Straight Tapes Research Articles

Fast Quench Detection in SFCL Pancake Using Optical Fibre Sensing and Machine Learning

A fast hotspot detection technique has been implemented and patented at École Polytechnique Fédérale de Lausanne (EPFL) under the European Union project FastGrid. The optical fibre sensing based technique uses the Mach-Zehnder Interferometer (MZI) and can detect even singular hotspots in the superconductor within 15ms. The MZI setup is very sensitive to external perturbations and mechanical stresses, which can manifest in the output along with the response to hotspots. The disturbance the setup is subject to, varies with the sample being tested and the environment it is being tested in. For example, the sample length and configuration, in addition to the routing of the optical fibre can determine the extent of the stresses on the optical fibre. Previous publications, showcased experiment results on relatively simple sample configurations which were straight HTS tapes with short lengths (0.3m or 1m). This manuscript will investigate the technique feasibility for a more complicated sample type: a pancake prototype for a superconducting fault current limiter (SFCL), comprising 12m of HTS tape in a bifilar winding, with taped optical fibre along the length of the conductor. The manuscript will also give a brief overview of a machine learning based post processing technique for the experimental data, developed at EPFL to supplement the MZI based quench detection for easy and reliable quench detection in large scale applications.

Enhanced critical axial tensile strain limit of CORC® wires: FEM and analytical modeling

Conductor on Round Core (CORC®) cables and wires are composed of spiraled high-temperature superconducting (HTS) rare-earth barium copper oxide (REBCO) tapes, wound in multiple layers, and can carry very high currents in background magnetic fields of more than 20 T. They combine isotropic flexibility and high resilience to electromagnetic and thermal loads. The brittle nature of HTS tapes limits the maximum allowable axial tensile strain in superconducting cables. An intrinsic tensile strain above about 0.45% will introduce cracks in the REBCO layer of straight HTS tapes resulting in irreversible damage. The helical fashion at which the REBCO tapes are wound around the central core allows tapes to experience only a fraction of the total axial tensile strain applied to the CORC® wire. As a result, the critical strain limit of CORC® wires can be increased by a factor of more than 10 that of REBCO tapes. Finite element (FE) and analytical models are developed to predict the performance of CORC® wires under axial tensile strain. A parametric analysis is carried out by varying the winding angle, the Poisson’s ratio of the CORC® wire core, the core diameter, and the tape width. The results show that a small variation in winding angle can have a significant impact on the cable’s axial tensile strain tolerance. While the radial contraction of the helically wound tapes in a CORC® wire under axial tensile strain depends on its winding angle, it is mostly driven by the Poisson’s ratio of the central core, affecting the tape strain state and thus its performance. Contact pressure from multiple layers within the CORC® wire also affects the CORC® wire performance. The FE model can be used to optimize the cable design for specific application conditions, resulting in an irreversible strain limit of CORC® cables and wires as high as 7%.

Hydraulic Resistance of Flows in Tubes with Inserted Straight and Twisted Tapes

The results of an experimental study of hydraulic resistance of a laminar flow with air stream macrovortices in a long tube with inserted straight and twisted tapes are presented. It was found that there is a minimum in the relationship of the hydraulic resistance coefficient with the rotation pitch of the tape inserted into the tube. An empirical equation, recommended for use in a wide tape rotation pitch variation range, has been derived for calculating hydraulic resistance.

Magnetization Loss Estimation of HTS Solenoid Coils Wound With CORC

CORC is one of the candidates of the HTS cable for high field magnets. We have been interested in applying CORC to HTS power transformers that require not only large currents but also very low AC losses. Striation and twisting are the solutions for reducing AC losses. We suggested an estimation method for a rough calculation of magnetization losses in a striated CORC coil. First, we measured and calculated the magnetization losses of short samples of straight CC tapes and CORC. Before considering the striation effect, we analyzed the characteristics of slit HTS tapes. In order to emulate the slitting of an HTS tape, we prepared three kinds of HTS tapes with different widths: 2, 4, and 6 mm. Slitting will certainly create the effect of reducing the magnetization loss, but the effect is not directly dependent on the number of the slits nor the applied field magnitude. We measured and compared the magnetization losses of a wide HTS tape to those of narrow HTS tapes. And the narrow tapes were arranged in parallel and measured, so the net width was same as the width of the wide tape. Finally, we applied the measured data of the magnetization loss of several samples to the calculation of the losses of solenoid coils wound with CORC in order to take into account the loss reduction effect of slit HTS tapes.

Enhancing the thermal performance of AL2O3/DI water nanofluids in micro-fin tube equipped with straight and left-right twisted tapes in turbulent flow regime

ABSTRACTThis article communicates the thermal performance, heat transfer rate, and friction factor of Al2O3/DI water nanofluids at different concentrations in a micro-finned tube with tube helical inserts for different twist ratios. The thermal performance, heat transfer coefficient, and friction of the present study is also compared with a plain tube for validation. From the study, it is identified that the micro-finned tube with tube insert performance is higher as compared with a plain tube. Similarly, an empirical relation for Nusselt number (Nu) and friction factor (f) is estimated for straight twisted tube and left-right combination. The deviation between experimental and theoretical values for left-right twist and straight twist is found as 3 and 7% for Nusselt number and 7 and 9% for friction factor, respectively. Similarly, while analyzing the thermal performance, it was found that the maximum performance achieved was with a micro-fin tube with left-right twist with nanofluid concentration of 0.2%.

Development of a Novel Ablative Composite Tape Layup Technology for Solid Rocket Motor Nozzle and Liquid Engine Liners

Solid rocket motor nozzles and liquid engine throats use ablative composite materials to protect the structures from the extremely severe operating conditions of high temperature, pressure and particle impingement. These ablative nozzle liners are processed from carbon phenolic/silica phenolic prepregs using a complex processing cycle. The process starts from impregnating the fibres with phenolic resin followed by either moulding or wrapping/winding prepreg tapes over metallic mandrels followed by polymerization under pressure. Traditionally, prepreg is cut into straight tapes and wound on mandrels to form the divergents. For throats and convergents, prepreg patterns are cut and stacked for curing. Plies of shape conforming to the development of base cone are cut from the prepreg and wound on the mandrel. After polymerization, the final required configuration is machined from this cylindrical blank after the liners are cured. The new method, described in this paper, replaces the straight-cut prepreg tapes by bias-cut prepreg tapes. These can be used for ablative liners in which the plies are at an angle to the direction of the flow. Bias tapes are cut at 45° to the warp and weft directions of the fabric to the required width and formed to the required frustum of cone. Since the cone is formed from straight cut bias tape, the fibre construction will be uniform around the circumference unlike the pattern cut tape. The efficiency of this process depends on the wrapping ratio which is in turn a function of the diameter, ply angle and tape width. To get the best wrapping ratio, shaped mandrels are used which brings down the material wastage and machining allowances. This paper describes the attempts to develop the Bias wrapping technology for angle wound liners. The details of process trials, challenges faced and how they were overcome, advantages of the process over conventional process etc are explained. Exhaustive material characterization of the material was done. Property comparison and validation of performance in subscale tests and a full scale static test are also discussed. The analysis indicates that this new technology has good potential in replacing the traditional tape-winding technology for rocket motor nozzle liners.

Three-Dimensional Numerical Simulations of Twisted Stacked Tape Cables

Different magnet applications require compact high current cables. Among the proposed solutions, the Twisted Stacked Tape Cable (TSTC) is easy to manufacture and has very high tape length usage efficiency. In this kind of cables the tapes are closely packed, so that their electromagnetic interaction is very strong and determines the overall performance of the cable. Numerical models are necessary tools to precisely evaluate this interaction and to predict the cable's behavior, e.g. in terms of effective critical current and magnetization currents. For this purpose, we developed a fully three-dimensional model of a TSTC, which not only takes into account the twisted geometry of these cables, but is also able to account for the contact resistances of the current terminations. The latter can have profound influence on the way the current is partitioned among the tapes, especially on short laboratory prototypes. In this paper, we first use the numerical model to compute the critical current and the magnetization AC loss of a twisted tape, showing the differences with the case of a straight tape. Then, we use it to calculate the current distribution in a TSTC cable, comparing the results with those experimentally obtained on a cable composed of four straight stacked tapes. The results show the ability of the model to simulate twisted conductors and constitutes a first step toward the simulation of TSTC in high-field magnet applications. The presented modeling approach is not restricted to the TSTC geometry, but may be used for any cable configuration with periodical translational symmetry.

Critical state solution of a cable made of curved thin superconducting tapes

In this paper, we develop a method based on the critical state for calculating the current and field distributions and AC losses in a cable made of curved thin superconducting tapes. The method also includes the possibility of considering spatial variation of the critical current density, which may be the result of the manufacturing process. For example, rare-earth-based coated conductors are known to have a decrease in transport properties near the edges of the tape: this influences the way the current and field penetrate the sample and, consequently, the AC losses. We demonstrate that curved tapes arranged on a cylindrical former behave as an infinite horizontal stack of straight tapes, and we compare the AC losses in a variety of working conditions, both without and with the lateral dependence of the critical current density. This model and subsequent similar approaches can be of interest for various applications of coated conductors, including power cables and conductor-on-round-core cables.

Anew layout of HTS tapes and their critical currents for DC power cables

Weinvestigated thegapeects on the critical current of the middle tape in the paralleled arrangements of three straight BSCCO tapes with monolayer, 2-layer and 3-layer structures to improve the cable superconducting performance by the tape arrangement. The critical current of the BSCCO tape increases with the decreasing of thegap for the monolayer structure, increases by 11% for the 2-layer and decreases by 15% for the 3-layer structure. Anew layout of HTS tapes for the DC power cable is presented. The critical current of the BSCCO tape in a cable with a new layout may increase by 10%.

Normal Zone Propagation in 2-Dimensional YBCO Winding Pack Models

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

Phase Shifts of Parallel Currents in a Single-Layer Model of Superconducting Cables

To reach large current carrying capability and mechanical flexibility, superconducting cables consist of many single conductors connected in parallel. Distribution of ac current into these parallel paths is controlled by their impedances, which often are not identical. We have found that, even in the case of a cable model made from straight Bi-2223 tapes placed in just one single layer, the nonuniformity of contact resistances causes a dispersion in the amplitudes and phases of ACs in individual tapes. Two models, one analytical and other a Finite Element Model, were used to predict the influence of phase shifts on ac loss and its measurement by an electrical method. Due to phase shifts of local magnetic fields, the purely inductive component of voltage taken by an arbitrary pair of taps is not exactly out-of-phase regarding the total cable current. Then, its product with the cable current is evaluated as a false loss-contributing component. Fortunately, with the use of voltage taps and wires regularly distributed around the cable, true value of ac loss can be recovered.

AC Losses in Long Bi-2223 Tapes Wound Into a Solenoidal-Coil

Electrical loss-measurements were carried out in liquid nitrogen for long Bi-2223 tapes wound into a solenoidal-coil under various external conditions of ac transport currents and ac magnetic fields. In this experiment a new measuring-system, which is an extension of our original measuring-system applicable to short and straight HTS tapes, was developed. In this new system, the Poynting vectors at the outer and the inner surfaces of the sample coil were measured to get ac loss values by using two movable sets consisting of both a potential lead pair and a pick-up coil on each surface of the coil; The moving direction is the coil axis and its distance is one pitch of coil windings. Several samples were prepared in order to clarify fundamental electromagnetic-properties of Bi-2223 coils with various windings. The obvious difference of loss properties among these samples was observed for some external conditions of ac transport currents and ac magnetic fields.

Poynting vector method: AC loss measurement of long HTS tapes or wires wound into a solenoidal-coil

A new electrical system was developed for measuring ac losses of long HTS tapes or wires wound into a solenoidal-coil. This coil-loss measuring-system is an extension of our original ac-loss measuring system that is applicable to short, straight HTS tapes under various external conditions of transport currents and transverse magnetic fields, and is useful for fundamental studies of various windings of practical multi-layered coils. In this new system, the Poynting vectors at the outer and the inner surfaces of the coil were measured to get ac loss values by using two movable sets consisting of both a potential lead pair and a pick-up coil on each surface of the coil. The moving direction is the coil axis and its distance is one pitch of coil windings. The value of ac losses can be obtained by summation of the Poynting vector at many positions during the movement. The applicability of this system was confirmed by ac loss measurements on a solenoidal-coil wound loosely with Ag-sheathed, multifilamentary Bi-2223 tapes.

C241 スリットを有する物体の抗力特性に関する研究

This paper describes experimental result of drag characteristics of the object with the slit. The test pieces are the column that the slit of straight, Y-type slit and clearance tapes were installed for the spiral rolls at 45. Slit width, Y-type opening angles, pitch of the spiral roll were changed. The Reynolds number is 60000. Using the smoke wind-tunnel facility, the flow visualization experiment processes image by the digital camera by the computer after the photographing.

Characterisation and modelling of HTS coils

Recent efforts on manufacturing high temperature superconductors (HTS) have resulted in the production of coils which promise significant benefits for power engineering applications. Losses in two HTS pancake coils carrying AC current are measured and the results are analysed. It is shown that a thin pancake coil with relatively large diameter can be treated as straight tapes arranged in a face-to-face stack with the spacing between the tapes chosen to be relatively small. Losses in the tapes become those predicted using Norris's equation for an infinite slab.

Crystal engineering using very short and linear C(sp)–H⋯N hydrogen bonds: formation of head-to-tail straight tapes and their assembly into nonlinear optical polar crystals

The crystallization of 4-ethynylpyridine (1) and 4-(4-ethynylphenyl)ethynylpyridine (2) leads to C(sp)-H⋯N hydrogen bonded straight tapes that further assemble into polar crystals, in the case of 2, and show intense powder SHG response, 8 times more efficient than crystalline urea.

ポインチングベクトル法による高温超伝導テープ線材の交流損失測定

A new system was developed for measuring losses electrically in short, straight HTS tapes under various external conditions of transport currents and transverse magnetic fields. In this method, Poynting vectors around the straight sample were measured to get loss values by using two movable sets consisting of both a potential lead pair and a miniature pick-up coil on each flat face of the tape. In order to confirm validity of this system, loss measurements on short samples of Ag-sheathed Bi2223 multifilamentary tapes were carried out in liquid nitrogen for three cases as simultaneous sweep of ac transport currents and transverse ac magnetic fields and two single sweep cases of one of them. The results obtained show that this is extremely useful for measuring these ac losses as long as longitudinal change in the magnetic field can be neglected.

Relationship between Morphology and Na+ Content of Langmuir-Blodgett Mesoscopic Tapes Induced by a Change of pH

Abstract Langmuir-Blodgett (LB) films of a short chain carboxyazobenzene derivative on mica exhibit nearly straight tape structures 1 nm thick, 80 nm wide, and over several μm long at pH 7.0. Lowering pH causes the tapes to be wavy and irregular without coagulation. The fraction of straight tapes at a constant salt concentration increases smoothly till pH 7, then drops sharply. Above 8, no transfer occurs. The fraction of Na per molecule in the film also increases with pH and becomes 0.5 at pH 7. The wavy tapes are found to become straight even with a slight ionization. An importance of the charge distribution rather than the total charge density is suggested.

Field-free core, current distribution, and alternating current losses in self fields for rectangular superconductor tapes

A method is proposed to calculate the shape of field-free core, the current distribution, and accordingly the alternating current (ac) losses in self fields as a parameter of current amplitude I0 for straight superconductor tapes with the arbitrary sectional geometry. The validity for this is justified by showing that magnetic fields inside the field-free core are negligibly small and by checking that calculation results of ac losses for elliptic tapes agree with the prediction by the theory of Norris. The ac losses for rectangular tapes behave as a thin strip superconductor in high I0 values near critical current, while showing a gradual deviation from this behavior as I0 is lowered. A decrease in the aspect ratio of width to thickness in the rectangular tape makes the deviation more remarkable.

The coupling impedance of tape structures

A periodic array of parallel straight tapes is considered. This can propagate a variety of TEM waves, each one corresponding to a different mode of excitation of the tapes. The case in which there is simply a fixed phase-change from one tape to the next is treated in detail. The exact field distribution is determined by using the theory of analytic functions of a complex variable. It is applied to the calculation of the coupling impedances and dispersion curves of tape helices, ladder lines, interdigital lines and meander lines. The calculations show that, with certain provisos, the product of the coupling impedance and the group velocity is the same for all these structures when they have the same tape length, tape width and gap width. The tape length is to be interpreted as the length of one turn in helices and the length of half a turn in meander lines. The provisos are as follows: the phase-change coefficient must be the same in each case; the coupling impedance must be evaluated at the array in helices, averaged over the array in ladder lines and evaluated at the centre lines of the array in interdigital and meander lines; finally, the ladder lines considered must be slightly perturbed easitron structures. Averaging over the array in helices does not alter the coupling impedance. Averaging over the array in interdigital and meander lines reduces the coupling impedance by a factor between 0.5 and 1. In a strongly perturbed easitron structure, the product of the average coupling impedance at the array and the group velocity differs from that in a slightly perturbed easitron structure by a factor for which an approximate formula is given. The use of tape structures in travelling-wave tubes for the millimetre wavebands is discussed briefly.