Search

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]

The development of high gradient magnetic separation (HGMS) system for purification of wastewater from paper factory is discussed. Findings reveal that the system is capable of treating more than 2000 t/day.

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]

Purification of wastewater from paper factory is attempted by superconducting high gradient magnetic separation (HGMS) both in laboratory scale and pilot-plant scale. The obtained results indicate that the wastewater is successfully purified by HGMS both in a laboratory scale and a pilot-plant scale.

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]

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]

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

In order to optimize the insulation design of a cold dielectric high temperature superconducting (HTS) cable, the composite insulation system has been investigated according to the arrangement of laminated polypropylene paper (LPP) and kraft paper in liquid nitrogen. LPP is a prominent insulating material with a high dielectric strength and low dielectric loss, which has been used previously as a HTS cable insulating materials. In addition kraft paper has been used for oil-field (OF) cable as insulating materials for a long time. In this paper, the dielectric properties on composite insulation system according to the arrangement of LPP and kraft paper was compared. The economic and dielectric performances of two insulating materials were considered and applied toward a HTS cable. Furthermore, from an economic satisfaction point the most suitable arrangement, and compared the dielectric properties of the mini-model cables were examined. [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.

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]

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]

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 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]

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]

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]

Classical numerical techniques remain very computationally expensive to model the magnetization of twisted multifilamentary superconductors in three dimensions because they require solving a large system of equations. In this paper, a reduced model is proposed to approximate the ac losses of these types of wires. It is established through the projection of the physical problem in a helical Frenet basis and the use of periodic boundary conditions on a slice of the wire. The reduced model on the slice leads to systems of more reasonable size leading to smaller and faster simulations than when the whole wire is modeled. Simulation results show that the proposed method leads to computed losses similar to those obtained on a whole wire. Several simulation cases are proposed to prove the validity of the proposed model, and a comparison to some ac loss measurements is proposed to show the effectiveness of the proposed approach. The implementation relies on the H-formulation and is solved with the open-source solver, Getdp. [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]

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 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]

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 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]

Presents the recipients of various Council on Superconductivity awards. [ABSTRACT FROM AUTHOR]

This paper analyzes the asymmetrical split phenomenon of the odd and even modes in microstrip for closely coupled resonators. In general, when two resonators are coupled, the odd- and even-mode split is asymmetrical. This paper finds that, for two closely coupled resonators, odd mode always changes faster than even mode. This asymmetrical phenomenon is first predicted by using the effective capacitances of the even and odd mode. Then, the electric, magnetic, and mixed couplings are all discussed to demonstrate this phenomenon. Numerical results help us to control the odd mode in a wide range. This paper presents an ultra-wideband filter by using the interdigital coupled structure for the first time. A high-temperature superconducting filter operating at 7 GHz with −3 dB FBWs of 103% is designed and fabricated. Measured results show good performance and agree well with the simulations. [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]

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]

We have discussed dielectric characteristics of liquid nitrogen (LN2)/polypropylene (PP) laminated paper composite insulation system for the practical electrical insulation design of high temperature superconducting (HTS) cables. Focusing on the partial discharge (PD) inception characteristics and mechanism, the volume effect and its saturation on PD inception electric field strength (PDIE) was evaluated at atmospheric and pressurized condition. PD inception characteristics under lightning impulse voltage application were also investigated using an electrical and optical PD measuring system, and compared with those under ac voltage application. [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]

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]

DC fault protection is the bottleneck that restricts the development of modular multilevel converter based high voltage direct current (MMC-HVDC) system. Superconducting fault current limiters (SFCL) is an ideal protection device that can significantly limit short circuit current and enhance the fault tolerance ability of MMC-HVDC system. At present, several topologies of SFCLs have been proposed, but there is no systematical study of their current-limiting characteristics in MMC-HVDC. This paper studies the development process of DC short-circuit faults in MMC-HVDC system, and analyzes its demand for fault current limiting. Then, resistive type, saturated iron core type and hybrid type SFCL are modeled and their limiting effect of critical fault current under DC pole-to-pole fault is tested. By comparison, the current-limiting characteristics of three types of SFCL are concluded. Results show that resistive SFCL has best performance in steady state, while saturated iron core SFCL has best performance in transient state. The current-limiting characteristic of hybrid type SFCL is between the other two types. [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]

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]

Recently, the development of the electric power industry has led to an increase in the fault current when a fault occurs. It is important to reduce the fault current, since fault currents exceeding the capacity of protective devices can result in large blackouts. In order to reduce the fault current, there is a method to separate the bus line of main substation. However, this method has the disadvantage of complicating the power system. Another method is to install a superconducting fault current limiter (SFCL). The SFCL has the advantage that the fault current can be quickly limited within 1/4 cycle immediately after the fault occurrence without affecting the power system since its impedance is zero in a normal time. However, the application of SFCL affects the operation of the over-current relay (OCR) due to the reduced fault current such as trip time delay. The trip time delay of OCR was reported to be suppressed by using SFCL's voltage component in previous studies. In this paper, the impedance compensation method was suggested to exclude the effect of SFCL on OCR. To prevent OCR from the influence of SFCL, the component that can exclude the impedance of SFCL was considered to be added to the characteristic formula of OCR. In addition, the effect of correcting this characteristic equation was analyzed by constructing a power distribution system using PSCAD / EMTDC. [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]

High-temperature superconducting (HTS) maglev system, based on the magnetic flux pinning characteristic of non-ideal type II superconductors, can realize self-stable above permanent magnets. HTS maglev possesses the advantages of low-energy consumption, simple mechanical structure and environment-friendly, which make it an ideal high-speed transportation mode. When an HTS maglev vehicle crosses a ramp, the levitation height will fluctuate due to the rapid change of the track curve, which may affect the safety and stability of the system. In this paper, first, a levitation force model was obtained based on experimental data. Based on this model, a dynamic model of the HTS maglev vehicle-bridge coupled system was established. The dynamic response of the maglev train was simulated and analyzed when it operated through track grade change points under different track slopes, vertical curve radii and speeds. The influence of these parameters on the stability of the system was investigated, and the optimized design parameters for the vehicle and the track slope are proposed as well. This study provides references for the future engineering development of HTS maglev transportation. [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]

The high temperature superconducting (HTS) cable has shown promising prospects in megacities for the advantages of high transmission power density and low loss. However, when HTS cable is working on grid, various kinds of faults may cause irreversible damage, resulting in the failure of reclosing. In this paper, the resistive superconducting fault current limiter (R-SFCL) is introduced into the power system to cooperate with the HTS cable, so as to reduce the potential damage caused by fault current. Firstly, the equivalent circuit models are established, and then transient response of HTS cables under fault condition is analyzed, the recovery time of HTS tapes are used to define the design of R-SFCL. Finally, the operating reliability of HTS cable has been evaluated and measures about adaptive reclosing times were proposed under different fault currents. [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]

This paper presents an electromagnetic design of a permanent magnet superconducting wind power generator with different stator teeth structures and armature winding arrangements. The main contribution of this paper is that a novel stator configuration is proposed, which is beneficial for superconducting machines. The topology of tapering poles makes it possible for the machine to carry larger current without severe magnetic saturation in the stator teeth. Meantime, the distributed arrangement of wires in the stator slot can reduce the ac loss in the same output power condition. Finite element analysis with commercial software is used to support these results. [ABSTRACT FROM AUTHOR]

With the growing use of wind power in power systems, the requirements of low-voltage ride-through (LVRT) have been proposed. Yet, all LVRT strategies commonly used in the doubly fed induction generator (DFIG) tend to change its running state, which brings a secondary impact to the transient stability of the system. This paper combines the output power of the DFIG with the equivalent mechanical power of the system, deducing the mathematical relationship between them, and theoretically analyzes the relationship between superconducting magnetic energy storage (SMES) access location and transient stability improvement. On this basis, this paper puts forward an SMES coordinated control scheme considering location information to improve the dynamic characteristics of grid-connected wind farm, achieving higher transient stability performance of the system. Finally, the simulation in MATLAB/Simulink verifies the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Nonuniform electric field distribution is one of the key issues for the superconducting cable terminals. This paper tries to modify the electric field distribution in HTS dc cable terminals by the nonlinear conductive epoxy/ZnO insulation, instead of the insulation with a fixed conductivity. The nonlinear conductivity of epoxy/ZnO composites is measured, and a finite element simulation model of the +100 kV HTS dc cable terminal is established to analyze the electric field distribution at the steady and transient state. The results show that the field-dependent conductivity has a great effect on the dc electric field distribution. If the nonlinear coefficient is excessively large, the electric field in the polypropylene laminated paper (PPLP) will be extremely strong; otherwise, the electric field in the terminal insulation will be extremely strong. The epoxy/ZnO composites with an appropriate nonlinear conductivity can effectively uniform the electric field distribution at the triple-junction and the stress cone surface. When the switching overvoltage impulse superimposed dc voltage is applied, the maximum field is always located in the cable insulation of PPLP, which is because that the electric field distribution in the stress cone is mainly dependent on the capacitance characteristics of the insulation instead of the conductivity. The nonlinear conductive epoxy/ZnO composites could play an important role in promoting the development of stress cone of HTS dc cable terminals. [ABSTRACT FROM AUTHOR]

Quench and recovery characteristics are the most important characteristics of dc resistive type superconducting fault current limiters (SFCLs). In the normal state, the superconducting tapes of SFCLs stay in superconducting state without power loss. However, if there is a thermal disturbance energy impact to the superconducting tapes, the tapes may be quenched, and sometimes even break once their temperature is too high. After the thermal disturbance, the tapes may recover to superconducting state again. A numerical analysis method was proposed to analyze quench propagation and recovery characteristics of the YBa2Cu3O7-δ tapes based on thermal conduction theory. The objective of this paper is to obtain the influencing factors such as magnitude of thermal disturbance, transport current, material of the stabilized layer and cooling on quench, and recovery properties of dc resistive type SFCL. Numerical analysis results show that the temperature and voltage of the tape increased while the transport current through the tape and the magnitude of thermal disturbance increased. The quench propagation velocity was higher and the recovery time was shorter for copper stabilized layers than stainless steel stabilized layers. [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]