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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]

In this paper, seven groups of sheet insulation for use in liquid nitrogen immersed power transformers have been tested under three different standard electrodes from ASTM D149-97a. The seven groups consist of three different types of paper/film, nonadhesive Kapton 100 HN (Kapton), THERNOMID 14.20 paper (NMN), and Nomex 410 paper (Nomex). The porous paper, Nomex 410, is found to have ac dielectric strength of 62–68 kV/mm, which is likely to be independent from its thickness. The nonporous film, Kapton, shows the dielectric strength of 288 kV/mm, whereas NMN paper has a dielectric strength of 74–78 kV/mm, larger than Nomex with similar thickness. Liquid nitrogen gaps near the triple junction of electrodes as well as liquid nitrogen pockets between the fibers are the main sources of partial discharge (PD) for NMN and Nomex. For Kapton, PDs are more likely to occur in the cavities filled with liquid nitrogen, either on the surface of the electrode or around the impurities on the surface of the film. Electrodes with a small stressed volume are more appropriate for dielectric tests of thin paper/film insulation, such as Kapton, due to the lower influence of cavities on the electrode surface. In contrast, electrodes with a large stressed volume and uniform electric field distribution are suitable for the papers such as Nomex and NMN. [ABSTRACT FROM AUTHOR]

Breakdown (BD) and partial discharge (PD) characteristics of insulating paper and transformer board materials are investigated as cost-effective alternatives to high-price materials like polyimide (PI) or polytetrafluoroethylene and fiber reinforced plastic materials typically used in superconducting devices based on high temperature superconductors cooled with liquid nitrogen (LN2). Three different cotton and cellulose based insulating papers are tested in LN2 at atmospheric pressure and compared to synthetic sheet materials and polypropylene laminated paper (PPLP). Additionally, the BD performance and PD characteristics of three different transformer board materials are investigated in LN2 . The results reveal that the paper and board materials have nearly the same or even slightly higher BD voltages in LN2 in comparison to the values in insulating oil. The pure paper materials with thicknesses of 130 μm have a dielectric strength of 70-90 kV/mm, whereas values of 130-140 kV/mm are measured for PPLP and PI with nearly the same thickness. The dielectric strength of the board materials has a maximum value of 76 kV/mm. In the frame of the investigations, the BD performance of the pure paper materials in LN2 is not influenced by the water content of the materials, dried and undried specimens have nearly the same BD voltage. Only the PPLP material has a 15% higher BD voltage in the dried state in comparison to the undried state. [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]

Among various factors influencing the service life of electrical equipment, the performance of dielectric insulation materials has an important role. Degradation of insulating materials caused by aging is fatal to insulation breakdown. The dielectric sheets of most conventional and high-temperature superconducting electrical equipment are working at tensile status when lapped on the conductor. Therefore, the study of the dielectric characteristic for insulation materials at aging and tensile status is very important to safely operate electrical equipment. In this paper, a special electrode system was designed to measure the breakdown voltages of polypropylene laminated paper, polyimide, and polytetrafluoroethylene sheets at tensile status both in normal environment and liquid nitrogen. Before the breakdown experiment, the specimens of the three materials all endured the aging process of abrupt temperature change. According to the test results and the Weibull plot analysis, the polyimide presents good dielectric strength at aging and tensile status both in normal environment and in liquid nitrogen. [ABSTRACT FROM PUBLISHER]

High gradient magnetic separation (HGMS) for purification of wastewater from paper factory has been developed and withstand for 1 year operation. The system developed is a high gradient magnetic separation (HGMS) system with superconducting magnet which purifies wastewater continuously from a paper mill. The magnetic field generated by the superconducting magnet for HGMS is 2 T at the center of the bore, operating current 100 A, 680 mm long and 400 mm bore NbTi solenoid. The developed system which treats wastewater of 2000 t/day has been confirmed to show the expected performance. The purpose of the developed system is to separate COD constituents from the wastewater efficiently and economically in a small space. The required performances are follows, i) the set-up area is less than 6 m × 6 m, ii) COD of the treated water is less than 100 ppm and water can be recycled, and iii) a system can treat wastewater more than 2000 t/day. The design and the performance of the system are reported. [ABSTRACT FROM AUTHOR]

It is environmentally important to recycle the wastewater, since paper factories use a large amount of water and equivalent amount of wastewater is generated. Conventional water treatment facilities like precipitation process need large-scale equipment and wide space to purify the wastewater of paper factory. In case of massive waste water, high gradient magnetic separation (HGMS) parts are more effective to purify it rapidly and to occupy relatively small space, since large voids at filter with HGMS are adopted. In this respect, we prepared two types of superconducting magnets in order to apply HGMS parts for wastewater purification process. We made cryo-cooled Bi-2223 (HTS) superconducting magnet parts with room temperature bore in diameter of 70 mm and 200 mm in height. Also, cryo-cooled Nb-Ti superconducting magnet with room temperature bore in diameter of 100 mm and 600 mm in height was used for magnetic separator. Magnetic filters were designed by the analysis of magnetic field distribution at superconducting magnets. The faster wastewater's flow rate was, the worse the degree of clarity in treated water was. The ability of wastewater treatment in the case of magnetic separation used with 10 µm of magnetite particles was better than that in the case of 5 µm of magnetite particles. [ABSTRACT FROM AUTHOR]

Studies on developing an HTS (High-Temperature Superconducting) power cable with high transmission capacity and less loss are actively being performed worldwide. In Korea, an HTS power cable is being developed which applies cold dielectric type that a cable core wrapped by insulating papers is impregnated in liquid nitrogen. The insulating paper used in cold dielectric type is LPP(Laminated Polypropylene Paper) which has less dielectric loss and a superior dielectric property. In this paper, AC and lightning impulse breakdown strength and V-t characteristics with mini-model cables which were manufactured as the same structure with an HTS power cable were researched. Also, a thickness of insulation layer for a 154 kV class HTS power cable was designed as a result. [ABSTRACT FROM AUTHOR]

Polypropylene laminated paper (PPLP), which is used as the main insulation material of the stop joint box (SJB), has excellent dielectric characteristics in cryogenic environment. Despite excellent dielectric characteristics of PPLP, the interface between liquid nitrogen (LN2 ) and PPLP of the SJB is very vulnerable to the surface flashover. Therefore, it is necessary to investigate the surface flashover characteristics of dielectric materials including LN2 and PPLP for the insulation design of the SJB. PPLP has two orientations according to the direction of fiber in Kraft paper that are cross direction (CD) andmachine direction (MD). The research on themechanical properties of PPLP has been reported since there are differences in physical properties depending on its orientation. However, the study of the surface flashover characteristics of PPLP in the cryogenic environment according to its orientation has not been reported yet. Thus, the surface flashover characteristics of PPLP according to its orientations should be examined to ensure the reliability of the SJB connecting the high-temperature superconducting (HTS) dc cable. In this paper, the surface flashover characteristics of the PPLP in cryogenic environment in accordance with its orientation was fully investigated. The dc surface flashover tests were performed with different orientations of PPLP and various gap distances. In addition, the surface leakage currents were measured by increasing voltage at fixed gap distance. From the test results, the dc surface flashover voltage of CD was found to be 15-20% higher than that of MD. In addition, the breaking point of CD was three times higher than MD, and beyond the breaking point, the surface leakage current of CD was lower than that of MD. Consequently, the surface flashover characteristics of PPLP are significantly affected by fiber orientations of PPLP. [ABSTRACT FROM AUTHOR]

High gradient magnetic separation (HGMS) can be one of the promising ways for a new environmental purification technique because of producing no contamination such as flocculants and having possibility of treating large amount of wasted water within a short time. The magnetic separation system for purification of wastewater from the paper factory has been developed. The test plant of 2000 ton/day was set up in the actual paper manufacturing process and a purification test of the wastewater was performed. The magnetic seeding of the organic pulp and dyes were successfully performed and the Chemical Oxygen Demand (COD) value for recycling was reached to less than 40 ppm after magnetic separation. The superconducting magnet for the system is 3 T, 680 mm long and 400 mm bore NbTi solenoid. The system mainly consists of a mixing tank (magnetic seeding tank), a settling tank, and a superconducting magnet. Floating magnetic flocks composed of magnetite particles and organic polymers such as pulp and dye are captured by magnetic force in the superconducting magnet chamber. Some magnetic flocks are precipitated at the settling tank by the gravity, which helps to reduce the amount of magnetic flocks going through the magnet chamber. The system has been successfully operated for several months. [ABSTRACT FROM AUTHOR]

Purification of wastewater from paper factory was attempted by superconducting high gradient magnetic separation (HGMS) both in laboratory scale and pilot-plant scale experiments. Magnetite and some kinds of iron hydroxide particles were used as scavenging materials for suspended substances (SS) and organic dye molecules included in wastewater. The chemical oxygen demand (COD value) was used as a measure of purification of the wastewater. Optimum dosage of the scavenger was examined. Model wastewater was also prepared and tested in order to elucidate the mechanism of adsorption of the organic materials onto the scavenging particles. The obtained results showed that the wastewater was successfully purified by HGMS both in a laboratory scale and a pilot-plant scale. The apparatus modifications of magnetic filters and flow path were also made to accomplish the purification system for the practical use. The results can allow us to promote a scale-up design for greater capacity of the treatment of wastewater. [ABSTRACT FROM AUTHOR]

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]

Paper is widely used in various engineering applications due to its physical properties and ease of manufacture. As a result paper has been selected or designed as an electrical insulation material for parts and components in high voltage technology. In the current study we select a paper employed in conventional transformers as the electrical insulation material. The potential of this paper is investigated at cryogenic temperatures to determine its physical properties for high temperature superconducting power applications. Dielectric measurements were performed using impedance spectroscopy at a constant frequency. Dielectric breakdown tests were performed on samples at 77 K using a liquid nitrogen bath. [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]

Large-size aluminum alloy rings are widely used as connector, transition ring and reinforcing structure in aerospace and other fields. However, the residual stress introduced during the manufacturing process lead to the structural instability and poor mechanical properties of the aluminum alloy rings. In this paper, pulsed electromagnetic force is used to deform the aluminum alloy rings into plastic state and eliminate the residual stress in the workpieces. The residual stress in a large-size aluminum alloy ring with an outer diameter of 720 mm, a wall thickness of 60 mm, and a height of 60 mm was studied in this paper. To meet the demand of high energy input for bulging the alloy ring, an actuator coil with high voltage insulation and tough inner support was optimized designed by finite element software COMSOL Multiphysics. It was found that adding a steel ring with a truncated gap inside the epoxy skeleton can improve the compression strength of the magnet and increase the plastic deformation of the aluminum alloy ring. Besides, simulation results showed that multiple discharges can reduce the discharge voltage, which can effectively increase the service life and safety of the magnet system. [ABSTRACT FROM AUTHOR]

In addition to AC or DC voltages, superconducting electrical equipment must withstand transient overvoltages. Up to a voltage level of 245 kV, equipment has to be tested for its lightning impulse (LI) withstand voltage. Above 245 kV, the test for switching impulse (SI) withstand voltage must also be performed. These transient overvoltages are particularly demanding for compact bifilar coil windings used in resistive superconducting fault current limiters. Therefore the aim of this study is to investigate the LI and SI strength of insulating materials in tape arrangements in liquid nitrogen. Polyimide (PI), a porous insulating paper (Grade 4) and the mixed polymer PPLP (polypropylene laminated paper) in the thickness range of 125 to 130 µm are part of the investigation. The results for LI and SI show the highest values of the dielectric strength for PPLP with 203 kV/mm and 240 kV/mm. PI achieves the second highest values with 194 kV/mm as LI strength and 226 kV/mm as SI strength. With Grade 4, the lowest values are measured at 166 kV/mm and 148 kV/mm, which are, however, surprisingly high for a conventional insulating paper. Additionally, Grade 4 is the only material with a higher LI strength than SI strength. Compared to the AC strengths, the values of the impulse strengths are higher for all materials investigated, with the exception of PI, where the AC strength is in the same range as the SI strength. [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]

The paper presents a numerical study on electrodynamic behavior of the inter-pancake twin-box joints of the Poloidal Field (PF) coils of the ITER Magnet System. This work was carried out with the THELMA code, developed at the University of Bologna. The THELMA model was adapted to describe both the superconducting wires and the resistive saddle of the joint in a set of reference configurations representative of a set of experimental tests performed on a joint sample at the SULTAN facility in Villigen, Switzerland. The model was applied to analyze both the DC joint resistance measurements and the AC loss vs frequency curve, in order to obtain a full representation of the joint electromagnetic behavior. The paper reports a comparison between the numerical and experimental results and parametric studies on the impact of the main model parameters on the loss vs frequency curve. [ABSTRACT FROM AUTHOR]

Examines the use of permanent magnet for measuring the moisture content of wood chips, pulp and brown stock for the paper industry. Nuclear magnetic resonance measurement system; Accuracy of water measurement; Pore moisture and surface moisture.

This paper mainly takes a 6/4 switched reluctance motor (SRM) as an example to analyze the temperature of the motor. In order to establish the equivalent thermal circuit model (ETCM) conveniently, the mechanical structure of the motor is simplified to a certain extent, and the characteristic nodes are divided. Then the heat transfer process in the rotor region, the stator region and the whole motor during the operation of the motor is analyzed, and the ETCM of those regions are established respectively. This method of establishing ETCM is also applicable to superconducting motors. Based on the basic principles of heat transfer, the calculation method of thermal resistance in each ETCM is given in this paper. Then, the three-dimensional (3-D) finite element (FE) temperature field model of the motor is built and compared with the ETCM. Finally, the accuracy of the ETCM is verified by experiments. [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]

Battery energy storage system (BESS) plays an important role in solving problems in which the intermittency has to be considered while operating distribution network (DN) penetrated with renewable energy. Aiming at this problem, this paper proposes a global centralized dispatch model that applies BESS technology to DN with renewable energy source (RES). The method proposed in this paper aims to minimize the power purchase cost considering network active loss cost as well as voltage deviation penalty cost. Later, second-order cone programming (SOCP) method as well as big M method are applied to make the problem tractable. Last, the method illustrated in this paper is applied and validated on a modified IEEE 33-bus benchmark system to verify the effectiveness of the proposed scheduling model. [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]

For the advantages of oriented silicon steel sheet (OSSS) with better magnetic permeability in the rolling direction, this paper proposes a permanent magnet (PM) torque motor with armature teeth made by OSSS. This paper introduces the influence of unequal tooth width on the winding factor and the width calculation method of the armature teeth tip top, and analyzes the torque performance improvement by OSSS. In the end, based on testing the B-H waves of OSSS, the flux linkage, back electromotive force, rated torque and overload torque of three motors with different structure or material are compared by finite element software. The results show the proposed motor can increase the torque density and overload ability. [ABSTRACT FROM AUTHOR]

Short circuit currents show an upward trend in multi-terminal high voltage (MTHV) dc systems. DC resistive type superconducting fault current limiters (SFCLs) can limit short circuit currents to a much lower level to improve the stability of MTHV dc systems. Superconducting tapes used for dc SFCL will quench after a short circuit current attack. Then temperature and voltage of the tapes will increase. The objective of this paper is to obtain the effects of short circuit currents on quench and recovery properties of the superconducting tapes of dc resistive type SFCLs. YBa2Cu3O7-δ (YBCO) tapes was chosen as investigation samples. This paper concluded that for higher short circuit currents, the temperature and the voltage of the tape was higher. The highest temperature was 379.2 K for YBCO tapes when a short circuit current of 10 kA was applied for 50 ms. Recovery time of a short circuit current of 10 kA was 240 ms longer than the recovery time of the short circuit current of 500 A. Quenched resistance curves gotten by experiments and analysis were similar, which proved the accuracy of the analysis. [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]

In the family of the High-Luminosity LHC high order correctors, the skew quadrupole was the most critical magnet as three assemblies with different solutions were needed to meet the design specifications. This paper summarizes the prototyping phase of the magnet, discussing the observed nonconformities, the subsequent root cause analyses, and the adopted solutions. A first-hand experience showed us the importance of adopting rigorous quality assurance methods for the electrical insulation, aimed at the early defect detection, and implementing a consistent measurement-to-simulations chain for the optimization of the coils mechanical support. The improvements discussed in the paper are integrated into the final magnet design for the series production of six skew quadrupole correctors. [ABSTRACT FROM AUTHOR]

To respond to the needs of the future accelerators and the upgrade of existing machines, superconducting magnet technology is continuously evolving in the direction of high fields and high current densities. As a result, a fast and efficient quench detection becomes an essential part of the magnet design in order to safely release the stored magnetic energy during a quench. A current-based detection method was initially introduced (Dudarev 2014), is presented in this paper for Nb3 Sn Canted-Cosine-Theta (CCT) type accelerator magnets, in conjunction with the current derivative sensor that is inspired by (De Matteis 2018). The principle relies on a co-wound superconducting wire, placed beneath a superconducting cable. In case of a quench in the main cable, a transverse heat propagation will quench the sensing wire after a certain delay in the millisecond range. When the sensing wire is powered by a constant voltage source, the rise of quench resistance of the sensing wire leads to a drop in current, which can be detected by a current derivative sensor. In this paper, we describe this detection system and the test results in a subscale experiment where a quench is triggered by firing an adjacent heater strip. The advantages and limitations of this method, as well as the applicability to other magnets are also discussed. [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]

The Center Solenoid Model Coil (CSMC) is a pre-research project of CFETR, and its task is to design and manufacture the CS superconducting model coil to gain wider experience in solving the related technical problems existing in design and construction of CFETR CS coils. The expected achievement is to charge the CSMC up to the operation current of 47.65 kA and the maximum magnetic field to 12 T with a swift rump rate of 1.5 T/s without quench. Quench detection by voltage measurements is likely to be the fastest available technical solution to avoid coil's damage caused by quench, but the voltage detection is a real challenge due to large noise induced by the power supply in alternating current operation. The pick-up sensors, comprising the co-wound wire (CWW) and the co-wound tape (CWT), are used in the CSMC quench detection system for noise compensation and suppression. To accurately compensate all related induced voltage in the multi-pulse coil system, the foremost task is to estimate the static inductance matrix between the CSMC and its pick-up sensors. In this paper, a numerical model is developed for inductance calculation and analysis. Moreover, several numerical simulations with this design model to evaluate the maximum inductive noises and quench detection signals by CWW and CWT have been conducted for the case of the worst test scenarios. [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]

Solid insulation materials need to be robust in terms of both mechanical and electrical performance for application in a high-voltage superconducting apparatus. It is known that creepage discharge characteristics of solid insulation materials are inferior to their electrical breakdown characteristics with penetration. Therefore, electrical breakdown accidents in a superconducting apparatus could occur as a form of creepage discharge rather than electrical breakdown with penetration. In this study, we conduct dielectric experiments on the penetration and creepage discharge characteristics of epoxy resin and polypropylene laminated paper under cryogenic temperature by using three kinds of electrode systems. The first is for creepage discharge experiments along the surfaces of solid insulation materials in liquid nitrogen. The second is for creepage discharge experiments across the interface between two different solid insulation materialsmaking contact in liquid nitrogen. The third is for experiments of electrical breakdown with penetration on solid insulation materials in liquid nitrogen. Dielectric experiments are conducted with an absolute pressure of 0.1 MPa under alternating current and lightning impulse voltages. Experimental results for electrical breakdown characteristics of solid insulation materials with penetration are compared with the creepage discharge characteristics on the surface and interfaces between solid insulation materials. Moreover, the criteria for electric field intensities at creepage discharge voltages in various conditions are deduced as empirical formulas. [ABSTRACT FROM AUTHOR]

The ITER Central Solenoid (CS) consists of a stack of six independent coil packs called modules. It features a total height of 18 m and a diameter of over 4 m. The modules are in an advanced stage of fabrication and testing by the US ITER Project Office (USIPO) and its subcontractor General Atomics (GA). A qualification module mockup at one to one scale but of reduced height was wound and Vacuum Pressure Impregnated (VPI) by GA to validate final manufacturing, using tooling and processes fully representative of a series module. The module was submitted to a thermal cycle down to the temperature of 4.5 K at which the coils will be cooled by supercritical helium. During plasma operation, the CS modules are subjected to a complex combination of static and dynamic forces. The understanding of the mechanical behaviour of the CS module coils is of paramount importance to analyse and predict the overall response of the CS stack. To this purpose, an extensive programme of investigation of the module mockup has been defined and applied. This allowed assessing, through examination and testing of a large number of VPI conductor array samples extracted from the mockup, the soundness of the coil through advanced non-destructive examination techniques including X-ray microtomography, dimensional metrology measurements and micro-optical observations. Moreover, additional testing of physical and mechanical properties carried out at room and cryogenic temperature allowed the behaviour of the conductor stacks to be assessed. The paper summarises the results of these investigations and their interpretation through mechanical analyses based on the individual properties of the coil constituents. [ABSTRACT FROM AUTHOR]

The electron cooling technology is applied in the spectrometer ring (SRing) to improve the luminosity of ion beam for the High Intensity heavy-ion Accelerator Facility (HIAF). The electron cooler consists of a gun section, two 90-degree toroids, a cooling section and a collector section. There are four kinds of main coils used to provide longitudinal magnetic fields along the path of the electron beam. In this paper, we present the modeling and analyzing of the electron cooler magnets by three-dimension software. The optimizing of the magnetic field of cooling section is completed to achieve the required effective cooling length. The magnetic fields along the electron beam path and ion beam path are calculated and the beam trajectory of typical ion is also simulated to offer data for correcting the orbit. [ABSTRACT FROM AUTHOR]

The High Energy Photo Source (HEPS) is being built in China and the magnets are in batch production. The octupole magnets with skew quadrupole component used in the storage ring have been designed and manufactured. The octupole has an aperture of 30 mm, a field gradient of 735000 T/m3 and a length of 0.26 m. In this paper, detailed magnetic design of HEPS octupole magnets is presented. Different design schemes of the skew quadrupole coils are compared, and the temperature effect on magnetic center and the integral field in the first batch of octupole magnets are also given. In addition, the influence of the combined power-on mode on the magnetic field is studied. [ABSTRACT FROM AUTHOR]

Electrohydraulic forming is a kind of high-velocity forming process that can improve the formability of materials compared with quasi-static forming. Due to the lack of adequate material supplementation of the forming area, this method always faces problems such as uneven thinning and bursting when bulging tubes to required radial depths. To solve the above shortcomings and promote the material flow for the electrohydraulic forming process, this paper introduces an additional push coil to generate an axial electromagnetic force at the end of the tube. First, a finite element model was established to design the parameters of the push coil and the developed forming system. Then, a series of experiments using aluminum alloy tubes (AA6061-O) were conducted to verify the effectiveness of the proposed system. The results show that the limitation of the tube bulging depth can be increased by approximately 21.5%, and the thickness reduction can be reduced by more than 44% compared with conventional electrohydraulic forming. In addition, the forming morphology for tubes can be adjusted by the use of different combinations of discharge voltages for the push coil and exploding wire. The developed method and obtained results are of great value for improving the forming ability of electrohydraulic forming. [ABSTRACT FROM AUTHOR]

The High Luminosity LHC (HL-LHC) Project is planning to install 16 cold-masses made with Nb3Sn quadrupole magnets in the LHC Interaction Regions to significantly increase its luminosity. Half of these cold masses are fabricated at BNL, FNAL, and LBNL under the US Accelerator Research Program (AUP). Each cold mass includes two identical Nb3Sn quadrupole magnets, called MQXFA with a magnetic length of 4.2 m. Currently, the AUP project has completed the fabrication and test of the first 5 pre-series magnets, and is working on the following 16 magnets for the series production. The brittleness and strain sensitivity of the Nb3Sn superconducting material requires a careful definition of the allowable maximum stress in the windings during magnet assembly and pre-load, and a tight control of their variation within the whole coil length. Therefore, a series of assembly and pre-load specifications have been defined with the goals of minimizing the risk of conductor degradation and providing the mechanical support required to reach the nominal current during powering. In this paper we present the specifications defined for the MQXFA magnets and applied during the different assembly phases and during the pre-load process of the first 5 pre-series magnets. [ABSTRACT FROM AUTHOR]

Two types of nested orbit correctors are necessary for LHC upgrade, the so-called MCBXFA and MCBXFB. They share the same cross section, but feature different lengths, 2.5 and 1.5 m, respectively. The power tests performed on two MCBXFB prototypes showed excellent performance when individually powered, but training to reach the nominal torque in combined operation was very long. Moreover, memory was lost after torque direction reversal. A detailed analysis of the power test results concluded that the origin of the problem was insufficient support for the torque at the inner dipole coil ends. A fine tuning of the inner dipole design is proposed to improve the performance of both types of magnets. This paper describes the analytical and numerical models developed to analyze the problem and their results. [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]

In this paper, we propose a novel kind of Josephson Energy Suppression Pump (JESP) controlled by a fully magnetic flux drive. The device presented here is composed of two superconducting loops interrupted at one side by superconducting nanowires which are joined together by a superconducting island. The phase difference developed at the edges of the nanowires by means of the magnetic flux threading the loops can collapse their Cooper condensates, leading to complete suppression of the Josephson energies. This mechanism allows to greatly reduce the leakage current when performing Cooper pair pumping by a pure magnetic pumping cycle without involving any gate modulation. The pumping capability of the JESP is studied through a master equation approach in the non-adiabatic case. [ABSTRACT FROM AUTHOR]