2G High Temperature Superconducting Research Articles

The Effect of the Interfacial Resistance of the Superconducting-stabilizer Film on the Typical Sector Diffusion Pace for 2G HTS Tapes

High temperature superconducting (HTS) tapes of the second generation have been widely used as energy storage materials, such as in superconducting magnetic energy storage (SMES) devices. In order to enhance the current-carrying characteristics, these systems are typically run close to the critical currents of the coated conductors; as a result, hot spots may develop, which could cause the superconductor to become quenched. In order to prevent the start of hot spots and to reduce the amount of faulting, efforts have been made to raise the normal zone propagation velocity (NZPV) in this manuscript. The interfacial resistance between the superconductor and stabilizer layer, which can act as a current flow diverter during fault circumstances, has been shown to be the key to producing massive NZPV. The tape's architecture has been slightly modified by the addition of a high resistive layer between the superconducting and stabiliser layers, where various interfacial resistances have been utilised to forecast the temperature distribution between 10 cm lengths of HTS tape. A 2D numerical model was created using COMSOL to assess the NZPV and temperature distribution of the 2G superconducting tape. It has been concluded that larger NZPVs can be achieved by using substantial interfacial resistances to prevent superconducting tape quenching.

Comparative study of current carrying capacity between 1G and 2G HTS tape samples at different temperatures and magnetic fields

Two categories of high-temperature superconducting (HTS) tapes, the silver-sheathed BSCCO tape (1G HTS tape) and REBCO coated conductor (2G HTS tape), have been commercialized worldwide and widely used in applications. In this study, the 1G HTS tape produced by Sumitomo and 2G HTS tape produced by Superpower were selected for a systematic comparative study in critical current (I c) performances under various temperature and magnetic field conditions. The anisotropy and I c variation patterns of these two types of samples in the temperature range of 25–77 K, magnetic field from 0 to 7 T and field angle from 0 to 90° were compared and analyzed. The results of this study reveal certain comprehensive characteristic features of these two categories of HTS tapes, supplementing some new systematic information to the literature.

Experimental study on AC loss of 1G and 2G HTS coils with an identical structure, geometry and number of turns

Devices made of High Temperature Superconductor (HTS) will suffer AC loss during AC operations, which has unnegligible influence on energy consumption, overall efficiency, cooling cost, and operational stability of the devices. In this study, comparative measurements on 1G and 2G HTS coil samples with an identical structure, geometry, and number of turns were systematically conducted with a calorimetric method at different current values (I rmss) and frequencies (fs). The AC loss characteristics of the HTS samples were analyzed and compared based on the experimental results. The results show that eddy current and coupling play a more dominant role than magnetic hysteresis in the total AC loss of coils made of HTS tapes. The AC loss of both samples increases with I rms and f, but the AC loss is more sensitive to I rms than to f. Under the same conditions, the 1G coil sample has a slightly larger AC loss than the 2G one.

Design and investigation of losses of a low-current HTS AC cable for a promising cryogenic generation system

Currently, there are a large number of projects dedicated to electric machines aimed at use in the field of transport and equipped with windings made of high-temperature superconductors (HTS). These machines in their majority have rated currents significantly less than 1kA, which is a too low value for AC HTS cables in the power industry, where current values can reach up to 10kA. On the other hand, connecting, for example, an electric generator with cryogenic cooling and its load (which, most likely, will also have cryogenic cooling) with copper wires on board of a vehicle does not look like an effective solution. This article is devoted to the development of the concept of an alternating current transmission system for machines with a rated current of less than 1 kA through HTS cable. In order to achieve a compact design, it was decided to use a cable consisting of stacks of second-generation (2G) HTS tapes. A series of experiments was carried out with different numbers of tapes and directions of current in them for stacks of 2, 4 and 6 the HTS tapes. The results were compared with finite element modeling. The article shows that when current flows in adjacent cable HTS tapes in opposite directions, like as in bifilar windings, it is possible to achieve a significantly lower level of losses per tape than when current flows in the cable tapes in one direction.

Experimental investigation of axial tensile and fatigue behaviors of HTS round strands

For the development of high-temperature superconducting (HTS) magnet systems of future fusion devices, a novel HTS round strand based on a stacking structure was designed and manufactured using second generation (2G) HTS tapes. Different mechanical loads during operation can result in irreversible degradation of the strand. The axial tension and fatigue loads need particular attention. Therefore, it is important to investigate the electromechanical behavior of the round strand under various axial tension and cyclic loads. In this paper, the axial tensile and fatigue tests were conducted at 77 K, self-field. Taking 95% critical current (Ic) retention as the criterion, the results of the tensile tests revealed that the average tensile stress and strain were as high as 344 MPa and 0.47%, respectively. Fatigue characteristics were also investigated as a function of axial tensile stress. No significant performance degradation was observed up to 100,000 loading cycles with stress amplitudes ranging from 20 MPa to 200 MPa. Ic degradation occurs after 16,000 loading cycles with 380 MPa as the maximum stress. Furthermore, the microscopic defects of the round strand samples due to fabrication imperfections and mechanical loading were investigated using metallographic microscope and scanning electron microscope. These results presented in this paper are useful for comprehending and improving the mechanical behaviors of the strand in high-field and large-scale fusion magnet systems.

Operation of Prototype Race-Track Closed-Loop HTS Coil With Metal-as-Insulation in Solid Nitrogen

The second generation (2G) high temperature superconductor (HTS) has excellent current-carrying density performance in strong magnetic field. Thus, the maglev system driven by 2G HTS magnets has been studied a lot. In the design of magnets, metal-as-insulation coil retains self-protection feature of the no-insulation coil, and it performs well in charging time. On the other hand, using solid nitrogen (SN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) as a “thermal battery” may effectively reduce the volume of on-board HTS magnets. In order to design on-board magnets with fast charging, small volume and self-protection, firstly a prototype coil was manufactured. Then the experiment apparatus was set up and experiments in the persistent current mode were carried out. It was obtained by fitting that the magnetic field decay rate of the prototype coil was about 0.24% per day. This paper provides a foundation for the production of real-scale on-board magnets cooled by SN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .

HTS Tape Mechanical Behavior Sensitivity on Material Properties and Thickness of Material Layers

Multilayer 2G high-temperature superconductor (HTS) tapes undergo various mechanical loading steps as part of a superconducting magnet operation. The mechanical loading steps include cool-down to cryogenic temperatures and Lorentz forces when powering up the magnets. Studying the mechanical behavior of the constituent layers in a HTS tape can reveal the strain or stress level in each layer and help in predicting the probability of mechanical failure or critical current degradation. A detailed finite element method (FEM) -based simulation models enable us to estimate the mechanical behavior in each layer. However, defining the model parameters for material mechanical properties or thickness of each material layer can have consid-erable uncertainty due to variation in manufacturing processes and missing measurements of material properties within these tapes. The material properties in thin layers may not exactly comply with bulk materials of the same kind. In this paper we present a sensitivity analysis for mechanical behavior dependence on material properties variation in the constituent layers of a HTS tape. The results give important insight about the accuracy and reliability of mechanical simulation results and guide the priorities in future material characterization. In addition, we will investigate the effect of the thickness of Hastelloy layer on effective macroscopic mechanical behavior of the tape. A nonlinear elastoplastic FEM model is used for performing the simulations.

Deterioration of the 2G HTS tapes by the Ne+ ions irradiation (250 keV)

We discuss changes in properties of Gd-based high-temperature superconducting (HTS) tapes induced by 250 keV Ne+ ions irradiation. HTS tapes are used in devices operating in extreme radiation conditions with the prospect of using them in space industry. Ionizing radiation, including heavy ion bombardment, can introduce defects (e.g. Schottky, Frenkel ones) to the microstructure of tapes, leading to deterioration of the superconducting parameters. Therefore, the superconducting layer of the tape was implanted with fluences from 1012 to 1014 Ne+/cm2 to determine the cosmic ray irradiation effect. Comprehensive studies of the microstructural, structural, magnetic, and electrical properties of the irradiated tapes prove the microscopic origin of their deterioration. It is mainly due to oxygen deficiency and microstructural as well as structural defects. The critical current densities are reduced by 33% – 60% (depending on the external magnetic field) compared to the reference sample.

Design and Characteristic Analysis of an Axial Flux High-Temperature Superconducting Motor for Aircraft Propulsion.

In line with global environmental regulations, the demand for eco-friendly and highly efficient aircraft propulsion systems is increasing. The combination of axial flux motors and superconductors could be a key technology used to address these needs. In this paper, an axial flux high temperature superconducting (HTS) motor for aircraft propulsion was designed and its characteristics were analyzed. A 2G HTS wire with high magnetic flux characteristic was used for the field winding of the 120 kW axial flux HTS motor, and the rotational speed and rated voltage of the motor were 2000 rpm and 220 V, respectively. The axial flux HTS motor implements a revolving armature type for solid cooling of the HTS field coil. The electromagnetic and thermal features of the motor were analyzed and designed utilizing a 3D finite element method program. The HTS coil was maintained at the target temperature by effectively designing the current lead and cooling system to minimize heat loss. These results can be effectively used in the design of propulsion systems for large commercial aircraft in the future as well as for the design of small aircraft with less than 4 seats.

Design and Analysis of Cryogenic Cooling System for Electric Propulsion System Using Liquid Hydrogen

As the demand for eco-friendly energy increases, hydrogen energy and liquid hydrogen storage technologies are being developed as an alternative. Hydrogen has a lower liquefaction point and higher thermal conductivity than nitrogen or neon used in general cryogenic systems. Therefore, the application of hydrogen to cryogenic systems can increase efficiency and stability. This paper describes the design and analysis of a cryogenic cooling system for an electric propulsion system using liquid hydrogen as a refrigerant and energy source. The proposed aviation propulsion system (APS) consists of a hydrogen fuel cell, a battery, a power distribution system, and a motor. For a lab-scale 5 kW superconducting motor using a 2G high-temperature superconducting (HTS) wire, the HTS motor and cooling system were analyzed for electromagnetic and thermal characteristics using a finite element method-based analysis program. The liquid hydrogen-based cooling system consists of a pre-cooling system, a hydrogen liquefaction system, and an HTS coil cooling system. Based on the thermal load analysis results of the HTS coil, the target temperature for hydrogen gas pre-cooling, the number of buffer layers, and the cryo-cooler capacity were selected to minimize the thermal load of the hydrogen liquefaction system. As a result, the hydrogen was stably liquefied, and the temperature of the HTS coil corresponding to the thermal load of the designed lab-scale HTS motor was maintained at 30 K.

Numerical Analysis on Performances of Critical Current for Rutherford Cable Made From HTS Quasi-Isotropic Strands

2G high temperature superconducting (HTS) tapes are frequently cabled into strands that can be assembled as conductors in cables with various layouts and thus potentially employed in large-scale superconducting magnets with high magnetic fields and large transport currents. One option meeting the requirements for manufacturing high-current cables is the Rutherford cable configuration. This article proposes a flat Rutherford cable with a copper core made up of 12 quasi-isotropic strands. The critical current characteristics of the Rutherford cable are numerically analyzed at 77, 20, and 4.2 K by using the finite element method and a self-consistent model in self-field and applied magnetic fields with different magnitudes and orientations, respectively. Additionally, the simulated results of the Rutherford cable are compared with those of a directly stacked conductor. The results show that the proposed Rutherford cable can attain critical currents in the hundreds of kA range at 20 and 4.2 K in high fields. This Rutherford cable design is a potential and prospective solution for high-current superconducting cables in power transmissions and large-scale magnets with a high magnetic field.

Dependence of dynamic resistances in high-temperature semiconducting quasi-isotropic strands on magnitude and orientation of AC magnetic field

The dynamic resistance of a superconductor appears if it carries a direct current (DC) current and is simultaneously exposed to alternative current (AC) magnetic fields if its amplitude is higher than its full penetrated field. Due to its strong anisotropy, the dynamic resistance of high-temperature superconducting (HTS) tape is not only affected by the magnitude of AC magnetic fields but also their orientations. In particular, the dynamic resistance has considerable effect on the current distribution in HTS cables (except for Roebel cables) and even cable-in-conduit conductors made from those HTS cables, except for dissipative loss. This paper presents the behavior of dynamic resistance in an HTS quasi-isotropic strand (Q-IS), which consists of four sub-stacked 2G HTS tapes proposed by our group at North China Electric Power University, while it carries a DC current and simultaneously experiences an AC magnetic field with different magnitudes and orientations. An angular dependence of dynamic resistance in a single 2G HTS tape in an AC magnetic field with various orientations is first performed in simulations and experiments, respectively. The experimental results are in good agreement with the simulated ones, which shows that the dynamic resistance of a Q-IS also exhibits quasi-isotropic characteristics and has an important effect on the distribution of DC transport current. The related results are promising for the design and application of other DC HTS cables, feeders and magnets.

Numerical Studies of Dynamic Characteristics of a Stack-Type HTS Maglev System Based on H-Formulation

High temperature superconducting (HTS) magnetic levitation (maglev) is a promising technology for future high-speed transit systems. Superconducting magnetic bearings are made of a permanent magnet guideway and HTS bulks (bulk-type) or stacks of 2G HTS tapes (stack-type). If the dynamic behavior of bulk-type HTS maglev systems has been well reported, there is little literature about the dynamics of stack-type HTS maglev system. To fill the gap, we built here an electromagnetic-mechanical model of a stack-type bearing. We used a segregated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -formulation finite element model to account for the nonlinear resistivity. The multi-layer structure of the HTS tape is either homogenized or modeled in detail. We studied the bearing dynamic response when subjected to different time-varying external magnetic fields mimicking the guideway irregularity and the vehicle speed. The results show that the induced current in the copper layer negatively impacts the stability. By extension, since it cannot account for the copper layer, the homogenized model is not suitable for such analysis. This work contributes to finding viable measures for improving the stability of stack-type HTS maglev systems.

Progress Towards a REBCO Homopolar Motor With the Gallium-Indium-Tin Sliding Contacts

Development of homopolar electric machines is a promising superconducting application. A homopolar motor with a 2G high-temperature superconducting (HTSC) magnetic system and copper disk rotor is designed at the NRC “Kurchatov Institute”. The advantages of such electric machines are considered. The liquid metal sliding contacts based on a gallium-indium-tin alloy are considered as a safe alternative to toxic mercury or NaK alloys. The homopolar motor controlling by a proportional-integral-differentiating (PID) algorithm is simulated and checked experimentally. The results of the preliminary tests of HTSC magnetic system and liquid metal contact are also reported.

36-5-3] Stabilizer에 따른 2세대 고온 초전도 선재의 전기적 열화특성

2G High temperature superconducting(HTS) conductors are usually considered as appropriate superconductors for a superconducting coil to develop an applied superconducting apparatus such as a superconducting fault current limiter(SFCL), a superconducting cable, and a superconducting accelerator with high voltage or high ramping-up rate condition. The electrical degradation characteristics of HTS conductors due to electrical breakdown should be taken into consideration because high electric field intensity induced by high operating voltage or rapid ramping-up rate can affect the dielectric stability. In this study, the electrical degradation characteristics of 2G HTS conductors with different metal stabilizers made by SuNAM Co., Ltd. are analyzed and compared through dielectric experiments. As results, the most appropriate type of a 2G HTS conductor is recommended to manufacture superconducting apparatuses with a high voltage or rapid ramping-up rate condition.

Thrust estimation for HTS-magnet based Magneto Plasma Dynamic Thrusters (MPDT)

At present time, electric propulsion is being considered for outer deep space missions. Magneto Plasma Dynamic Thrusters are capable of accelerating semi- neutral plasma gas (Xenon, Iodine, Argon, Ammonia, or Lithium) to a high exhaust velocity using combination of RF power & high magnetic fields. High Temperature Superconducting (HTS) coils can generate high magnetic field due to high operating current density at temperatures below its critical temperature(Tc). These superconducting coils can be cooled by using the cold of outer dark space. The use of 2nd Generation (2G) HTS coils can increase thrust, by increasing high magnetic field with very low power consumption. Thus, specific impulse due to the combination of RF plasma and HTS based superconducting high magnetic field is increased drastically. In this paper, the thrust calculation are carried out for MPDT for varying magnetic fields produced by superconducting coils. The estimation of exhaust velocity and thrust generated by plasma for an MPDT is of great challenge and is required to determine for calculating the life of mission as well as the distance of travel. These estimations are required to support the indigenous development of MPDT.

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.

절연파괴에 따른 2세대 고온 초전도선재의 열화특성에 관한 연구

2G high temperature superconducting (HTS) wires have been widely adopted to develop high voltage superconducting apparatuses such as a superconducting fault current limiter (SFCL), a superconducting cable, a superconducting transformer, and so on. A study on the dielectric degradation characteristics of 2G HTS wires due to electrical breakdown should be performed to enhance the stability and to accelerate the commercialization of high voltage superconducting apparatuses. In this study, the degradation characteristics of 2G HTS wires, SCN-04 made by SuNAM Co., Ltd. are analyzed by dielectric experiments with AC and lightning impulse voltage in saturated liquid nitrogen (LN2) of 77K. The 2G HTS wire used in this study has silver stabilizing layers on both sides of GdBCO layer. Also, the substrate is made with stainless steel and whole 2G HTS wire is surrounded by copper. It is verified that the degree of degradation of the 2G HTS wire is affected by the magnitude of the applied voltage and the type of voltage. Also, cracked GdBCO layer due to electrical breakdown is shown by scanning electron microscope (SEM) image. The degradation characteristics such as critical current and index n of 2G HTS wire due to electrical breakdown can be explained by mechanical cracked structure of a GdBCO layer.

Temperature-field-angle dependent critical current estimation of commercial second generation high temperature superconducting conductor using double hidden layer Bayesian regularized neural network

We estimated the critical current of the second generation (2G) high-temperature superconducting (HTS) conductor using neural network fitting methods. The critical current of 2G HTS conductors depends on magnetic field strength and angle as well as on temperature, Ic(T, B, θ). Moreover, the critical current values vary for 2G HTS conductors from different manufacturers. In this study, we addressed three challenging issues in critical current assessment by neural network fitting methods, namely 90° asymmetry, a wide range of temperature-field-angle dependence, and different manufacturer conductor differences. Prediction models for three commercial HTS conductors were trained and evaluated by convergence, accuracy, and robustness. The linear regression correlation coefficient R was approximately equal to 1 for the three models. The critical current estimation obtained from the proposed method was compared with the critical current estimation from the interpolation method at different fixed temperatures using a multi-width no-insulation magnet. The model computation speed was also discussed. The proposed model needed only 2.7 s to compute 10 million data sets. Therefore, the convergence, accuracy, reliability, and speed of the proposed method prove that it can be used in a wide range of industrial applications and academic fields.

Intrinsic Influence of Dynamic Resistance on Current Distribution of Two HTS Parallel Branches Without Terminal Contact Resistance

If a superconductor carries DC transport current and exposes to an alternating current (AC) magnetic field whose amplitude is more than its threshold field, a DC resistance so called dynamic resistance occurs on the superconductor because of the dissipative interaction between the DC transport current and the external magnetic field, which possibly appears in many kinds of high temperature superconductor (HTS) apparatus, such as linear synchronous motors. Occurrence of the dynamic resistance significantly affects the current distribution of the HTS components connected in parallel such as cables and conductors except for increasing the AC loses. In this paper, we employ a partially slit second-generation (2G) HTS tape with two branches to study the influence of dynamic resistance on current distribution such that the terminal contact resistances can be avoided. In experiment, DC transport current is applied to the whole 2G HTS tape and branch 1# is only exposed to an applied AC magnetic field. In addition, we use an analytical formulation of the dynamic resistance of branch 1# based on Bean critical state model and voltage calculation of branch 2# relies on E-I curve to build analytical model by using Newton Iteration. It is shown that DC current value of branch 1# decreases and branch 2# increases with the increasing of the dynamic resistance of branch 1#. The results are important for HTS DC devices with carrying ripple current or exposed to AC magnetic field.