HTS Tapes Research Articles

2G HTS tape and double pancake coil for cryogen-free superconducting magnet

The superconducting magnetic system (SMS) project is proposed. The second-generation high-temperature superconducting tapes for SMS are developed, fabricated and tested in NRC “Kurchatov Institute.” The magnet will be manufactured from non-insulated double pancake coils. Such a double pancake coil is manufactured and tested in liquid nitrogen. The integral radial resistance of this coil is determined.

The Effect of Shorted Secondary Circuit Material on Quench Protection of an HTS Tape Solenoid discharged across a Varistor

Studies suggest that an insulated ReBCO tape solenoid coil that is well-coupled inductively to shorted secondary can effectively be quench protected by discharging the coil across a constant voltage resistor. The discharge voltage across the constant voltage resistor is much lower than it would be for a constant resistance resistor that is used to achieve the same final quench temperature with or without a shorted secondary. How this quench protection works, depends on the constant voltage resistor characteristics, the properties of the shorted secondary circuit material and the amount of the material in the circuit. A previous paper suggests that the RRR shorted secondary circuit material is not important, which means that aluminum can be used in the secondary circuit and structural aluminum can support both the coil and the secondary circuit when that aluminum is on the outside of a solenoidal coil.

Delamination and current-carrying degradation behavior of epoxy-impregnated superconducting coil winding with 2G HTS tape caused by thermal stress

A thermo-mechanical-electromagnetic model is developed for estimating the delamination and current-carrying degradation of epoxy-impregnated pancake coils. The mixed-mode traction–separation law and the Weibull distribution of delamination strength are considered in simulating the onset and extension of the delamination caused by thermal stress. Because of the considerable differences in thermal shrinkage between the epoxy resin, insulation tape, and second-generation high temperature superconducting (2G HTS) tape, the accumulated radial thermal stress locally exceeds the electro-mechanical delamination strength and even the mechanical delamination strength. The electro-mechanical delamination strength of the 2G HTS tape is the transverse tensile or shear stress level corresponding to an abrupt irreversible critical current degradation. The mechanical delamination strength is the transverse tensile or shear stress limit corresponding to a structural failure. After injecting current into the coil, we obtained the E–I curve of the coil. The critical current and n-value of the superconducting coil indicate a strong degradation after epoxy-impregnation. The current-carrying degradation precedes delamination because the electro-mechanical delamination strength is smaller than the mechanical delamination strength. The degradation is more obvious in large than in small superconducting coils because the radial thermal stress is larger. The onset of degradation depends on the minimum delamination strength, suggesting that caution is required in screening the 2G HTS tape before winding the coil. The simulation results indicate that reducing the thickness of the insulation tape and the amount of epoxy resin effectively reduces the degradation of epoxy-impregnated pancake coils.

Cryo-stability of quasi-insulation winding method for hts coils regarding the width of insulation tape at over-current operation

According to growing demand for high power electric machines, HTS coils which are able to transport high current have been widely researched. For application of HTS coils to electric devices stable operation should be verified so that protection schemes of HTS coils have been investigated by many researchers. Among the many insulation methods for protection, the Quasi-Insulation (QI) winding scheme which improves thermal stability without charging-discharging delay has been proposed. The performance of the QI is affected by exposure area to coolant so that thermal stability depending on the width of the insulation tape should be considered. In this study, the magnetic characteristics and cryo-stability of the QI HTS coils using HTS tape according to the different width of the insulation tape were experimentally analyzed. A wider HTS tape (12 mm) was used to wind tested QI coils for transporting higher current, and QI coils with narrower insulation tape than half of the HTS tape were especially analyzed. The temperature estimation was also carried out to support the experimental results. Even though the width of insulation tape was narrower than an half of the HTS tape, field delay, generated field saturation and degradation were not observed from the experimental results. Therefore, the QI coil with narrower insulation tape can provide better thermal stability without any weaknesses of field generation so that the QI coil can be adopted in high current application such as SMES with higher operation margin.

Numerical Investigation on the Thermo-Mechanical Behavior of HTS Tapes and Experimental Testing on Their Critical Current

This work extends to second generation Rare-Earth Barium-Copper-Oxide ((Re)BCO) tapes an experimental procedure previously developed to analyze the impact of double bending at room temperature on the performance of Bismuth-Strontium-Calcium-Copper-Oxide (BSCCO) tapes. The modified procedure is applied to measure the critical current of a commercial (Re)BCO tape subjected to bending around a cylindrical mandrel first on one side, then on the other side, followed by the cooldown to cryogenic temperature. In the bending phase, mandrels of decreasing diameter are used to identify the minimum curvature leading to a significant reduction of the tape critical current. Furthermore, a novel finite element model is developed to complement the experimental results. The model simulates the double bending at room temperature, the following straightening of the sample, and its cooldown to cryogenic conditions. The coupled thermo-mechanical numerical model together with the temperature-dependent mechanical properties allow investigating the combination of thermal contraction effects and bending loads in the whole domain of the problem. The experimental and numerical results obtained help to give a better insight in the distribution of the strain and stress components inside the (Re)BCO tape and to evaluate their impact on the conductor electrical performance in relevant operating conditions.

Effect of Annealing on HTS Tapes with a Cerium Oxide Layer Inserted between the REBaCuO and Silver Layers

This paper presents extensive electrical, microstructural and chemical characterizations of HTS coated conductor samples in which an oxide layer (CeOx) has been added between the superconductor (GdBaCuO) and the silver (Ag) layers, in an attempt to increase the interfacial resistance between these two conductive layers. This increase of interfacial resistance is required to realize the current flow diverter (CFD) architecture in HTS tapes. All samples in this paper have been characterized before and after performing an annealing in oxygen atmosphere. The purpose of the annealing was to reduce the interfacial resistance generated by the CeOx layer, in order to achieve a proper value for the CFD architecture. Samples with different thicknesses of CeOx, namely 0, 10, 35 and 100 nm, have been produced and characterized. The critical current and the critical temperature have been measured to determine the quality of the superconducting layers, while cross-section transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) have been used to monitor the impact of the annealing. The results show a clear degradation of the superconducting layer for samples with a thick layer (≥ 35 nm) of CeOx after annealing at 450 oC. According to the EDS results, a reduction of the amount of barium is observed in the superconducting layer, which could explain the observed reduction of the critical current.

Electromagnetic Analysis on 2.5MJ High Temperature Superconducting Magnetic Energy Storage (SMES) Coil to be used in Uninterruptible Power Applications

Abstract In recent years, due to the digitization of the electrical devices electric load demand has been increased. Power security and stabilization are the other two challenges which necessitate the need of electrical energy storage. Along with the technological constraints, economical and environmental issues are the other challenges in the development of energy storage technologies. Fast response and high energy density features are the two key points due to which Superconducting Magnetic Energy Storage (SMES) Devices can work efficiently while stabilizing the power grid. Two types of geometrical combinations have been utilized in the expansion of SMES devices till today; solenoidal and toroidal. It has been found that the solenoidal arrangement is easier to fabricate and provides efficient approach to handle stresses produced by Lorentz forces. This work represents the development of 2.5MJ SMES solenoidal Magnet using 2G (SuperPower, YBCO having Tc=90K @ 0T) HTS tape. The effect of the operating current (passing through a single superconducting tape) has been evaluated. A reference magnetic flux of 3.5T has been considered in designing of HTS SMES. It has been found that the parallel fields for solenoidal magnet are large as compared to perpendicular fields which results into large magnitudes of Lorentz forces acting on HTS tape which may leading to structural instabilities and can cause failure. It has been concluded that higher currents can be used in order to lower down the total length of the superconductor as it can reduce the overall cost of the device

Effect of Annealing on HTS Tapes with a Cerium Oxide Layer Inserted between the Rebacuo and Silver Layers

Effect of Annealing on HTS Tapes with a Cerium Oxide Layer Inserted between the Rebacuo and Silver Layers

Анализ потерь в обмотках и стопках из ВТСП лент второго поколения

The model coil with the racetrack geometry based on second generation High Temperature Superconducting tapes has been developed for an electrical machine where a winding pack is a stack of 2G HTS tapes. It is important to evaluate transport current AC losses and possible methods to reduce them in a winding. In a device made of 2G HTS tapes, the main the AC losses are the hysteresis ones. Only numerical simulation permits to predict them in full. The FEM model for calculation of the hysteresis losses developed before for 2G HTS power cables was modified for a stack of the 2G HTS tapes in a coil. In this paper the methods to increase a computational speed are presented. Possible ways to reduce AC losses are discussed also. The details of the model and comparisons of calculations with measurements of the AC loss are presented.

I-V characterization of HTS tape under tensile stress using cryogenic UTM along with FEM analysis

I-V characterization of HTS tape under tensile stress using cryogenic UTM along with FEM analysis

Зависимость нагрева стабилизированных нержавеющей сталью токоограничивающих элементов на основе ВТСП-лент второго поколения от воздействия тока и параметров теплоотвода на границе с жидким азотом

Fault current heating of the current limiting modules made of 2G HTS tapes and stabilized with stainless steel was studied. It is demonstrated that the speed of current limiting element heating hardly depends on the degree of the stainless steel stabilization. The ways to improve the heat transfer with the help of the increase of the elements’ surface area were demonstrated with the use of a mathematical model taking into account parameters of heat transfer to liquid nitrogen.

Theoretical analysis of heat transport in tilted stacks of HTS tapes at temperatures above 20 K

Tilted stacks of HTS tapes show favourable properties in terms of magnetisation. Magnetised stacks can be applied in superconducting rotating machines. In such case they will be subjected to varying magnetic fields and heat generation will occur. Therefore it is important to understand heat transfer in anisotropic structure of a stack to avoid overheating and optimise the shape for maximum magnetisation.To analyse the heat transfer a computational procedure to find components of anisotropic thermal conductivity is developed and compared with existing experimental data. The material parameters ready to use in other analyses are provided. Anisotropy of the structure of the HTS tapes plays crucial role in definition of the thermal behaviour of the investigated elements.The thermal behaviour of the stacks with different angles of tilt is investigated with a numerical model. Results show that the geometry of the stack significantly affects heat transfer. Analytical formulas describing the thermal behaviour of the stack depending on its dimensions are developed. The method to increase the speed of calculations by homogenising the stack is presented and its accuracy assessed.

Nonequilibrium States in HTS Tapes under the Action of Short Current Pulses

This paper presents the results of studying the nonequilibrium processes in second generation HTS tapes under the action of pulsed current loads. In the study, we used short current pulses of various amplitudes from 0.9 to 5 values of the superconductor critical current. The minimum rise time of the current was 8 µs, and the pulse duration was from 1 to 250 µs. Comparisons in the behavior of samples under long current pulses with current rise time more than 3 ms were carried out. A qualitative difference in the formation of an nonequilibrium state during short and long current pulses was found. A stable current flow with amplitudes up to 4 times larger than the critical current was obtained without degradation of the superconductor. Experimental results were analyzed on the basis of the dynamic resistance model in the flux flow regime.

GdBCO (123) HTS 2G tapes superconducting characteristics investigation under the pulsed electron beam exposure impact

The 2nd generation composite HTS tapes samples based on the GdBCO (123) compound were irradiated in a pulsed electron accelerator (Terek-2 facility, IOF RAS) through a tantalum target to determine the thermal and shock loads effect at the tantalum-HTS boundary on the HTS tapes superconducting characteristics. Scanning Hall magnetometry was used to characterize the HTS samples after the electron irradiation exposure. The thermal modes and shock load in a composite superconductor under the irradiation influence are estimated depending on the magnitude of energy contribution to the target. At a silver surface temperature equal to the melting temperature, the critical current value drops by 87% of the initial value. At lower energy, a weaker critical current decrease was observed. The temperature effects and shock waves roles under the irradiation is discussed.

Optimization of wire construction from several 2G HTS tapes

Despite the second generation HTS tapes (2G HTS tape) have limits in critical current value, scientific and electric devices require more current density day after day. These requirements are realized by using different superconducting wires that consist of 2G HTS tapes designed in various combinations. Authors of this paper have developed the numerical model for estimation of total critical current in the superconducting wire and critical current in each 2G HTS tape placed in this superconducting wire. The current drop in six 2G HTS tapes having different constructions was analyzed. The result of this research is the decrease of critical current up to 25 % for the stack of tapes and up to 5 % for the parallel tapes in the same plane. In addition, what was also made is the estimation of the current distribution by length for six 25 m 2G HTS tapes in different constructions and determination of current deviation by length of the wire.

Analysis of Recovery Time of HTS Tapes With Electrical Insulation Layers for Superconducting Fault Current Limiters Under Load Conditions

The implementation of superconducting fault current limiters (SFCL) in the electrical power system requires the coordination of its parameters with the installed power system protection (PSP), in particular when using automatic reclosing (AR). The crucial parameter for AR is the recovery time of the SFCL, understood as the SFCL return time to the superconducting state after its operation. This time will depend mainly on the efficiency of the cooling system and the heat dissipation processes in the electrical insulation system. This article presents the results of experimental research on the return time to the superconducting state of superconducting tapes with layers of electrical insulation of various thicknesses. The tests were carried out in conditions in which the density of energy generated during the surge current flow correspond to the operating conditions of superconducting material in SFCL. Also, the transfer of this energy to liquid nitrogen corresponds to phenomena occurring in SFCL. The recovery time of several types of high temperature superconducting tapes in the zero current state and recovery under load were determined. The range of the load current at which it is possible return to the superconducting state was determined for tapes with and without electrical insulation. It has been shown that the analysis of these processes must take into account the strong dependence between the thermal energy transfer from the sample surface to liquid nitrogen and the type of nitrogen evaporation process on the surface of the sample. The presented research results are of particular importance for the functionality of SFCL and its cooperation with the PSP.

AC losses in the development of superconducting magnetic energy storage devices

Abstract AC losses are inevitable to be considered for effective design of Superconducting Magnetic Energy Storage (SMES) devices using High Temperature Superconductors. Various analytical techniques are available to estimate these AC losses however not sufficient to accurately predict the same. Hence, computational methods are being widely used in the prediction of AC losses as the experimental techniques are complicated to be implemented. YBCO (Tc = 90 K @ 0T) and BSCCO (Tc = 110 K @ 0T) are generally used in the construction of SMES. However, the critical temperature reduces as the external magnetic field is experienced by the tapes increases giving lower temperature margin for cooling purposes. In the present work, Computational Electrodynamics is used to predict the AC losses in Second Generation HTS tapes used in constructing the SMES. These losses which are dissipated as heat must be balanced by the cooling the requirements. The effect of external magnetic field on the degradation of critical current is examined. Finite Difference Time Domain approach is used for discretization of governing equations in solving for the AC losses. Further, electric field distribution in coated conductors due to the applied magnetic field is investigated. Hence, the results of the present analysis guide the thermohydraulic design of SMES devices.

The dynamic processes in second generation HTS tapes under the pulsed current and magnetic impact

This paper presents the results of complex multiphysical modelling of non-equilibrium states arising in high-temperature superconducting composites under current, magnetic, and combined control switching impacts types. The simulation and analysis of the dynamics of electrophysical and thermal processes occurring in the HTS composites layered structure taking into account the influence of local thermal processes in the composite structure, in particular, heat generation bursts during a pulse, has been performed. The HTS composite switching times from the superconducting to the normal state have been investigated for various current pulses amplitudes in homogeneous magnetic fields. An experimental verification of the numerical model has been carried out.

Current caring capacity of bare REBCO tapes at high ramp rates at 77 K and 4.2 K.

In this paper we present the results of an experimental investigation of single 12 mm REBCO tapes as well as soft-soldered 5-folded REBCO stacks at current ramp rates up to 320 kA/s. Experimental ring-samples made of one or five HTS tapes with joints were manufactured and charged in external magnetic field. The experiments performed at 77 K showed that the current caring capacity of the samples is very weakly affected by transport current ramp rate. No transitions to the normal state were observed in liquid nitrogen at external magnetic field ramp rates up to 8 T/s. The maximum transport currents achieved by the samples were limited by the thermal equilibrium with the coolant. In contrast, at 4.2 K both single and stacked samples demonstrated preliminary quenches caused by the origination of local defects in the superconducting layers of the HTS tapes with resistances of about 1 µOhm at 4.2 K. Reexamination of the damaged samples at 77 K showed that at ramp rates higher than 200 kA/s the currents of the thermal equilibrium with the coolant appeared to be the same before and after the defects appearance.

Numerical simulation of the fast processes in HTS tapes under the pulsed current load

This paper presents a numerical layered 2G HTS tape model with the transport current flowing through it. The simulation is performed by using FEM H-formulation method implemented in the Comsol Multyphysics software. The model provides two cooling modes: cryocooler and liquid nitrogen. LN2 cooling mode provides for a complex hysteresis character of the liquid nitrogen boiling curve and the boiling regimes changing possibility between the stationary and the bubble boiling. The delay of the voltage rising with a transport current above the critical value pulse input is shown in the liquid nitrogen cooling case. The possibility of parameters calculating for current redistribution from the HTS to the stabilizing copper layer is shown, and the stabilizing coating thickness effect on the thermal transition critical current value is studied A comparison with experimental results is carried out.