool-down of the conductor to operating temperature, due to the different expansion of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and copper in the cable and the stainless steel conduit. This work addresses the characterization of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn thermal strain in the React & Wind prototype (RW2) developed by EPFL-SPC for the toroidal field coil and the central solenoid of the EUROfusion DEMO fusion reactor. AC susceptibility measurements were performed on the RW2 prototype to assess the thermal strain distribution in the cable cross-section, before and after undergoing electromagnetic and thermal cyclic loading. The results of the analysis have shown that RW2 exhibits a significantly lower absolute mean strain value (about −0.3%), compared to many Wind & React ITER conductor samples investigated with the same method. In addition, the analysis highlighted that the assessed thermal strain distribution does not vary significantly before and after the electromagnetic and thermal cycles, confirming the small performance degradation in the RW2 conductor that has been recently reported.

Numerical study on the effect of fin length variation on the thermal performance of a bus duct conductor

This article presents a finite volume-based simulation study on the effect of fin length variation on the thermal performance of a bus duct conductor. The study was conducted by developing a numerical model using ANSYS FLUENT. IEC 60439-1 and IEC 60439-2 standards were employed as a guideline to conduct the experimental setup. It was found that increasing the fin length increases the total heat transfer rate. This is due to an increase in the surface area exposed to the fluid and a decrease in the thermal boundary layer thickness. However, it was observed that longer fin lengths contributed to greater frictional forces on the fluid that resulted in a drop in convective heat transfer coefficient. The current numerical study is expected to provide a better understanding of the effect of fin length on the thermal performance of a bus duct conductor.

인가전압의 크기에 따른 2세대 고온 초전도선재의 열화특성에 관한 연구

2G High temperature superconducting (HTS) GdBCO conductors are usually considered as proper superconductors to develop a superconducting fault current limiter and a superconducting cable which are operated in a high voltage condition. 2G HTS GdBCO conductors manufactured by SuNAM Co., Ltd. can be classified by a metal stabilizer: silver, copper, brass, and stainless steel. In previous study, the electrical performance of 2G HTS GdBCO conductors with copper stabilizer according to electrical breakdown voltage is reported. In this study, dielectric experiments are performed in saturated liquid nitrogen (LN₂) at 77K temperature to analyze the characteristics of electrical degradation such as critical current and index number of 2G HTS GdBCO conductors with copper and brass stabilizer according to amplitude of applied voltage. All dielectric experiments are performed with AC and lightning impulse voltages by using a sphere-to-plane electrode system. It is found that the electrical performance of 2G HTS GdBCO conductors is degraded according to the amplitude of applied voltage.

DC performance and AC loss of sub-size MgB2 CICC conductor for fusion magnet application

Given the low price and relatively high transition temperature (39 K) of MgB2 conductor, MgB2-based superconductors are a potential candidate for the lower field fusion coils, such as poloidal field (PF) coils, correction coils and feeders. However, to date, the application of MgB2 is limited to demonstrators in a low magnetic field of up to 5 T and at temperatures of up to 10 to 20 K, relying on cryogen-free, helium gas or liquid hydrogen cooling, which significantly reduce the cost of cryogenic systems. To demonstrate the feasibility and performance verification of large size MgB2 PF conductors based on ITER and CFETR requirements, a 4th-stage subsize MgB2 cable-in-conduit conductor (CICC) cable sample is made at the Institute of Plasma Physics, Chinese Academy of Sciences. The CICC contains 96 in situ MgB2 superconducting wires, manufactured by Western Superconducting Technology Ltd. and 48 copper wires. The critical current of the sub-size cables and MgB2 witness wires are examined with different background magnetic fields at 4.2 K. In addition, the AC loss is measured utilizing magnetization and calorimetric methods. To further clarify the influence of electromagnetic force on the AC loss performance, the cable sample is pressed transversely at room temperature and then inserted into a dipole magnet for AC loss measurement at 4.2 K. The critical current at 4.2 K of the subsize MgB2 CICC cable shows 20% degradation compared to the witness wires at 2 T background magnetic field. However, no further critical current degradation is visible during ramping up and down the magnetic field. The coupling loss time constant for 1 T background magnetic field amounts to 480 ms. No significant effect of the applied transverse stress on the coupling loss is observed between 0 and 10 MPa.

Wind-induced tension and deflection of multi-span bundled transmission conductors using aeroelastic model wind tunnel test

An aeroelastic model of the two-span six-bundled conductors is fabricated without distortion of conductors, to investigate the performance of wind-excited multi-span transmission conductors. The wind tunnel test is conducted in a wind tunnel with a big size of cross-section to contain the large aeroelastic model of multi-span transmission conductors and measure wind-induced tension and deflection of the insulator. The effects of wind direction, wind speed, and length of insulator on the wind-induced tension and swing angle of the insulator are then investigated based on the wind tunnel measurement. Results show that the mean transverse tension increases with wind direction θ and follows the law of sin2θ when θ > 40°, but is not proportional to the square of mean wind speed VH when VH < 35 m/s. The force coefficient of the tension decreases with increasing θ and wind speed, and is close to 1.0 when θ = 90° and VH > 35 m/s. Swing angle of the insulator increases with θ and VH, and follows the law of sinθ when θ > 40°. The dynamic response component of the insulator’s swing angle is insignificant when VH > 30 m/s. The length of insulator tends to increase the transverse tension while decrease the swing angle of the insulator. In addition, the wind force coefficient from the aeroelastic model of the two-span conductors is smaller than that specified in GB50545 and GB50655, indicating that these two might overestimate the wind loads on multi-span multi-bundled conductors.

Dopant effect on Li+ ion transport in NASICON-type solid electrolyte: Insights from molecular dynamics simulations and experiments

The performance of sodium superionic conductor (NASICON)-type LiZr2(PO4)3 (LZP) solid electrolytes for Li-ion batteries is dependent on their ion transportation properties. Therefore, to achieve high stability, ionic conductivity, and good compatibility with Li, the LZP solid electrolyte has chosen and doped with Al to improve aforesaid properties. Also, the effect of the dopant on various parameters has been investigated via MD simulations and experimentally. In this study, molecular dynamics (MD) simulations were used to investigate the effect of Al doping on the ion transport properties of Li1+xAlxZr2−x(PO4)3 (LAZP, x = 0.0–1.0) solid electrolytes. A facile solid-state reaction was used to synthesize both pristine and Al-doped solid electrolytes and to estimate the effect of doping on the ionic conductivity and ion diffusion in LZP. Computational and experimental results provided strong evidence of improved ion conductivity and diffusion in LZP owing to the presence of the Al dopant. Furthermore, the computational results agreed well with the experimental results, thereby validating the computational model. A maximum ionic conductivity of σLi = 2.77 × 10−5 S cm −1 (for x = 0.2) was obtained. Enhanced ionic conductivity was observed with Al dopants owing to the creation of interstitial Li ions through a reduction in grain boundary resistance. However, a further increase in the amount of dopant reduced the ionic conductivity of LZP owing to Li-ion trapping at the most stable and metastable sites around the Al insertions. Doped LZP solid electrolytes are suitable for use in energy storage devices because of their enhanced ionic conductivity compared to that of pristine LZP.

Fault Diagnosis of Tower Grounding Conductor Based on the Electromagnetic Measurement and Neural Network

The performance of the tower grounding conductor is very important for the safe and reliable operation of the power transmission system. Under the current excitation, the grounding conductor in different states will produce different magnetic fields on the earth&#x2019;s surface. By measuring the surface magnetic fields, the fault types and location of the grounding conductor can be evaluated. However, the process of traditional manual analysis is extremely complex. This paper proposes a fault diagnosis method for tower grounding conductors based on deep learning to replace the manual diagnosis. The earth&#x2019;s surface magnetic field data-set generated by the grounding conductor consists of simulation data and experimental data. For practical application, the fine-tuning method is proposed to improve the diagnosis performance of the One Dimensional-Convolutional Neural Network (1D-CNN). Compared with the original 1D-CNN model, the results demonstrate that the proposed fine-tuning 1D-CNN has improved the diagnostic ability of the tower grounding conductor. For the six kinds of faults of rectangular tower grounding conductor, the average classification accuracy of the fine-tuning 1D-CNN model reaches 80.50% when only the classifier and dense connection layers are trained. The proposed method can be used in the fault diagnosis of tower grounding conductors, which has significant potential applications in detecting and maintaining tower grounding conductors.

Effect of Gd and Ti co-doping on electrical performance of Bi2O3 oxygen ion conductor

In this study, a new oxygen ion conductor electrolyte material with high conductivity was reported. Bi2O3 was co-doped with Gd2O3 and TiO2 by solid-phase synthesis method to obtain Bi1–3xGd2xTixO1.5+δ and Bi0.76Gd0.18−xTixO1.5+δ (TGSB) ceramics. The phase composition, surface morphology and electrical properties of TGSB samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM) and AC impedance respectively. XRD results show that only 6T12GSB has a single cubic fluorite structure, and impurity phases appear in other samples. The SEM results show that only when the doping concentrations of Gd and Ti are 12 mol% and 6 mol% respectively, the particle size is relatively smaller and there are no obvious pores. From the analysis of electrical properties, Gd dopant is helpful to the stability of the Bi2O3 phase than Ti dopant, but not beneficial to higher conductivity. When the doping concentration of Gd is higher than 16 mol%, it becomes more stable. The conductivity of the 6T12GSB sample is relatively high. The conductivity of the TGSB samples is higher than that of the TLSB samples under the lower temperature condition (<450 °C), and the electrical performance of Bi2O3-based materials are enhanced especially at low temperature.

Influence of Molecular Weight on the Organic Electrochemical Transistor Performance of Ladder-Type Conjugated Polymers.

Organic electrochemical transistors (OECTs) hold promise for developing a variety of high-performance (bio-)electronic devices/circuits. While OECTs based on p-type semiconductors have achieved tremendous progress in recent years, n-type OECTs still suffer from low performance, hampering the development of power-efficient electronics. Here, it is demonstrated that fine-tuning the molecular weight of the rigid, ladder-type n-type polymer poly(benzimidazobenzophenanthroline) (BBL) by only one order of magnitude (from 4.9 to 51kDa) enables the development of n-type OECTs with record-high geometry-normalized transconductance (gm,norm ≈ 11 S cm-1 ) and electron mobility × volumetric capacitance (µC* ≈ 26 F cm-1 V-1 s-1 ), fast temporal response (0.38ms), and low threshold voltage (0.15V). This enhancement in OECT performance is ascribed to a more efficient intermolecular charge transport in high-molecular-weight BBL than in the low-molecular-weight counterpart. OECT-based complementary inverters are also demonstrated with record-high voltage gains of up to 100V V-1 and ultralow power consumption down to 0.32 nW, depending on the supply voltage. These devices are among the best sub-1 Vcomplementary inverters reported to date. These findings demonstrate the importance of molecular weight in optimizing the OECT performance of rigid organic mixed ionic-electronic conductors and open for a new generation of power-efficient organic (bio-)electronic devices.

Effect of the build orientation on mechanical and electrical properties of pure Cu fabricated by E-PBF

Electrical conductors are usually made of pure copper because this material shows outstanding electrical conductivity (IACS > 100%). Additive manufacturing can be used to further improve the performances of such electrical conductors because it enables to consider sophisticated geometries impossible to be fabricated by conventional processing routes such as casting, machining or hot forming. In the present work, Electron Beam Powder Bed Fusion is optimized to achieve dense pure copper specimens (relative density >99.9%). Only few residual spherical pores inherited from the as-received powder particles are detected in the samples as nicely revealed by X-ray microtomography scans. Three different build orientations, namely 0{\textdegree}, 45{\textdegree} and 90{\textdegree} with respect to the build direction are produced. The microstructures are characterized using optical microscopy and EBSD measurements. The electrical conductivity is measured using the Eddy current method as well as the four-probes method while the mechanical properties are assessed using Vickers microhardness and tensile mechanical testing. The electrical and mechanical performances are discussed in the light of the microstructural characterizations, and further compared with a cold-worked Cu-ETP sheet subjected to an annealing treatment. It demonstrates that E-PBF is able to reliably produce components made of pure Copper whose properties equal those of pure copper fabricated by more conventional processing routes, regardless of the build orientation.

Transverse Stress Applying Technology for High-Current Superconducting Conductors Testing

High-current superconducting conductors are widely used in fusion magnets, high energy accelerators and high magnetic field facilities. It's urgent to carry out experimental research on DC performance of new conductors to meet the development needs of these magnets. A new test facility with maximum background magnetic field of 6 T and maximum sample current of 30 kA is developed. For the purpose of preventing the sample conductors from premature quenches due to mechanical disturbance under the magnetic field, it is necessary to apply a certain transverse stress to the sample through sample support. In this paper, two different kinds of transverse stress applying technologies, active method and passive method, are developed. The general design of these two kinds of sample supports, the influence of cooling and powering process on sample transverse stress with active sample support, the assembly gap analysis of passive sample support are described in detail. The used sample supports respectively for Nb-Ti Rutherford cable, MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cable-in-conduit Conductors (CICC) and Bi-2212 sub-cable testing are presented. Comprehensively considering the stability margin of conductor sample and the influence of transverse stress on performance of the sample, the selection basis of transverse stress applying at room temperature is also summarized.