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For extra-high-voltage high-temperature superconducting (HTS) cables, not only high electrical insulation performance but also low dielectric loss is required. Therefore, we focus on a porous synthetic paper with lower dielectric loss, e.g., Tyvek polyethylene nonwoven fabric, than that of polypropylene laminated paper (PPLP), which has been used for a conventional HTS cable insulation system. In this paper, we compare partial discharge inception characteristics for different liquid nitrogen/synthetic paper composite insulation systems. The partial discharge inception electric field strength in the composite insulation system depends on the electric field strength in the porous area of synthetic paper. [ABSTRACT FROM AUTHOR]

It is crucial for the successful application of high-temperature superconducting (HTS) power transformers that they are able to survive under abnormal operations, such as a short-circuit fault. Modeling, based on the design of a four-winding three-phase HTS power transformer, suggests severe boiling will occur on the surface of the winding during a short-circuit fault and will jeopardize the turn-to-turn insulation of the HTS power transformer. In this paper, a turn-to-turn insulation breakdown experiment platform involving the introduction of boiling on the surface of electrode has been built. Nomex 410 paper, one of the candidates for turn-to-turn insulation in the design of the HTS power transformer, was tested. The characteristics of dielectric strength of Nomex 410 in three different thicknesses (0.13, 0.18, and 0.25 mm) have been investigated, without boiling, as well as under different boiling situations, in an open bath of liquid nitrogen. The voltage application methods applied during both experiments test the electrical breakdown of Nomex 410 under a dynamic situation. The experiment results show that when under film boiling, compared to the test results for nucleate boiling, the dielectric strength of Nomex 410 paper decreases by approximately 38% of the value when no boiling is involved. Moreover, it is verified that the presence of an electric field accelerates the heat transfer between the liquid nitrogen and the heated electrode. [ABSTRACT FROM PUBLISHER]

This paper proposes a way to represent the anisotropic nonlinear superconducting properties using a discrete model for magnetization with the corresponding critical parameters, equivalent to the Power Law model for currents. This simplified model makes it possible to analyze magnetic systems with superconducting elements in a stationary mode, which reduces the calculation time. Using of proposed model is demonstrated by the calculation of force interactions between high-temperature superconducting (HTS) samples and permanent magnet in zero-field-cooling (ZFC) and field-cooling (FC) modes. HTS bulks in the form of a prism and stack made of HTS tape are considered. The calculation of the electromagnetic field was carried out using the method of integral equations for field sources. The data of calculations are compared with the results of experimental studies. [ABSTRACT FROM AUTHOR]

Corrections to “The Dielectric Strength of Nomex 410 Paper in Liquid Nitrogen under Boiling Situations” [ABSTRACT FROM AUTHOR]

This paper focuses on the current distribution and AC loss of BSCCO/REBCO hybrid tapes. Based on their geometry and E-J character of superconductors, a one-dimensional model is established to compute the current distribution and AC loss under an AC operating current in self-magnetic field. The current distributions of hybrid tapes with different number of REBCO tapes and one BSCCO tape are studied. The numerical and experimental results are in good agreement. According to the current distribution characteristics, AC loss of each tape in the hybrid tape is analyzed and calculated. AC losses of 3 kinds of hybrid tapes are measured and discussed. The method proposed in this paper for AC loss simulation is quite effective for hybrid tapes composited by two or more types of superconducting tapes. [ABSTRACT FROM AUTHOR]

The main obstacle for the application of the high-temperature superconducting (HTS) coated conductors (CCs) in AC energy applications is the relatively large AC loss. To tackle this, several forms of HTS cables for AC applications have been invented and investigated, such as the HTS Roebel cable, Cable on Round Conductor (CORC), and Twisted Stacked Tape Cable (TSTC). In this paper, the possibility of encapsulating Roebel cables into a single HTS CC is investigated, from which a novel conception of a Roebel tape is proposed. Compared with the existing HTS cables, HTS Roebel tapes are more compact, more capable at carrying large current with minimised AC losses, and easier to manufacture. A 3D finite element method (FEM) model of the Roebel tape is built to optimise the structure and verify the performance. The results show that, compared with normal ReBCO CCs, Roebel tapes with optimum patterns can reduce AC transport losses by 60% through field-cancelling and can reduce magnetisation losses by the factor of the filament number through patterning. With excellent loss reduction performance and high current capability, the Roebel tape shows great potential to become a revolutionary HTS cable for high-current power transmission and AC machine applications. [ABSTRACT FROM AUTHOR]

The development of high-temperature superconducting (HTS) electrical machines results in applications of various fields, as they have higher efficiency and power density. Numerical modeling of superconducting electrical machines is usually performed by finite element method based their electrical behavior, and H-Formulation of the Maxwell's equations is one of the models that are used tremendously due to its high flexibility and simplicity. Axial field machine (AFM) is a machine topology with higher efficiency and power density, but with more complexity when modeling. This paper proposed a new 2D model for the superconducting AFM, where the superconducting coil is simulated with a 2D infinitely long model, this model also divides the electrical machine into two parts: the superconducting parts (HTS coils, bulks, etc.) and non-superconducting parts (e.g., conventional conductors, machine structure). This paper compares the results of H-A Formulation and T-A Formulation with this approach, which requires appropriate boundary conditions and continuity between the two regions, along with correct modeling of fixed and moving parts of the electrical machine, where the geometry of this model is based on a linear synchronous machine, which means the rotor is moving linearly instead of rotation. [ABSTRACT FROM AUTHOR]

The Conductor on Rounded Core (${\mathrm CORC}$) cables manufactured by Advanced Conductor Technologies with current densities beyond 300 Amm $^{-2}$ at 4.2 K, and bending diameter of up to 3.5 cm, are considered as one of the strongest candidates for the next generation of high field power applications and magnets. In this paper, we present a full 3D FEM model for their monolayer and bilayer ${\mathrm CORC}$ cables made with up to three and six superconducting tapes respectively, disclosing the full curve of AC losses for the monolayer cable at magnetic fields beyond 60 mT, and the actual distribution of current density along and across the thickness of the superconducting tapes in both designs. The model is based on the so-called H-formulation, allowing to incorporate the true three-dimensionality of the tapes without recurring to 2D thin-film approaches where non-physical surface currents that do not follow the celebrated Bean’s model for type-II superconductors appear. Likewise, good agreement with the experimentally measured AC-losses for the monolayer and bilayer cable have been obtained, with all the details of the model disclosed in this paper. [ABSTRACT FROM AUTHOR]

In the present paper, the possibility of magnetization of HTSC tape by means of pumping by a local magnetic field is considered. Within the framework of the critical state model, the calculation of the density of the induced currents and the magnetization of a square (12 × 12 mm) fragment of a second-generation HTS tape (YBCO) was made. The model considers real dependence of the critical current density on the magnetic field and has been successfully tested previously. In the sample, the currents were induced by the impact of a local magnetic field. The size of the localized area of the external magnetic field to be considered was much smaller than the size of the HTS sample. It is showed that the repeated cyclical impact of the local outer field leads to the accumulation of the total magnetic moment in the sample up to a magnitude of 94% of the theoretical magnetization limit for this sample. The results obtained make it possible to optimize the mode of magnetization of a square fragment of a tape (or a stack of tapes) when implementing a magnetic flux pump. The experimental studies showed results comprisable well with theoretical ones. [ABSTRACT FROM AUTHOR]

With its great advantage in weight and volume, superconducting transformer is considered as potential candidate for the portable power station. To achieve a more compact design, the insulation properties of liquid nitrogen in real operation state is crucial. This paper firstly presents an AC withstand voltage test of liquid nitrogen under different kinds of electric field. Then the bubble influence on the macroscopic insulation performance of liquid nitrogen is analyzed based on finite element method. In addition, the effect of Sumoto effect at liquid surface is also studied by experiments. The results of this paper can be used in future design of compact superconducting transformers. [ABSTRACT FROM AUTHOR]

This is a follow-up study of the cryogen-free superconducting prototype generator with YBCO field windings. The previous paper had introduced the design of the structure, cryogenic system and electromagnetic characteristics of the prototype machine, whose operating temperature was 30 K, maximum field current was 100 A and rotating speed was from 10 to 30 rpm. In this paper, the optimization of the airgap magnetic field and the stability of superconducting magnet have been carried out. For the purpose of increasing utilization of the magnetic field of superconducting windings, its support structure and vacuum chamber of the cryostat had been upgraded in order to reduce the physical airgap between the armature teeth and the vacuum chamber room temperature wall from 10 mm to 2 mm. In addition, a new coil curing method, vacuum impregnation process with paraffin, had been applied while the YBCO coil fabrication, to improve its stability. The performance properties of the optimized system as well as the comparison between FEM simulation and experimental results are finally presented. [ABSTRACT FROM AUTHOR]

High temperature superconductors have zero resistance under critical temperature and the HTS tapes have low thermal conductivity. The China Fusion Engineering Test Reactor(CFETR) project requires current leads with current carrying capacity up to 100 kA, making high temperature superconducting current leads the ideal choice. The main work of this paper is the theoretical analysis and optimization design of the 100 kA HTS current lead. Current leads are designed to minimize heat leakage to the cryogenic system and to reduce the mass flow of cooling gas. In this paper, some important design parameters are introduced firstly, and then one dimensional thermal analysis is carried out for the heat exchanger and high temperature superconductor parts. The LOFA time and overheating time of the current lead were calculated through simulation, and it was verified that the design meets the requirements of the project. Finally, the factors that have great influence on the performance of current leads are analyzed. In view of the four influencing factors, which are joint resistance, GHe inlet temperature, hPw and RRR, we respectively produced an optimized design. [ABSTRACT FROM AUTHOR]

Angular dependence of second generation (2G) high-temperature superconducting (HTS) tape is a crucial parameter for its industrial applications. Known as soldered-stacked-square (3S) HTS wire, a novel structure of HTS wire has been proposed in our previous research. In this paper, angular dependence of 1 mm HTS tape, 4 mm tape, 1 mm 3S HTS wire, and 1 mm 3S HTS twisted wire were measured in liquid nitrogen bath, respectively. It can be found that the 3S HTS wire would not enhance the critical current density under external magnetic field, while an isotropic angular dependence is obtained when 3S HTS wire is twisted. The test results obtained in this paper provides useful information for the future applications of 3S HTS wire. [ABSTRACT FROM AUTHOR]

In this paper, we describe a cooling system for a high temperature superconducting (HTS) magnet of 10 MW class superconducting wind power generator (SWPG). To cool the HTS magnet below 35 K, a novel neon-helium hybrid cooling system is proposed. Neon cools the heat exchanger based on the thermosiphon principle and a cryogenic blower forcibly circulates helium gas between the heat exchanger, attached to a rotating neon vessel, and the HTS magnets. This cooling system has two advantages: applicability to large rotating HTS magnets and high reliability by removing a cryogenic or a high-pressure rotating coupling. To verify the performance of this cooling system, a lab-scale performance evaluation system(PES) is designed. The PES will be proved by cooling the generated heat and penetrated heat of the HTS magnets during operation. This paper describes the detail design process and the preliminary test results of the fabricated cooling system. [ABSTRACT FROM AUTHOR]

Maglev technologies have been extensively studied for modern transport systems; however, their main applications are limited to transportation systems with fixed tracks. On-road vehicles could have a broader outlook if combined with maglev technologies, for which electrodynamic wheels (EDWs) have provided a possible solution. Conventional EDWs are designed based on permanent magnets (PMs), which generate limited thrust and lift forces while having a low power density. In order to enhance the feasibility of EDWs in maglev vehicles, a novel design of EDWs based on high-temperature superconducting (HTS) Halbach array magnets (HAMs) has been proposed in this paper. The suggested design is made of the second generation (2G) superconducting coils, which have been modeled with the A-formulation and T-formulation based finite element methods. Simulation results show that the proposed HTS HAM EDW can generate higher thrust and lift forces, improve the magnetic flux density distribution in the airgap, and greatly reduce the weight of the magnets compared with the conventional design. This paper provides a possibility for future on-road maglev vehicles. [ABSTRACT FROM AUTHOR]

High critical current density is desired for cables adopted in fusion or accelerator applications. The bending diameter of REBCO tapes is very important for the preparation of such cables. The bending diameter of REBCO tape is related to many factors. It is necessary to identify the most important factors determining the bending diameter by experiments. In this article, a new measurement method for bending diameter is developed. Short samples are taken from individual tapes in a large batch and connected in series into one long piece for bending diameter measurement. This way, a large batch of tapes can be efficiently assessed in one go. The samples prepared by Shanghai Superconducting Technology Co., Ltd. (SST) have been tested. It is concluded that the critical bending diameter of the tapes, which we define that the critical current attenuation is less than 10%, is closely related to its thickness, stiffness, superconducting layer thickness, and copper plating thickness. The composition of the superconducting layer has little effect on it. By testing the tapes prepared by SST in large quantity, it is found that when the REBCO faces inward during bending, tapes plated with 5 and 10 μm copper on one side only have smaller critical bending diameter than tapes plated with copper on both sides. The current has no attenuation when the bending diameter is 2.6 mm. When REBCO faces outward, copper plating has little effect on the critical bending diameter, which varies between 6 and 14 mm. [ABSTRACT FROM AUTHOR]

High temperature superconducting generators (HTSGs) have great potential of high power density for future large direct-drive wind turbines. As synchronous machines, HTSGs have rapid rise of field currents during a sudden short circuit fault which cause AC losses in the HTS tapes. This paper applies H-A formulation of Maxwell equations for finite element simulation of electromagnetic behavior of a 10 MW, 9.6 rpm HTSGs. The model is integrated to a short circuit model to calculate the characteristics of the HTS field winding, such as field currents and AC losses during a three-phase no-load short circuit fault at the armature winding terminal. Two HTSG designs are compared. The $n$ value characterizing the sharpness of the superconducting-resistive state transition of the HTS tape and the number of armature winding segments are analyzed as key variables. The result indicates high AC losses are produced but more armature winding segments can effectively reduce the AC loss and the field current. A lower $n$ value can also lower the AC loss level but only for the non-magnetic rotor design. The field current is not affected by the $n$ value for both HTSG designs. [ABSTRACT FROM AUTHOR]

This article presents an integral modeling approach for computing ac losses in high-temperature superconductors near magnetic materials. The current density and magnetic field distributions are calculated by solving Maxwell's equations in integral form in the active parts. Equivalent surface and interface current densities are considered in the magnetic material to take into account its magnetic field-dependent relative permeability. The proposed approach is applied to compute ac losses in a second-generation high-temperature superconducting tape with a magnetic substrate. The obtained results are compared with the finite element method using H formulation to check the validity and performances of the proposed integral approach. [ABSTRACT FROM AUTHOR]

Spoke structure can increase the torque density of coaxial magnetic gear (CMG). However, the outer rotor can produce a large number of magnetic leakages. To improve the utility of PMs, a novel magnetic gear was proposed in this paper. The structure of the auxiliary flux modulator is a slotted iron yoke, and the slot angle is same as the stationary ring. Among, the permanent magnets (PMs) of inner rotor are adopted uneven block structure to improve air gap flux density. At the same time, the stationary ring adopts high-temperature superconducting (HTS) bulks, replacing the epoxy resin. In addition, Genetic algorithm (GA) is applied to calculate the optimal parameters of the proposed CMG. Finally, the air gap flux density and output torque of the magnetic gear a compared by the finite element method. The results show that the output torque of the proposed magnetic gear is effectively improved. [ABSTRACT FROM AUTHOR]

The performance of High Temperature Superconducting (HTS) tapes is strongly affected by the mechanical loadings they experience during manufacturing, cooldown and operation. Therefore, the development of HTS-based applications requires thorough investigations on the impact of these loadings on the critical current. In this work, a measurement procedure is applied to determine the critical current of a (Re)BCO tape at 77 K, after double bending at room temperature around a cylindrical mandrel. In this procedure, the tape is cooled down to cryogenic temperature, and the critical current is first measured on the straight sample. After warming the tape up to room temperature, a double bending around a cylindrical mandrel is applied in two opposite directions and the critical current is measured at the following cooldown. This analysis is repeated for different mandrel diameters in order to identify to study the impact of the curvature radius on the performance degradation. The application of one single bending at room temperature is compared to the results of the double bending procedure. The influence on the performance degradation of applying a known force to the tape during the double bending at room temperature is also experimentally analyzed. [ABSTRACT FROM AUTHOR]

Stress calculation is a key link in evaluating whether the structure of a superconducting magnet is safe. A 35-kV/3.5-MVA single-phase high temperature superconductivity-controllable reactor (HTS-CR) with the HTS winding wound by HTS double pancakes is being developed. The effect on the local stress and temperature rise of HTS double pancakes, which determines the design of the strengthening structure of the HTS double pancake, is studied in this paper. Furthermore, the multiprocess stress development for HTS double pancakes from manufacturing to power-on is also investigated, which discloses the model and the results of the stress calculation. This study can provide a reference for developing HTS-CR with large capacity in the future. [ABSTRACT FROM AUTHOR]

Second-generation high-temperature superconducting (HTS) tapes strongly rely on the substrate material, in many cases Hastelloy C276 (“H-C276”). In order to ameliorate performance (and reduce the price) of superconducting tapes, replacement of H-C276 has been investigated. In this paper, the potential of the readily available austenitic stainless steels X2CrNiMo17-12-2 (“CrNiMo”) and X11CrNiMnN19-8-6 (“CrNiMnN”) as substrates is assessed. It was found that CrNiMnN is not suitable as a replacement for H-C276. Tensile stresses occurring at elevated temperatures during the HTS tape production result in plastic deformation of the CrNiMnN substrate. In the case of CrNiMo, however, plastic deformation was not observed after processing of the HTS tape. Electrical losses as a result of alternating currents beyond those of H-C276 did not occur due to the paramagnetic nature of CrNiMo. It is demonstrated that, for the very same processing parameters, HTS films deposited on electrochemically polished and buffered CrNiMo substrates exhibit similarly high critical current densities as on polished and buffered H-C276 substrates. The application of CrNiMo stainless steel reduces substrate costs considerably. More importantly, tapes processed on CrNiMo substrates withstand higher tension strains with respect to the reduction of the critical current compared to H-C276 substrates. This effect is interpreted to be a result of the matching coefficients of thermal expansion of the HTS layer and CrNiMo, resulting in lower residual tensile stress in the HTS layer after processing. [ABSTRACT FROM AUTHOR]

Magnetization loss is an important parameter in the design of high-temperature superconducting (HTS) power devices. It is produced under the external alternating magnetic fields. In previous work, for the purpose of reducing the loss, our group proposed and fabricated a novel soldered-stacked-square (3S) HTS wire with a cross-section of 1 mm × 1 mm. In this paper, the magnetization losses of the 3S wire are investigated numerically. First, numerical and theoretical losses in single HTS tapes are compared and their consistence proves the reliability of the numerical model. Also, the losses in tapes of different widths are evaluated, which shows the 1-mm tapes have less magnetization losses under perpendicular field. Moreover, the numerical model for estimating losses in 3S wires has also been built. According to a series of calculation and comparison, the 1-mm stacked wires have less losses than those wider stacked wires under perpendicular field. Besides, considering the practical application of HTS power devices, angular dependence of the loss in 3S wires containing one HTS tape is studied as well. The results indicate the loss increases with the increase of the angle with respect to the wire surface. [ABSTRACT FROM AUTHOR]

This paper studies the current limiting behavior based on an air-core high-temperature superconducting transformer (HTST) and a group of inductor–capacitor series resonant limiters. The air-core HTST is composed of four same double-pancake type high-temperature superconducting coils made up of Bi-2333/Ag tape, and both of primary and secondary windings include two series superconducting coils. It plays the roles of inductive fault current limiting and transformation impedance; in addition, the magnetic flux saturation can also be avoided. Meanwhile, the inductor and capacitor series with the secondary winding of the air-core HTST in series resonance state are the conventional devices. The influence of them on the circuit can almost be ignored, because they are in series resonant state in normal operation. While the fault current appeared in the primary circuit, it will be limited by the impedance of the air-core HTST and the inductor without quench (the inductor and capacitor would quit the series resonant state). According to the preliminary experiment carried out in our laboratory, this superconducting current limiting module can operate as expected, and its behavior is satisfactory. [ABSTRACT FROM AUTHOR]

The electrical breakdown strength of insulation material is very important for the design of a high-temperature superconducting (HTS) cable. This article investigates the breakdown characteristics of polypropylene laminated paper (PPLP) film samples, which are widely used in an HTS cable. Various test conditions, such as different modes of increasing voltage, voltage types, and ambient temperatures, are used. It is found that the breakdown strength of the PPLP film samples varies greatly with the aforementioned experimental conditions. Based on the existing research, the key reasons for the experimental phenomenon are analyzed. The experimental results provide the reference experimental data for the insulation design of the HTS cable. [ABSTRACT FROM AUTHOR]

When a high temperature superconductor (HTS) coated conductor carries a DC transport current within the background of an oscillating magnetic field, the effect of dynamic resistance takes place. Under the circumstance when the dynamic resistance effect is significant, heat dissipation will be generated to change the temperature of HTS tapes. The amplitude of the instantaneous dynamic resistance increases with time due to the rising temperature. The phenomenon is more obvious when it comes to the HTS stacks where superconducting tapes are assembled so close. This paper proposes a numerical model with electromagnetic and thermal coupling to study the dynamic resistance of the series-connected HTS stack. Experimental results have shown that the proposed numerical model can describe dynamic resistance more accurately than conventional models. Besides, investigations are carried out on how the insulation thickness in the stack and the frequency of AC magnetic fields impact the dynamic resistance of HTS stacks under the influence of Joule heat. This can provide a useful reference for the design of superconducting devices in which dynamic resistance occurs. [ABSTRACT FROM AUTHOR]

The realization and preliminary tests of a high temperature superconducting axial-field synchronous machine (HTS-AFSM) prototype are presented in this paper. The HTS machine consists of a 3-phase stator with HTS armature winding and a permanent magnet (PM) rotor. The HTS armature winding contains three pancake coils made of BSCCO tape forming a single layer nonoverlapping concentrated stator windings. The rotor is composed of four NdFeB permanent magnets. Several tests have been carried out such as voltage vs. currents curves of the HTS coils, static torque, back-EMF and load tests in generator mode. A 3D semi-analytical model, based on integral equations, has been used to check out the measured electromagnetic quantities. It has been shown that the measured and the calculated quantities are in satisfactory agreement. [ABSTRACT FROM AUTHOR]

Quench has always been an urgent problem for high temperature superconductor (HTS) magnets. Fast discharge of the coil current is an effective method to protect the HTS magnet from quenching. In HTS magnets, metal plates are originally used to provide conduction cooling and mechanical support for the coil. During fast discharging operations, the metal plates can rapidly absorb part of the magnetic energy stored in the HTS coils through electromagnetic coupling. Previous studies are based on copper plates. This paper studies the influence of several promising metal materials on the discharging process of the HTS coils coupled with metal plates by experiments and simulations. The results show that in the explored resistance range, the higher the electrical conductivity of the metal plates, the better the acceleration of the current attenuation of coil at the early stage of discharging process. The effects of different metal plates on accelerating current attenuation of the coil are ranked as follows: SS 304L < Al 6061-T6 < Al (RRR = 30) < Cu (RRR = 30) < Au < Cu (RRR = 300) < Ag. However, Cu (RRR = 300) plates can absorb more energy from the HTS coil than the Ag plates during the discharging process. Copper with higher purity (Cu (RRR = 300)) and silver are promising alternatives for metal plates of HTS magnets. Generally, a fast current drop is always the most effective method for avoiding tape turn-out during a local quench; therefore, silver with the highest electrical conductivity is the best choice in view of quench protection. [ABSTRACT FROM AUTHOR]

In this work, we experimentally investigate the current carrying capacity of single REBCO tapes and stacks made 5 12 mm REBCO tapes with a 25 μm copper stabilizer in liquid helium in comparison with those made of bare tapes with no stabilizer at current ramp rates up to 55 kA/s. The motivation for the research was checking the usability of REBCO stacks as basic sub-elements for high current superconducting cables operating in fast cycling modes at 4.2 K. An original experimental technique was employed to induce the extremely high ramp rates. During the tests, one or 5-folded stacks curled into rings 95 mm dia with different types of joints were charged in the external magnetic field generated by an outer solenoid at ramp rates up to 1.6 T/s. The curled REBCO stacks were either soft-soldered over their entire length or contained local joints only. The maximum screening current induced in the samples during the outer solenoid charging Imax was registered. Our experiments showed that the current carrying capacity of the REBCO tapes and stacks was strongly affected by the absence or presence of the copper stabilizer as well as the type of the joint. The reasons for the Imax limitation for the copper stabilized and bare samples are also briefly discussed. [ABSTRACT FROM AUTHOR]

Since the 1970’s the effect of the increase of the critical current of superconductors in the longitudinal external magnetic field has been known. The critical current density of a Nb-Ti wire at low longitudinal magnetic fields demonstrated several times the larger value compared with that in a transverse magnetic field. The same phenomenon has been observed for 2G HTS tapes. It is natural to try to use this phenomenon to increase the critical current in DC HTS power cables. In this paper, we present the analysis of feasibility to use the longitudinal magnetic field effect to increase critical currents in practical HTS power cables. The experimental model of the HTS DC cable has been developed, produced, and tested in liquid nitrogen. The increase of the critical current observed when the longitudinal magnetic field generated. This increase coincides with the calculations. [ABSTRACT FROM AUTHOR]

This paper reported the fabrication and the test results of the high temperature superconducting (HTS) magnet developed for the aluminum billet heater for aluminum extrusion processing. In this magnet, the HTS coils were combined with iron cores, because the required magnetic field in the working region was about 1T. Two HTS coils wound directly on the convex shape iron cores were fabricated. The HTS coils were made by the no-insulation winding of REBCO tape with the YOROI-coil technique. Each of them was separately installed in an individual cryostat. Two HTS coils with iron cores were disposed oppositely to each other and were magnetically connected by a C-shape yoke placed in room temperature. The HTS coil was cooled down to about 15 K by the GM cryocooler in the initial cooling. The magnetic field of 1.06 T at the center of the heating region was stably generated with the rated current of 200 A. It was also demonstrated that the HTS magnet could be charged up to 300 A without quench. According to the observation of the electromagnetic force direction from the outside of the cryostat, it was confirmed the validity of the force balance design of the magnet. [ABSTRACT FROM AUTHOR]

In recent years, the increase of microplastics (MPs) in ocean have been recognized as one of ocean pollution listed in Sustainable Development Goals (SDGs). Since MPs absorb harmful chemicals while floating in ocean, small fish which eats the absorbed MPs may fall into bad digestion and poor health condition. To solve the ocean pollution problem, a good MP collection method must be proposed with a high processing speed and a high MP collection ability. While, recently, the performances of 2nd generation high-temperature superconducting (HTS) magnets which can generate a field higher than 15 T have been improved. It is expected that MP collection performances are enhanced with such high field superconducting magnets. In this paper, we propose a conceptual design for MP collector from seawater using superconducting magnets. To evaluate the performances of the device, we developed a fluid simulation coupled with magnetic field simulation. The simulation results indicate that MPs can effectively be collected with a high magnetic field with a high processing speed. [ABSTRACT FROM AUTHOR]

The performance of High Temperature Superconducting (HTS) tapes is strongly affected by the mechanical loadings they experience during manufacturing, cooldown and operation. Therefore, the development of HTS-based applications requires thorough investigations on the impact of these loadings on the critical current. In this work, a measurement procedure is applied to determine the critical current of a (Re)BCO tape at 77 K, after double bending at room temperature around a cylindrical mandrel. In this procedure, the tape is cooled down to cryogenic temperature, and the critical current is first measured on the straight sample. After warming the tape up to room temperature, a double bending around a cylindrical mandrel is applied in two opposite directions and the critical current is measured at the following cooldown. This analysis is repeated for different mandrel diameters in order to identify to study the impact of the curvature radius on the performance degradation. The application of one single bending at room temperature is compared to the results of the double bending procedure. The influence on the performance degradation of applying a known force to the tape during the double bending at room temperature is also experimentally analyzed. [ABSTRACT FROM AUTHOR]

The appealing advantages of high-temperature superconducting (HTS) power transformers over conventional ones have attracted transformer manufacturing companies, power companies, research institutes, and universities worldwide to conduct research and development in this field. Unfortunately, HTS transformers are more vulnerable to mechanical stresses than conventional transformers. The results of the interaction between current carrying windings and leakage magnetic fluxes are the electromagnetic forces, which act on transformer windings. Under short circuit events, these forces are remarkable, and, therefore, catastrophic failure of transformer may arise. Flux-diverter applications have been reported in earlier literatures for increasing critical current or decreasing ac losses in HTS transformers. In this paper, a genetic algorithm based method is employed for the optimal design of flux diverter to minimize the axial short circuit force, in design stage of a sample 132/13.8 kV, 50 MVA three-phase core type HTS transformer. In this paper, the optimal dimensions, placement, and permeability of a flux diverter have been determined. It has been shown that utilizing this optimized flux diverter, the axial short circuit forces have been reduced significantly. Electromagnetic modeling and simulations, by the application of finite element method, have been employed for the verification of the analytical method results. A high degree of consistency has been observed between the analytical results and the simulation results. [ABSTRACT FROM AUTHOR]

Due to the nonlinear properties of superconductors, modeling of high-temperature superconducting (HTS) devices is difficult, especially for the ones in large scale. In this paper, we develop the multiscale model from a two-dimensional (2-D) planar geometry to a 2-D axisymmetric geometry to successfully calculate ac loss of large-scale HTS coils. By applying appropriate boundary conditions, the infinite-turn coil is built in the 2-D-axisymmetric model to produce approximated current density for an HTS coil. Besides, the multiscale model is improved in terms of coupling, so that submodels can be connected in one file and the external data processing is not needed. Validation on accuracy and efficiency is demonstrated through a double-pancake coil. Results are compared with a conventional model that considers the superconducting characteristics on each turn of the coil in actual size. This paper shows the development and improvement of multiscale model in the 2-D axisymmetric geometry is feasible. Due to its high accuracy and efficiency, the developed multiscale model can be a useful approach to analyze electromagnetic characteristics and calculate ac losses in large-scale HTS magnets. [ABSTRACT FROM AUTHOR]

To enhance the operating security and stability of the cross-linked polyethylene power cable based urban distribution network due to conventional cable joint (CCJ) faults, this paper presents a novel superconducting fault current limitation scheme by using a superconducting cable joint (SCJ). The basic principle, circuit modeling, conceptual design and distribution network integrated with the SCJ are presented in detail. The comparative study without and with the proposed SCJ scheme and comprehensive evaluation are carried out. The simulation results obtained under symmetrical and asymmetrical CCJ faults show that the harmful large fault grid currents can be limited effectively and the fault grid voltage can be well improved. Thus the high temperature electric arc in the fault location caused by CCJ faults can be safely controlled. And large area power failure in actual power system can be avoided. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) no-insulation (NI) magnet excited by rotating flux pump has the characteristics of high current density, high field stability and small volume, which is in accordance with the development trend of MRI/NMR equipment for main magnet. In poor electromagnetic environment, however, quench detection of direct electrometric method based on threshold judgment is easily interfered by noise and severely disrupted quench signal may cause wrong quench determination and malfunction of quench protection, thereby resulting in unnecessary loss. To suppress the influence of the noises caused by current fluctuation and the rotation of motor on the correction of quench determination or accurate reading of data. Therefore, this paper compares and analyzes the experimental and filtering data detected by equipment based on wavelet de-noising algorithm, and verifies the necessity of using wavelet filtering data. [ABSTRACT FROM AUTHOR]

Once the miniaturization of high-performance magnetic resonance imaging (MRI) scanner was accomplished, extremely stringent indexes were needed for the magnetic field, the operational stability and mechanical strength. We adopted “No-insulation (NI) winding technology” to build high-temperature superconducting (HTS) magnets for 3-T grade MRI, in order to achieve these stringent indexes. To realize a compact size of 3-T MRI, the electromagnetic stress of HTS magnet becomes a technical challenge. In this paper, we investigated the construction of an electromagnetic stress reinforced structure for HTS magnets of 3-T MRI. First, the electromagnetic force was estimated, and the distributions of stress and strain induced by electromagnetic force in the winding part of the HTS magnet were reproduced using a finite element analysis. Meanwhile, the influences of the interlayers between sub-coils, shells and blind flanges on the stress property of HTS magnet were evaluated. Based on these results, the material and its consumed volume established the reinforced structure employed of the HTS magnet were also clarified. Finally, the utility of reinforced structure was verified for NI HTS magnets deployed in 3-T MRI. [ABSTRACT FROM AUTHOR]

For the design of superconducting magnets, the magnetic field and critical current distributions are usually calculated based on finite element software such as COMSOL, ANSYS, etc. These software are necessary for accurate structure modeling and field calculation, but they occupy large memory space and comsume long simulation time. Furthermore, they are not easy to use. To achieve an easy-to-implement solution for rapid magnet field and critical current calculations, this paper investigates three types of analytical calculating methods, and builds an autonomously-operated calculating application program (APP) for the uses in various superconducting magnets. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a variable protective resistor that realizes controllable energy dissipation and temperature inhibition for the no-insulation (NI) HTS coil-systems, during sudden discharging. The resistor is paralleled with the meter-class bore NI coil, which aims to be used in a high-field magnetic resonance imaging scanner (MRI), to avoid burn-out and shorten restart time of the coil when it has to be shut-down during an accident. To establish the relationship between the value of protective resistor, the energy dissipation and the temperature increase during sudden discharging for the NI coil, in this study, a numerical analysis coupled with a partial element equivalent circuit and a thermal analysis was conducted. Based on the results, the mechanism that how a protective resistor shares energy dissipation and inhibits temperature increase, has been clarified. Meanwhile, the effects of the value of protective resistor on the discharging behavior and temperature increase of NI pancake coil during sudden discharging, were also evaluated to verify the feasibility of this protection method in the application of MRI. [ABSTRACT FROM AUTHOR]

A simplified two-dimensional (2D) model, which takes the helical structure of the conductor on round core (CORC) cable into consideration, is utilized to analyze the electromagnetic and thermal properties of the cable. The model couples multi-physical fields through the JcBT(B,T) properties of the superconducting tape. We first introduced the modeling strategy and verified the validity of the 2D model. Then, considering the influence of thermal on the critical current of the tape, the cable loss under different conditions has been calculated. By changing the relative positions of the inner and outer conductor layers of the 2D model, the influence of the magnetic field on CORC cable loss can be obtained, and it can be extended to the periodic three-dimensional (3D) structure. [ABSTRACT FROM AUTHOR]

Based on existing quasi-isotropic strand (QIS) conductor and twisted stacked tape cable–cable in conduit conductor (TSTC-CICC), this paper proposed a novel QIS-CICC. The conductor was numerically modeled and the anisotropy of critical currents was analyzed. The simulations showed that although the critical currents of the QIS-CICC were worse than those of the TSTC-CICC for the self-field condition, the current decay of the QIS-CICC was far less than that of the TSTC-CICC under a 1 T external field, and the anisotropies of the two conductors were almost the same. [ABSTRACT FROM AUTHOR]

Tokamak device requires a very high current power supply from the local power distribution sources to the targeted magnets such as toroidal field (TF) coils and poloidal field (PF) coils. This paper presents a preliminary design of a 30-m/1-kV/10-kA low voltage direct current (LVDC) superconducting cable for the potential in Tokamak applications. The outer diameter of the DC cable is 122.41 mm, and the pressure drop of liquid nitrogen (LN2) in the inner and outer channels is about 6.59 kPa. The flow velocity of inner and outer LN2 channels are 0.5 m/s and 0.25 m/s, respectively. The temperature rise of the entire cable was designed to be less than 5 K, which enhances the electricity supply safety and reliability. These preliminary design lays some technical bases for achieving high current and low loss power transmission. The designing results show that the LVDC superconducting cable has significant potentials for Tokamak applications compared with conventional copper cables. [ABSTRACT FROM AUTHOR]

The Tri-axial high temperature superconducting (HTS) cable usually subjects to the impact of the fault currents in the power system. During the fault, a large amount of the Joule heat is generated, which may be damage cable. In this paper, an analysis model of electromagnetic thermal transient characteristics of the 10 kV/1 kA cable is built. The transient characteristics of the HTS cable are analyzed under a fault current of 15 kA rms lasting 0.14 s, and the current, resistance and temperature of the HTS cable are obtained. The maximum temperature of the HTS cable is 153.1 K under fault current. Meanwhile, the safe operating range of the HTS cable under the fault current of 15 kA to 25 kA is obtained. the analysis results will provide the theoretical basis for the quench protection and relay protection strategy of the tri-axial HTS cable in the Grid. [ABSTRACT FROM AUTHOR]

On the basis of 24 T magnet, the Institute of Plasma Physics, Chinese Academy of Sciences are developing 35 T all superconducting magnet. The magnet was designed as a combination of 20 T REBCO insert coil and a 15 T 150 mm low temperature superconductor background magnet. The 20 T insert coil consists of two coils nested together. NI winding technology is applied to coil 1 to increase its current density. The 50 μm thick Hastelloy tapes will be used to co-wind with REBCO tapes of the coil 2 to further improve its over-all mechanical strength. Electromagnetic analysis shows that the maximum ratio of operating current to the critical current of coil 1 and coil 2 is 0.63 and 0.37 respectively. A more accurate model for calculating strain considering screening current is under study. The inner joint is applied to the coil 1 to avoid in-plane bending of REBCO tape, and the detailed preparation method is given in the paper. The winding and preliminary testing of all double pancakes of coil 1 have been completed, and the winding of coil 2 is in progress. This magnet is planned to be assembled and tested in 2021. [ABSTRACT FROM AUTHOR]

Second-generation high-temperature superconductors, being brittle, need to be deposited on a substrate and converted to tapes with additional reinforcement layers. These tapes are wound on a core to make superconducting wires and cables. The mechanical loads during bending, twisting, winding, etc., can degrade the superconductor. It is necessary to determine the strain-induced during these processes. Variations in induced strain with bending of superconductors have been investigated analytically and numerically for various configurations of Rare-Earth Barium Copper Oxide (REBCO) tape. The numerical simulation has been carried out using COMSOL Multiphysics software; the analytical examination of the effect has been performed applying the Flexure formula. The geometrical configuration of the superconducting tape is varied in terms of the bending radius, the thickness of constituting layers made of Hastelloy and copper. The results showed that the variation in the thickness of the substrate has a large influence on the induced strain. Electrical performance analysis is also carried out using the power law of strain dependence and the 5% critical current degradation point is noted. Results of these numerical and analytical investigations are expected to help in finding out critical parameters to avoid degradation while being in use. [ABSTRACT FROM AUTHOR]

With the demand for data processing and storage increasing rapidly, the existing CMOS-based computing system is gradually unable to meet the amplification demand because of its high-power consumption. Due to high frequency and low power consumption, superconducting rapid single-flux-quantum (RSFQ) logic circuit technology is an attractive candidate. In this paper, we propose a novel placement method based on the layer layout. We layer the gates according to the logic level, which is the length of the longest path in terms of the number of clocked gates from any primary input (PI) of the circuit to the gate. Dummy gates are inserted so that any two adjacent layers can form a bipartite graph. Then the gates of each layer are reordered to minimize the half-perimeter wirelength (HPWL). Finally, the gates of each layer are assigned vertical positions to make the edges as straight as possible. The distance between adjacent layers is determined by the number of bending points of the edges between layers. We use several superconducting RSFQ logic circuits to evaluate the effectiveness of our proposed placement method, which uses HPWL and area as evaluation metrics. The experimental results show that compared with the Simulated Annealing (SA)-based placement method, the proposed approach can reduce the total HPWL and total area by an average of 77.77% and 57.56%, respectively. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to present a minimum volume optimal design method of hybrid magnetic resonance imaging (MRI) magnet using field superposition. The hybrid MRI magnet made by high-temperature superconductor (HTS) and low-temperature superconductor (LTS) is the optimal approach of producing higher magnetic field, which also reduces volume than LTS. In this study, the field superposition theory combined with linear programming and nonlinear optimization is introduced in advance to get minimum volume. Considering the different advantages of LTS magnets and HTS magnets, three hybrid MRI magnet configurations are introduced: (1) HTS insert and LTS outsert: (2) Minimum HTS magnet under LTS magnet: (3) Minimum LTS magnet under HTS magnet. In addition, the homogeneity over the central sphere volume and the scope of 5 Gauss fringe field are considered in actively shielding MRI design. Finally, the three different configurations are compared and a 7 T hybrid actively shielding MRI magnet is presented. The designed magnet homogeneity and 5 Gauss fringe field are validated by finite element simulation method, which illustrates the efficiency and the flexibility of the proposed optimal method. [ABSTRACT FROM AUTHOR]

This paper deals with the possibility of applying superconducting motors and hydrogen fuel cells to electric aviation propulsion systems (APS) for the development of next-generation APS. Instead of the conventional fossil fuel-based power generation system, the APS using hydrogen fuel cells and superconducting motors was conceptually designed. The proposed APS consists of a superconducting motor, a hydrogen fuel cell, a liquid hydrogen tank, and a battery. For specific power comparison, the proposed APS capacity was the same as that of a commercial APS, and the capacity and weight of the hydrogen fuel cell and battery were calculated. The 5 MW superconducting motor was designed and analyzed focusing on magnetic field distribution, thermal load, mechanical stress, efficiency, weight, and specific power. As a result, the proposed APS is expected to reach the level of performance applicable to aircraft in the near future, given the recent development trend of battery and liquid hydrogen technology. These results are expected help in a future-oriented APS design. [ABSTRACT FROM AUTHOR]

The distributed propulsion aircraft with HTS electrical system is a novel concept for future airliners, which can reduce by more than 70% fuel burn and NOx emissions. The circuit breakers ensure the security of this novel aircraft by isolating electrical faults timely. Solid-state circuit breakers (SSCBs) are preferred due to their fast response and high performance in the cryogenic circumstance. However, the high conduction loss of SSCBs impedes their further application. A mechanical switch using liquid nitrogen (LN2) as an arc extinguishing medium shows excellent DC current interruption performance. The LN2 switch is characterized with extremely low contact resistance, and the proper use may reduce the conduction loss of power switches significantly. Nevertheless, the effect of metal type arc chutes on the arcing process in the LN2 is still not clear. Thus the objective of this paper is to understand the effect of metal type arc chutes on the current interruption performance of LN2. Silicon iron arc chutes are employed. Neodymium (NdFeB) magnets are used to stretch the arc into the arc chutes. The maximum interrupting current is 1 kV/ 2 kA when only magnets are applied. Further applying the arc chutes leads to a significant drop in the arc voltage and interruption performance. Since the high relative permeability of silicon iron weakens the magnetic field acting on the arc, metal type arc chutes are not recommended. 1 kV / 10 kA fault current is successfully cleared by the combination of resistance type superconducting fault current limiter (R-SFCL) and LN2 switch with magnets, during which the R-SFCL responds to the fault within 420 μs, compensating the long clear time of the LN2 switch. [ABSTRACT FROM AUTHOR]