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The plasma confinement of the International Tokamak Experimental Rector (ITER) is provided by the magnetic field generated by 18 toroidal field (TF) coils while 6 poloidal field (PF) coils have the function to shape and pre-heat the plasma. Fusion for Energy (F4E), the European Domestic Agency for ITER, is responsible for the supply of 10 TFC and 5 PFC to the ITER project. The ITER Organization (IO) team is instead responsible for the design of such coils as well for the coordination of the activities of the different Domestic Agencies (DA) producing the different components for the Tokamak.
The PF coils utilize NbTi Cable-in-Conduit-Conductor and have different diameter ranging between 7 and 25 meters and a weight up to 400 tons. Regarding the PF coils produced by F4E, so far one has been completed by the the Institute of Plasma Physics Chinese Academy Of Sciences (ASIPP) under a collaboration agreement with F4E. The other 4 PF coils are being produced at the ITER site (Cadarache) under F4E supervision: the first PF coil (PF5) will be completed by June 2020 while the last coil (PF3) will be ready be the end of 2023. The TF coils utilize a Nb3Sn conductor and are manufactured with the “Wind, React & Transfer” method. The first TF coil is close to its completion and it will be delivered to ITER by begin of 2020, while the others TF coils will follow with a rate of about one every 3-4 months. In this article we will report on both PF and TF coils, in particular on the different utilized manufacturing strategies, the main challenges faced so far and the results obtained.
The DDT (Divertor Tokamak Test) machine is under construction at the Frascati research center of ENEA and is aimed to investigate the possible divertor solutions for the management of power and particles exhaust for the EU-DEMO tokamak. Its Poloidal Field coil system is constituted by 6 magnets, identical in pairs as the machine is foreseen to be fully symmetric to allow for plasma configuration in the single null (SN) as well as in the double null (DN) scenarios. The PF1 and PF6, will be wound by Cable-in-Conduit conductors (CICC) cabled with Nb3Sn strands, answering to the request of magnetic fields up to about 8 T, as well as to reduce their occupancy in favor of mechanical structures and to leave room for the large ports at the polar regions, while the PF2/5 and PF3/4 are designed with NbTi CICCs, being the project request in terms of field less stringent.
The Divertor Tokamak Test facility (DTT) is an experimental tokamak machine to be built in Frascati, Italy, at the ENEA research centre. During its development, the DTT has gone through several important design updates. Developing a rigorous finite element methodology to evaluate the performance of all its components has thus been a critical part of the verification phase of each new design iteration. This work summarises the outcome of the structural analyses that support the current design of the Toroidal Field (TF) magnet system, including the superconducting winding pack ($Nb_3Sn$), the casing structure and all of the inter-coil structures. Given the high complexity of the 3D structure to reproduce, some modelling simplifications were mandatory to solve the problem. We hereby describe the finally adopted methodology next to all the motivations we examined to make sure the results were sound and reliable from an engineering point of view.
In the EU DEMO fusion reactor, currently in its pre-conceptual design phase, the long plasma pulse duration and the large thermal loads represent a challenge for the power exhaust, so that a new, robust design of the divertor is needed. For this reason, several DEMO-relevant divertor solutions will be tested in the Divertor Tokamak Test (DTT) facility that will be built in Italy. It will be a fully superconductive compact tokamak, very flexible in terms of plasma configurations.
The 18 Toroidal Field (TF) magnets, cooled by forced-flow supercritical helium at 4.5 K, must then be reliable components, capable to cope with several different operating scenarios. To protect them (and the entire machine), the possibility of a fast discharge of their magnetic energy by means of dump resistors is foreseen.
The 4C code, aimed at the analysis of thermal-hydraulic transients in superconducting magnets, is used here to develop a detailed model of the DTT TF coils. The model will be used to analyse parametrically the fast discharge and optimize the dump time constant. The latter will indeed be limited by two main constraints: on the one hand it must be sufficiently large not to develop a voltage that can damage the electrical insulation, with a serious impact on safety and reliability aspects which are fundamental for an expensive nuclear fusion experiment; on the other hand, the heat deposited by AC losses in both cable and supporting structures during the current and magnetic field variation can lead to a quench, so that it is desirable to reduce the transport current as fast as possible to reduce the hot spot temperature and thus the thermo-mechanical stresses possibly damaging the cable (and, again, impacting on the magnet system reliability). An optimum range for the dump time constant is then proposed as a guideline to the magnet system designers.
In the context of the European Fusion Roadmap, the Divertor Tokamak Test (DTT) experimental reactor is intended to investigate alternative divertor configurations in view of the EU-DEMO power exhaust handling necessities, and it is to be built at the Frascati ENEA research centre in Italy. The six poloidal field coils of the tokamak are responsible for the plasma shape and equilibrium, and numerous steps were taken to obtain a design that is magnetically consistent with the plasma requirements and structurally compliant with the chosen failure criterion. All the poloidal field magnets are superconductive and comprised of $\rm{NbTi}$, except for the uppermost and lowermost coils which feature $\rm{Nb_3Sn}$ as superconducting material. This work presents the structural assessment that has been performed on the poloidal field coil system, taking into account the cooldown process, the energisation to operating conditions and fatigue. Finite Element Analysis has been employed as the principal means of investigation, while some classical results from the theory of Elasticity corroborate the evaluations.
To optimize the amount of superconductive material, each module is divided into two submodules. The innermost submodule operates in a range of 10/14 T, while the outer one at 10/6 T.
The design of DEMO PF coils is proposed and analysed based on the requirements defined by the EUROfusion 2019 DEMO baseline. Two types of forced flow cable-in-conduit conductors are used: NbTi with high void fraction and Nb3Sn with a dedicated cooling channel. The design addresses the dimensioning of the winding pack, the electromagnetic field calculations, stress analysis and thermal hydraulic and quench propagation analysis. The amount of structural material depends mainly on the hoop load. This is verified by fatigue stress analysis. The amount of superconductor, copper and cable void fraction (or cross-section of cooling channel) are determined by the temperature margin and quench analysis. The AC loss is modelled with conservative assumptions. The new design fulfils the design criteria set by the 2019 DEMO baseline. For some coils, the comparison of NbTi and Nb3Sn design options suggest more efficient allocation of structural and superconducting material in the latter case. It is also verified that temperature margin is always above 1.5 K.
The high-grade Nb3Sn TF conductor, operating at 63 kA and 12.4 T (Tcs >6.5 K) was tested at SPC, and afterwards was used for fabrication of inter-layer joint. The developed TF inter-layer joint is an “overlap-type” joint, which can be fit within the dimensions of TF winding pack. Each end of two conductors is copper cladded by a plasma-spraying technique and bonded together over the surfaces of cladded copper by a high-frequency inductor.
State-of-the-art high field solenoids make use of hybrid designs exploiting the superior high field performance of High Temperature Superconductors (HTS) in the innermost region. The benefits of a hybrid Central Solenoid in a pulsed tokamak like DEMO can be two-fold: either to reduce its outer radius (which would result in a reduced overall size and cost of the tokamak), or to increase the generated magnetic flux (which could extend the plasma burn time and possibly increase the power plant efficiency). In the framework of the pre-conceptual design studies for DEMO coordinated by EUROfusion, a hybrid Central Solenoid is proposed based on ten layer-wound sub-coils using HTS, Nb3Sn, and Nb-Ti conductors respectively for the high, medium, and low field sections. The design exploits the flexibility of layer winding by grading both the superconductor and the stainless steel cross sections in each sub-coil, which has the potential for significant space and cost savings. Mechanical analyses have identified fatigue as the main design driver for the EU DEMO Central Solenoid. Possible alternatives to reduce the sensitivity of the proposed design to fatigue are currently under investigation.
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
Second-generation high temperature superconductors (HTS) are available for producing >25 T at magnet bore compared to 16 T for low temperature superconductors (LTS) magnets proposed in recent studies of the Fusion Nuclear Science Facility (FNSF), thus enabling higher fusion power density and a smaller device size. High current density is required for engineering design of the next step FNSF to allow space for interior plasma components. PPPL is teaming up with US industry in developing the compact high field central solenoid (CS) insert design made with high current transposed cable comprised of mechanically enhanced Bi-2212 wires. This collaboration is aimed at demonstrating the feasibility of producing a small (a few centimeters diameter) but high field HTS solenoid insert that meets the challenging fast current ramp rate and low AC loss requirements while maintaining high current density needed for the low aspect ratio ST FNSF pilot plant design.
The prototyping and small coil testing plan developed will demonstrate maturity of the enabling Bi-2212 wire technology desired in ~20T high field prototype coil for fusion pilot plants. The goal is to demonstrate design of small CS insert solenoid coil for plasma startup while maintaining a low fabrication cost, for solenoid coil winding using directly commercially available Bismuth strontium calcium copper oxide (Bi-2212) strands to achieve 20T high field on coil and 1-2 Wb flux swing therefore, validating maturity for compact fusion magnet design, prototyping and testing. The plan includes production of small Bi-2212 of solenoid prototype coil, and prototype coil testing.
The goal of the Gas-Dynamic Multimirror Trap (GDMT) project is to create a multi-functional experimental facility and lay the groundwork for future development of fusion applications of open-ended magnetic plasma confinement systems with linear axisymmetric configuration. Among the most promising plasma confinement concepts to be studied on this facility are the diamagnetic plasma confinement mode and plasma flux suppression by multimirror and helical magnetic sections [1].
The conceptual design of the GDMT installation is under development and assumes a modular construction principle, which allows the installation to satisfy the requirements of the experimental program. Regarding the magnetic system of GDMT, this means that it must be built from several types of universal modules, which could be assembled in a particular order according to demands of the experiment. By utilizing this approach and controlling the current in each of superconducting coils, which make up the modules, it is possible to facilitate a transition from one magnetic configuration to another. The confinement region of the magnetic system is a several meters long solenoid with diameter of magnetic coils ~ 1.3m and axially uniform magnetic field. A certain experimental scenario requires that the magnetic field be ramped up from 0.3 to 3 T within 5 seconds, which implies than a special low AC-loss superconducting cable must be chosen for this part of the installation. In this paper we present the requirements for magnetic field distribution, preliminary calculations and a general appearance of the superconducting magnet system, along with an assessment of the parameters of superconducting materials necessary to create such a system.
The conceptual design for the superconducting coils of the K-DEMO tokamak has been proposed and continues to be updated. The toroidal field coils rely on Nb3Sn technology with new generation high Jc strand. The design is that of a cable-in-conduit conductor (CICC) consisting of multistage Nb3Sn cable inside a rectangular stainless steel jacket. There are huge Lorentz forces on the cable due to the large currents and magnetic field. A large aspect ratio for the rectangular conductor is proposed to reduce the accumulative pressure on the cable strands. Further increases in the aspect ratio would be advantageous. However, manufacturing such a conductor in a conventional way would be difficult as compaction of a cable to extreme aspect ratios damages the strands. To overcome this limitation, an alternate cable design for the conductor is proposed. The perceived advantages and expected difficulties and required complications of the design are discussed.
Conceptual design studies of the helical fusion reactor FFHR-d1 are progressing at National Institute for Fusion Science (NIFS) for realizing steady-state fusion energy production. The continuously wound helical coils have the major radius R of 15.6 m, four times that of the presently working Large Helical Device (LHD) with R = 3.9 m. The High-Temperature Superconducting (HTS) large-current capacity conductor, named STARS (Stacked Tapes Assembled in Rigid Structure), has been developed to be applied to the helical coils of FFHR-d1. The operation condition is 100 kA current at 14 T magnetic field and 20 K temperature. The current density of the conductor is set at 25 A/mm2.
The FFHR Design Team has been investigating several types of High-Temperature Superconducting (HTS) large-current capacity conductors to be applied to the LHD-type helical fusion reactor FFHR-d1 (major radius R = 15.6 m). Presently, before realizing this commercial fusion reactor for electricity production, smaller reactors FFHR-c1 (R = 10.92 m) for DEMO and b1 for volumetric neutron source are being designed. For FFHR-b1, the target values of the current and current density are 10 kA and 120 A/mm$^2$, respectively, at the magnetic field of >16 T and temperature of ~20 K on the conductor. A new manufacturing method called “Wound and Impregnated Stacked Elastic tapes, WISE”, has been invented as one of the candidate conductors. In this concept, stacked HTS tapes are inserted into a flexible metal tube to form a conductor, and wound onto a coil frame, and then impregnated with low-melting metal. In the flexible metal tube, each tape naturally deforms so as to minimize the strain forces. The low-melting metal stabilizes the conductor from two points of view: good cooling efficiency and uniform current distribution among tapes and windings by utilizing the no-insulation (NI) technique.
A sample coil using the HTS-WISE conductor was fabricated to prove the feasibility of the WISE concept. Ten REBCO tapes of 4-mm width were inserted into a stainless-steel tube and wound to shape a solenoid coil. The major specifications of the coil are 21.5 turns with a minimum winding radius of 40 mm, and 30 µH of inductance. The coil achieved a central magnetic field of 0.16 T at 77 K, having an 800 A current (15 A/mm$^2$) in steady-state. Despite the appearance of an electric field of ~1 mV/m along the conductor, quench did not occur. In the presentation, the details of the NI-HTS-WISE magnet concept is discussed.
In this article, we presented a technical design of the superconducting Dipole magnet, H-type like the SAMURAI magnet at RIKEN, for the Lithium(Li) alloy, the material of first wall of ITER Demo, magnetofluid behaver study, depending on mechanics, thermal and electromagnetic multi-field couple analyze results. Each coil has 1998 turns, with the inner diameter was 1.5m. The wire has NbTi filaments with a total Cu/SC ratio of about 8 in the conductor. The operating current and the goal of central field are 425A and 3.0T, within 1000mm×1000mm×300mm(L×W×H) regions the inhomogeneity of the field is less than 5%, and the maximal magnetic field (Bmax) is 4.3T in the coils, respectively. The vertical magnetic force in the coils is about 200 tons, and the maximal hoop stress and radial stress of the coils are about 90MPa and 10MPa, theoretically. Meanwhile, magnetic quality and coil’s stress state affected by the assembly error and welding deformation of the magnet former are systematical analyzed, moreover dependent on the previous correlation results, we optimized the manufacture and assemble parameters to reduce the cast. And the cold mass of each coil is suspended from the room temperature vacuum vessel by six Titanium alloy suspension links. The magnet, with energy stored in the magnet is about 5 MJ, will be self-protecting. However, in order to limit the temperature, current and voltage value under a reasonable value in case of a quench, multi-segments protection method was employed. Now, the magnet is under construction, and as expected the test results will be reported.
JT-60SA is a fusion experiment tokamak device using superconducting magnets to be built in Japan. This joint international project involves Japan and Europe. In this work, we presents the design of cryodistribution and its components which are composed of a main transfer line (TL) and valve boxes (VB).
Five coolant loops are distributed between a helium refrigerator system (HRS) and cold components. Super critical pressure helium (SHe) of 4.5 K and 0.5 MPa supplied to 18 toroidal field coils, 6 equilibrium field coils and 4 central solenoid modules (LOOP1 & 2). SHe of 3.7 K and 0.5 MPa is supplied to divertor cryopumps (LOOP3). Gaseous helium (GHe) of 80 K and 1.4 MPa is supplied to radiation thermal shields (LOOP4). GHe of 50 K and 0.4 MPa is supplied to cold ends of high temperature superconducting current leads (LOOP5).
TL is a vacuum heat-insulation multiple piping, of which the length is about 45 m, and connects between HRS and the tokamak cryostat. All 5 supply lines, 4 return lines and 2 control valves are installed in TL. The outer vacuum pipe diameter is 965.5 mm and the inner coolant pipe diameter are 108.3 mm for LOOP 1/2/4 and 59.0 mm for LOOP 3/5. A vacuum partition between HRS and the tokamak cryostat is located near the middle of TL in a longitudinal direction.
VB contains cryogenic valves and measurement devices to control the cold helium flow. Eleven VBs are installed around the tokamak cryostat. Dimensions of VB body are 2 m in height and 1.4 m in diameter. Almost all cold helium lines from HRS are firstly into VBs through TL. Impulse lines, orifice plates, and resistor elements are installed at the pipes in VB for measurement of the pressure, the flow rate, and the temperature of coolant helium.
JT-60SA is one of the experimental nuclear fusion reactors with superconducting magnets. It is a joint international research and development project involving Japan and Europe. The transitional change of temperature distribution of these magnets in recovery from the coil quench is investigated.
The quench recovery period is necessary to be confirmed. Generally, the maximum temperature drop of magnets is able to be confirmed by checking the thermometer attached to the outlet of the helium flow path. However, the maximum temperature of the JT-60SA central solenoid (CS) is not able to be measured during quench recovery. A CS module is composed of the 52 layers pancake coils. The 26 helium flowing paths are in a one module and two pancake coils are cooled in series in one flow path. The refrigerator supplies helium at 4.4 K to each flowing path in nominal operation.
In case of a quench, the refrigerator stops helium supply in order to shut out large heat load from the quenched magnet. Helium will be supplied again when the magnet pressure become low enough. In this work, the CS temperature distribution change during quench recovery is calculated by using the thermal fluid simulation codes, and the period required for recovery is investigated.
EAST (Experimental Advanced Superconducting Tokamak) has been carried out fourteenth campaigns since its implementation at the end of 2005. The cryogenic system is one important subsystem which is to cool down the superconducting magnets and relating components. Alarm and interlock system ensure the reliability and safety of cryogenic system. This paper presents the overview of the alarm and interlock system, especially in quench protection in cryogenic system of EAST. At same time, the operational performance has been analyzed with further purpose to improve the cryogenic system reliability so as to guarantee the success of high performance plasma experiments in future.
With the development of superconductivity technology, more and more large scale superconducting coils or magnets are used in the scientific installation like tokomaks, particle accelerators and colliders. Before installation, each coil is needed to cold test at nominal operating current to minimize the risk of malfunction. Hence, a helium refrigerator with an equivalent cooling capacity of 5 kW at 4.5 K for large scale coil test facility is proposed. It can provide 3.7 K, 4.5 K supercritical helium for coil, 50 K cold helium with a 10 g/s flow rate for High Temperature superconducting (HTS) current leads and 50 K cold helium with a cooling capacity of 1.5 kW for thermal shield. This article presents the conceptual design of cryogenic system for large scale superconducting coil test, including system process, thermal cycle, operation modes, compressors station system, cold box, distribution system and cryogenic control system.
A proton therapy facility with multiple treatment rooms based on superconducting cyclotron scheme is under development in HUST (Huazhong University of Science and Technology). This paper will introduce design and development of the beamline system that convers the ESS (Energy Selection System) section based on an energy degrader, the gantry beamline with image optics, and a kicker system which performs fast beam switch during spot scanning. Design, construction and magnetic field measurements of beamline magnets, including dipoles, quadrupoles and the kicker magnet will be described. A lightweight superconducting gantry beamline with alternating gradient (AG) combined function dipoles, which is planed for future upgrade, will also be discussed.
We proposed the air-core cyclotron using high-temperature superconducting (HTS) technology, named Skeleton Cyclotron, as high intensity compact cyclotron. Skeleton Cyclotron consists of split main coils generating the isochronous field and sector coils generating the azimuthally varying field (AVF). Rapidness and reproducibility of magnetic field change for various particle and various energy are improved. Currently, we are carrying out a feasibility study on a variable-energy multi-particle Skeleton Cyclotron for medical radioisotope (RI) production. It is necessary to develop the following HTS magnet technologies for Skeleton Cyclotron: 1) the no-insulation (NI) winding technique for high current density and high thermal stability; 2) reduction method of screening current for highly precise magnetic field and optimal operating current pattern for temporal stability of magnetic field; 3) our proposed Y-based Oxide superconductor and Reinforce Outer Integrated (YOROI) structure with a high mechanical strength structure for circular and noncircular coils; and 4) optimal configuration design of HTS multi-coil system. Therefore, the small model HTS coil system to generate the magnetic field for accelerating proton up to 5 MeV of energy at an extraction radius of 20 cm is designed and manufactured to verify the key issues in HTS magnet technologies for Skeleton Cyclotron. In this presentation, the design and progress in development of the small model HTS coil system is reported.
The scanning magnets in the proton therapy nozzle control the deflection of the proton beam by changing the magnetic field, so that the position of the proton beam can be controlled precisely, within 0.5mm error at lateral and longitudinal position. In order to meet the requirements for precise control of the beam position, a multiple redundant adaptive PID control system for scanning magnets is designed based on LabVIEW in this paper. It monitors the current of the scanning magnet coil and the actual magnetic field at the same time, then controls the output of the scanning magnet power supply separately through closed-loop positive feedback calculation, so that the entire magnetic field control system can maintain normal operation. And the fuzzy-PID control technology is added in the closed-loop program to improve the system response speed and adaptive computing ability, also increase the stability of the system.
A rotating gantry enables charged particles to be delivered to a tumor with great accuracy in heavy particle therapy. Hence, cancer therapy that does not damage a patient can be realized with a rotating gantry. The world’s first rotating gantry composed of superconducting magnets was developed in the National Institutes for Quantum and Radiological Science and Technology in 2015. Using superconducting magnets instead of conventional magnets, it became possible to make a lighter, smaller rotating gantry.
The superconducting magnet for the rotating gantry consists of a cosine-theta superconducting coil surrounded with an iron yoke which is the heaviest part of the magnet’s weight. The weight of one superconducting magnet reaches several tons, and the rotating gantry is composed of ten superconducting magnets. Accurate rotation control is required under the condition that the magnets of several ten tons are mounted on the frame of the rotating gantry. In this study, a superconducting magnet composed of an active shield coil for the gantry has been proposed for the purpose of simplifying the control system and the frame structure of the rotating gantry by reducing its weight. The magnet’s weight can be reduced by using an active shield coil instead of an iron yoke to shield the leakage magnetic field. The lightweight design of a superconducting magnet with active shielding for a rotating gantry is presented.
A previous study in our group showed the possibility of local accumulation of the ferromagnetic particles on the rotation axis 25 mm away from a magnetic field source by using a high-frequency rotating magnetic field. In order to put this therapy into practical use for cancers located deep in the body, it is necessary to accumulate the particles at a target site about 300 mm away from the magnetic field source. In this research, we propose an application method of the rotating magnetic field by utilizing four superconducting magnets and a cylindrical magnetic shielding material with a slit. In this method, the four superconducting magnets are excited at the same time, and the rotating magnetic field is applied by the leakage magnetic field from the slit of the rotating shielding material. Accordingly, we designed a rotating magnetic field that can locally accumulate the particles at the target site 300 mm away from the magnetic field source and examined the possibility of particle accumulation by the simulation based on magnetic field and fluid analysis and the model experiment by using simulated organ.
Adaptive genetic algorithm is adopted to globally optimize the key parameters of the transcranial magnetic stimulator including coil turns, layers, hollow diameter as well as temperature and minimum flow velocity of cooling water. Optimal design of transcranial magnetic stimulator is obtained with minimum power loss and satisfies both medical needs and heat dissipation requirements. Finite element analysis is adopted to obtain three-dimensional spatial distribution of the intracranial induced electric field. Results show that compared to traditional magnetic stimulator without considering heat dissipation, this novel transcranial magnetic stimulator design can work continuously under the premise of guaranteeing the stimulation intensity and focalization.
Since the rotor is supported by mechanical bearings, the mechanical friction and wear exist in the conventional wind turbine inevitably, which not only increase the starting wind speed and the maintenance cost, but also reduce the efficiency of power generation and the operation stability. In order to overcome these disadvantages, a magnetic suspension wind turbine (MSWT) is proposed. Nowadays, the MSWT has been extensively investigated all over the world due to the advantages of low starting wind speed, high power generation efficiency, low maintenance cost, no friction, no lubrication, and so on. However, some defects limit its development. For example, the application of magnetic bearings increases the axial length of the system, limits the critical speed, and generates great suspension power consumption. The introduction of a bearingless generator to replace the wind turbine supported by magnetic bearings can effectively solve these problems. To realize the design objectives of high generation performance and stable suspension capability, the multiobjective optimal design of a bearingless permanent magnet synchronous generator with multiobjective particle swarm optimization (MOPSO) algorithm is carried out in this paper. Firstly, the torque and the suspension force performances of each design factor combination are analyzed by finite element analysis (FEA) method according to the central composite design scheme. Secondly, in terms of the results of FEA, the response surface method is applied to obtain the regression equations of the optimization objectives with respect to the design factors. Thirdly, with the response surface models as the objects, the Pareto front is obtained by the MOPSO algorithm. Finally, the Pareto optimal results are analyzed in the FEA software and the validity of the design scheme is verified.
In this study, the design and experiment of high-speed PMSG using magnetic bearing without mechanical friction was carried out. The rotor size of the PMSG is designed by considering the DN factor of the bearing, and has a rotor diameter larger using magnetic bearings than that of the rotor diameter using ball bearings. Increasing the size of the rotor will reduce the stator copper loss and rotor eddy current loss due to the increase of magnetic field, but the increase of the core loss. Furthermore, stress analysis of permanent magnets and sleeves should be performed as a result of the increase in rotor size. Thus, in this paper, the high-speed PMSG with magnetic bearings is presented a design method considering the improvement of the conventional electric machine design technique from an electromagnetic point of view and the securing of structural reliability of rotor. The validity of the proposed design method was verified by the electromagnetic and mechanical analysis, design and comparison with experimental results of the high speed PMSG of 124 kW, 36 krpm. The design criteria, analysis results, and measurements of the high-speed PMSG will be presented in more detail in the final paper.
Owing to their many advantages, such as high efficiency, high power density, simple mechanical construction, no excitation loss, and good reliability, high-speed permanent magnet synchronous generators (PMSGs) are gaining considerable attention from academia as well as industry worldwide. Because of the high-magnitude centrifugal forces that are exerted on the permanent magnets (PMs) in high-speed PMSGs, a robust rigid rotor construction is paramount. In particular, to protect the PMs in the rotor, the surface of rotor is coated with a retaining sleeve constructed from either an alloy or carbon fiber. Furthermore, a high-strength material is used for the shaft coupling component of the PMSG because of the stiffness of the shaft. Nevertheless, because this high-strength material might possess magnetic properties itself, it can influence the electromagnetic characteristics in the end effect. Moreover, the winding reactance includes significant leakage reactance because of the robust rigid rotor structure. Therefore, it is important to accurately calculate the total leakage reactance for the electromagnetic evaluation of high-speed PMSGs. In this study, an accurate analysis to determine the electromagnetic parameters of high-speed PMSGs is proposed; in addition, the influence of the rotor structure on the electromagnetic performance of these generators is analyzed. Because finite element (FE) analyses capable of solving transient models that include rotational and external circuits are now widely available, using these advanced computational methods, it is possible to determine the electromagnetic performance of the generators considering realistic features such as saturation, magnet segmentation, and end effects. In particular, in contrast to the existing 2D FE analysis approach, the electromagnetic parameters that are influenced by the rotor structure have also been identified and included in our proposed approach to accurately predict the electromagnetic performance of high-speed PMSGs. Finally, the efficacy of the proposed method is evaluated using 3D FE analysis and experimental verification.
Wed-Mo-Po3.05-04 [31]: Experimental Verification and Analytical Prediction for Generating Characteristics of Double-Sided Permanent Magnet Linear Synchronous Generator for Ocean Wave Energy Converter
For permanent magnet (PM) linear generators to be applied to ocean wave energy converters, highly efficient energy conversion is important; however, for maximum power generation, wave motion variation must be treated in real time. Therefore, we propose a characteristic map of the generating performance, including characteristic results of power, losses, efficiency, force, and the power take-off (PTO) damping coefficient. The conditions for optimum performance and the range of maximum power generation can be obtained from these results. Furthermore, when regular wave energy is generated, the heaving motion of the buoy is changed by the PTO damping coefficient from the PM linear generator, and the input velocity of the PM linear generator is thereby affected. Therefore, selecting the condition for maximum power in regular wave energy is vital for ocean wave energy converters.
In this study, a three-dimensional (3D) analysis method and a manufacturing model are used for analysis of generating performance and experimental verification on a double-sided PM linear synchronous generator (PMLSG) with a slotless stator. The initial design was devised using the 3D analytical method, which reduced analysis time and provided increased reliability. In addition, no-load performance was verified through experiments on the manufactured model. And then, under an ac-load, we determined the generating characteristics of the PM linear generator, with the heaving motion of the buoy coupled with the generator according to ocean wave variation. Finally, we addressed the generating results of the PM linear generator for the ocean wave energy converter according to the irregular input wave. In the detailed manuscript, we present a simple summary process of the 3D analysis method and various experimental results of the manufactured model; and all the analytical procedures are specially designed to contribute to related research and industrial applications.
Wed-Mo-Po3.05-06 [33]: Research of Post-Assembly Magnetization of Large Surface-Mounted Rare-Earth Permanent Magnet Machines with Integrated Magnetizing Windings combing with Stator Windings
With the power increasement of permanent magnet (PM) machines, the manufacture process and maintenance of irreversible demagnetization become increasingly difficult, which limits the magnetic field configuration design of large PM machines. Post-assembly magnetization method is the key to solve these problems and can improve the machine performance. One way is adding additional integrated magnetizing winding. The magnetizing coils are directly wound around the un-magnetized PMs, and mounted on the surface of the rotor together. The PM machine can be magnetized after completely assembly by energizing the magnetizing winding with a pulsed magnetizing current. However, it is not easy to obtain high enough magnetizing field while ensure the insulation and reinforcement of the magnetizing winding due to the limited space between adjacent PM poles. A hybrid magnetization method using additional integrated magnetizing winding combing with machine"s own stator winding for a megawatt PM wind generator is presented in this paper. The parameters of the magnetizing winding are designed. The parameters of the magnetizing circuit and the discharge sequence and field proportion of the magnetizing coil and stator winding are optimized to obtain the minimum magnetizing field required for saturated magnetization. The impact of inverse eddy current in PMs and the coupling effect between magnetizing winding and stator winding are analyzed. The problem of weakness of local magnetizing field caused by stator slotting is solved by using magnetic slot wedges. The simulation results show that the magnitude and uniformity of the composite magnetizing field meet the requirements, the ampere turns required is reduced compared with the method of using additional magnetizing winding only. Moreover, the temperature rise and stress of the magnetizing winding are acceptable. It is indicated that the large surface-mounted PM wind generator can be post-assembly magnetized with the magnetization method proposed in this paper.
Wed-Mo-Po3.05-07 [34]: Detent Force and Static Thrust Experimental Analysis of a 3kW Single-Phase Linear Permanent Magnet Generator for Striling Engines
Despite these advantages, the linear generator has the disadvantage that it is very difficult to evaluate due to its reciprocating linear motion. Also, unlike rotating machines, it is not easy to evaluate the detent force of a linear generator and to evaluate the output power of a linear generator.
Recently, eco-friendly vehicles such as pure electric vehicles (EVs), hybrid EVs and plug-in hybrid EVs (PHEVs) have been the subject of many studies in a dramatically accelerated effort to increase the total driving distance on a single charge. Among of PHEV components, increasing the efficiency of the engine generator system (EGS) is a key challenge in this effort. In the EGS, a generator and an engine are mechanically linked, where the generator is operated from output power of the engine while the PHEV is operating. In order to increase the efficiency of EGS, the generator should be driven with high efficiency at optimal operating points, which are selected based on their efficiency using an experimental engine test. These operating points are called the optimal operating line (OOL), and the efficiency of the generator should be maximized on the OOL. Therefore, this paper proposes to maximize the efficiency of the generator in the EGS of a PHEV.
Meanwhile, permanent magnet synchronous generators are well-known as suitable candidates in PHEV because of their performance characteristics such as high power density and efficiency. According to PM arrangement, a surface-mounted PM synchronous generator (SPMSG) and an interior PM synchronous generator (IPMSG) are classified. In this paper, both of them have been designed and applied to optimal design to maximize the efficiency on the OOL based on finite-element analysis, where intelligent mesh adaptive direct search was used as the optimization algorithm. The generators were experimentally tested and compared in terms of torque density, efficiency, total harmonic distortion and torque ripple. Since the performance of IPMSG is better than that of SPMSG, it was selected and built into the vehicle. Finally, the IPMSG built-in PHEV has been tested and validated. A full paper will describe the above-mentioned studies in detail. This work is funded by the Korea Automotive Technology Institute.
A novel single phase tubular permanent magnet linear generator for Stirling engines is proposed in this paper. It has a bread type winding, which has no cutting. It comprises an outer-stator, an inner-stator and a mover, and they are mounted in a cylinder. The winding coils are wound in a ring shape and placed in the slot of the outer-stator. The inner-stator is made up of a ferromagnetic ring. The mover is drivingly linked to a piston and it consists of four ring-shaped permanent magnets that are all polarized radially, and the polarized direction of the two permanent magnets on the outside are in the opposite of that of the two magnets on the inside. The stator outer diameter is 80mm and the outer-stator laminated thickness is 22mm. The whole mover laminated thickness and the inner-stator laminated thickness are both 30mm. The inner-airgap is 0.2mm while the outer-airgap is 0.3mm. The silicon steel material of the outer-stator and inner-stator is 50W470. The permanent magnetic part of the mover is made up with Nd-Fe-B, and the non-magnetic support shaft is made up with aluminum. Taking the space of outer-stator’s slot into consideration, the turns of diameter of the copper wire is selected as 71 and the diameter of the copper wire is chosen as 1.5mm when concerned about the output current value is approximately 10A. The three-dimensional finite element model of proposed TPMLG is established. The model and its boundary conditions are presented. Through the FE model, its electromagnetics analysis is carried out. The performance of this generator under reciprocating frequency 75Hz is investigated and analyzed. With the FE model, the weight of the iron core of outer-stator, inner-stator, coils of copper, mover with four permanent magnets and the support shaft are calculated thoroughly. The average power per unit mass is around 115.848W/kg. The advantages of the generator that it has high-power density are shown. It can be used as the generator in the Stirling engine.
Rotational machine is a kind of promising high temperature superconducting (HTS) electrical application. Among them, the coated conductor HTS coils are most commonly used as DC magnets because the DC HTS coils in the rotor under the relatively stationary fundamental magnetic field does not cause AC loss. However, in actual operation, AC loss produced by the harmonic magnetic fields is inevitable. Other inevitable transient electromagnetic disturbances in the operating machine environment can also cause AC loss. Considering cooling penalty, these kinds of AC loss may not be ignored, and it is not easy to be calculated because of the complex electromagnetic environment in actual operating machines, the large scale of HTS coils, high aspect ratio for coated conductors, and the anisotropy property of HTS tapes. This paper introduces and verifies a fully coupled numerical method for coated conductor HTS coils in operating machine based on T-A formulation. This method can calculate the AC losses of HTS coils in the operating machine environment fast and effectively. Using this method, the effects of ferromagnetic stator teeth and shielding layer on AC loss produced by the harmonic magnetic field and load change are also quantitatively displayed.
In this paper, the motor-generator set was developed to test the various output performance of a 1-kW-class high-temperature superconducting generator (HTSG) which is charged by HTS contactless rotary excitation device (CRED). First of all, the various full components for 1-kW-class HTSG were manufactured and assembled including a salient rotor pole with HTS coils, rotating shafts, torque transferring structures, rotating and stationary parts for CRED, and liquid nitrogen cooling system. Then, this assembled machine was connected with induction motor which is driven and controlled by voltage source inverter and three phase resistive and inductive road bank. The rated operating current of HTS field winding can be excited by rotation of HTS strands attached on toroidal rotor head of CRED at rated charging speed. After field winding charging, 1-kW-class HTSG was tested in no-load and electrical load modes to measure output power characteristics.
Acknowledgement: This work was supported in part by the “Human Resources Program in Energy Technology” of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy (MOTIE), and by Korea Electric Power Corporation. (Nos. 20184030202200 and R18XA03)
This paper focuses on the design of a Vernier machine with HTS bulks on Flux Modulation Pole(FMP) and HTS field winding. Vernier machine gained importance in recent years for low-speed and large- torque (LSLT) applications, such as wind power generation. Despite the Low-speed high-torque capability, Vernier machine have lower Power factor than the power factor of conventional HTS Field Winding synchronous machine. The key of improvement is introduction of HTS bulks which decrease the flux leakage on the Flux Modulation Pole. In the analysis, Finite Element Analysis(FEA) was used to obtain the magnetic flux field distribution and the performance of the Vernier machine which is resulted by the magnetic gearing effect of the FMP. The voltage harmonic components of Vernier machine with HTS bulks was also investigated. Based on the design, we investigate the advantage of the HTS field winding Vernier machine with HTS bulks comparing to the one without HTS bulks.
China Southern Power Grid, Ltd. has established a project to study the feasibility of installing large-scale HTS dynamic synchronous condensers in Ultra High Voltage Direct Current (UHVDC) transmission grid. To investigate some key technologies, a small–scale one, such as 300-kvar class HTS synchronous condenser prototype is designed. The electromagnetic and structure design of this prototype is described in this manuscript. The rotor excitation winding, composed of totally 8 double-pancake racetrack coils, are wound by ReBCO coated conductors. It is cooled by forced-flow helium gas, and the working temperature is expected below 30 K. The water-cooled stator winding is embedded in non-ferromagnetic stator teeth. Made by fibre glass epoxy, the torque tubes are optimized to balance the thermal leak and mechanical requirement. The pair of copper (OHFC) current leads are designed to transport current from room temperature to cold terminals which are conduction cooled to below 30 K. All the rotor structures are enclosed in a vacuum chamber. Before assembling, the critical current of the rotor magnets are tested in liquid nitrogen temperature, and the test results shows the satisfactory with the design values.
Wed-Mo-Po3.06-05 [41]: Design and Numerical Analysis of 10 MW-class Fully-Superconducting Synchronous Generators Installing the New Casing Structure for Turboelectric Propulsion System
Nowadays, feasibility study of fully turboelectric propulsion systems for electric aircrafts are being conducted. Fully superconducting rotating machine is one of the solutions to realize fully turboelectric propulsion systems with lightweight and high power density. In our previous studies, we reported the high output power density over 20 kW/kg for the 10-MW-class fully superconducting generators. In the previous model it was assumed that the rotor is installed at the space filled with helium gas and the stator is cooled by sub-cooled liquid nitrogen at 65 K or liquid hydrogen at 20 K. The helium gas is cooled by the inner wall of the stator case. Therefore, the operating temperature for the field windings in the rotor was restricted to the liquid refrigerant temperature. In this study, we studied on the new model where the field winding is installed into another vacuum chamber and independently cooled by the other gas/liquid refrigerant. It composes a rotor. In this case it is possible to make the operating temperature of the field windings different from that for the armature windings. In this paper, various kinds of properties of the fully-superconducting generators with this new structure. The operating temperature of the field winding, Tf-op, are set to 20-65 K as a parameter. The dependences of the Tf-op on the AC loss, efficiency, dry weight, output power density were investigated and compared. In addition, the numerical analysis of the thermal stability was performed.
This paper presents the results of the electromagnetic design and numerical analysis for a 10-MW-Class second generation high-temperature superconducting generator (2G HTSG). Since the offshore wind power has the technical and economic difficulties in a regular maintenance due to geographical conditions that are difficult to access, the operation reliability of 2G HTS coil for the rotor-field poles should be technically guaranteed to realize the feasible application and, by extension, commercialization of the 10-MW-Class HTSG on offshore wind power. In this study, three winding insulation techniques (WITs) for HTS field coils (FC), such as no-insulation, metal insulation, and metal-insulator transition insulation, are considered to give a definite report the operation reliability of the 10-MW-Class HTSG in offshore environment. Using the time-transient solver of the three-dimensional electromagnetic finite element analysis (3-D EM FEA), EM characteristics of HTSG with three WITs are investigated and compared in terms of the performances of HTSG’s electrical output and HTS FC’s critical current. Then, in order to analyze the charging and discharging characteristics in steady-state operation as well as the electrical and thermal characteristics in transient-state operation of HTS FCs with three WITs, electric equivalent circuit models are built with key parameters based on EM FEA result. Finally, the performances of HTS FCs are discussed and evaluated in electromagnetic response time and stability characteristics.
Acknowledgement: This work was supported in part by the 2019 scientific promotion program funded by Jeju National University, and in part by Korea Electric Power Corporation (No. R18XA03)
A unique activation technique for permanent Nd-Fe-B magnets which were embedded in the rotors of interior permanent magnet (IPM) motors has been developed as a magnetizing tool using high temperature superconducting (HTS) bulk magnets. The experimental and numerical simulation studies were conducted to evaluate the magnetic field-trapping performances in two manners of we call “scanning” and “stamping” modes for the rotor of air-conditioner compressor in hybrid-type automobiles. The sample rotor with demagnetized permanent magnet plates were exposed in the intense static magnetic fields above the magnetic pole which contained the bulk magnet generating over 3 T. The magnetization property of permanent magnet plates in the rotor was found to follow the magnetization curve of the material with its anisotropic magnetization property. As a result, the sample magnets were perfectly magnetized in the static magnetic fields. The precise simulation on the flux distribution in the rotor clarified that it is important to make the direction of flux in the hales of rotor core and the easy magnetization axis of PM identical. We convinced this activation technique should enable us to promote the degrees of freedom of motor designing and processing.
Wed-Mo-Po3.07-03 [45]: Measurement and Analysis on Local Magnetization Properties of RE-123 Coated Conductor with DC Transport Current and External Magnetic Field
We study to increase a trapped magnetic field of HTS bulk magnet activated by pulsed field magnetization (PFM). Although various methods to enhance the trapped field are considered, they can be broadly divided into two approaches; one is improvement of magnetizing method and another is modification of exciting equipment. In the latter, a pulse width was expanded by changing an inductance of the coil and a capacitance of condenser which was current source. However, it costs a lot for the modification. In an exciting system of PFM, soft-iron yokes are used in order to expose the bulk to the magnetic field for a long time. It can be predicted that that trapped field is improved because magnetic flux hold in a soft-iron is increased when the size of yoke is increased qualitatively. On the other hand, an effect of the size of soft-iron yoke on trapped field performance has not been evaluated quantitatively. In this paper, a GdBCO bulk 60 mm in diameter and 20 mm thick is magnetized by applying a single pulsed field with varying an amplitude of applied field and temperature when soft-iron yokes of 40, 64 and 80 mm in diameter are used, and these trapped field characteristics are compared. This method is useful for practical use because the trapped field can be enhanced only by changing a soft-iron yoke.
We have studied both theoretically and experimentally the process of magnetization of HTSC square (12mm x12mm) tape as well as stack from tapes by means of small source of magnetic field. The size of magnetic field localization was less than the size of sample. Local magnetic field induced the currents which were calculated in the frame of critical state model taking into account the dependencies of critical current on magnetic induction. The magnetization of the sample was calculated as well. We investigated the various methods of applying of magnetic field in which the amplitude of magnetic field was changed adiabatically. The position of source of local magnetic field changed too. It was shown that multiple cyclic impact of external field leads to increase in total magnetic moment in the sample up to 80 per cent from the maximum theoretical limits for studied sample. The results obtained make it possible to optimize the magnetization regime of a square fragment of a tape (or a stack of tapes) when implementing a magnetic pump on their basis.
The field and field quality was modeled for a DC planar undulator designed to be wound with YBCO coated conductor. The undulator field on axis target was 1.3 T with a period length of 17 mm. The winding former and pole material were 1006 LCS, and the gap was 9.5 mm. A tape wound design was used, with 50 tape layers in a groove. The tape was taken to be 4 mm wide and 0.08 mm thick, with 10 m insulation on all sides (total thickness tape + insulation 0.1 mm). Operational temperature was assumed to be 4.2 K, and a 900 A Ic was assumed. Based on this design, the field, both in the winding, and in the bore, was calculated using FEM modeling in COMSOL Multiphysics software. Particular attention was paid to the bore region, where the field contribution of the shielding currents in the YBCO coated conductors were included. These results were compared to simple estimates based on analytic models. The field contributions were explored for different excitation levels, and for different cycle histories. Cycle histories were developed to minimize the field error contributions of the shielding currents at fields of active interest (user field measurement points). It was seen that a small pre-cycle could reduce both field error and its change with time.
Due to its excellent current-limiting capacity, especially at the initial dc fault transient stage, the analyses of dc inductive superconducting fault current limiter (I-SFCL) are attracting more attention. In this paper, a modelling method for dc I-SFCL was proposed to describe its nonlinear characteristic of inductance. Firstly, the structure of dc I-SFCL was briefly introduced. Then the magnetic field distribution, including the leakage magnetic flied distribution, was considered by finite element method (FEM) to establish an equivalent magnetic circuit of the dc I-SFCL. By analyzing the equivalent magnetic circuit, the relationship between dc transient current and the inductance of dc I-SFCL was calculated. Accordingly, a mathematical I-SFCL model can be built in MATLAB to discuss the current-limiting performance. A dc I-SFCL prototype has been fabricated to verify the accuracy of the proposed modelling method and simulation result.
Abstract: The short-circuit fault current on the DC side affects the operation safety of the multi-terminal flexible HVDC transmission system (MTDC) seriously. At the same time the superconducting fault current limiter (SFCL) has received extensive attention in limiting the DC impact current due to its characteristics such as fast response speed, good current limiting effect and zero impedance at steady state. At present, simulations of the resistance of YBCO tapes under DC impact is relatively larger, which affects the design accuracy of SFCLs. In this paper, the characteristics of DC fault current are studied. The resistance and other parameters of YBCO samples under DC impact are measured by use of a DC impact platform. The heat transfer process of YBCO tapes under DC impact is studied and three different modeling methods are obtained. Finally, these methods are improved considering the characteristics of the fault current limiting magnet (FCLM), and the simulation results are compared with the experimental results of FCLMs. The advantages and disadvantages of three modeling methods are compared, and the correctness is verified. This research aids in simulation analysis and optimization design of DC SFCLs.
In a power system, fault currents are on the rise and are becoming a common problem. Although several methods are used to restrict fault currents, the methods have demerits in respect of stability and reliability of power system. In this regard, high temperature superconducting (HTS) fault current limiting applications are considering as an alternative and a number of related researches are in progress.
The authors suggest a novel inductive type fault current limiting HTS power cable, which takes the form of wound cable with iron core. When fault current traveling through the cable, the HTS shield layer experiences a transition from the superconducting state into a resistive state by the quench. It causes release of magnetic flux generated by the current to the out of shield layer, then the amount of magnetic flux interlinkage for the wound cable increases and inductive impedance also increases. The cable provides two merits, which are no additional insulation for the fault current limiting function and quick recovery time after fault clearance due to very low heat generations on the HTS layers.
In this paper, a novel inductive type fault current limiting HTS power cable was suggested and its effect was described through design and simulation results. The results are discussed in detail.
This work was supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP) and the Ministry of Trade, Industry & Energy(MOTIE) of the Republic of Korea (No. 20171220100400).
Wed-Mo-Po3.08-05 [57]: Simulation and experimental investigation on the critical current and AC losses of a hybrid superconducting fault current limiter with bias magnetic field during normal operation
The level of fault current has been increases quickly with rapid growth of electric load in recent years. The capacity of conventional circuit breaker has been unable to meet the demand. The wide application of high temperature superconducting fault current limiters (HT SFCL) provides a new avenue for power protection. They use the electrical properties of HTS to instantaneously protect power grids which can not only reduce the capacity of the circuit breaker but also improve safety of power grids. This paper deals with a novel hybrid superconducting fault current limiter with bias magnetic field. This high temperature superconducting fault current limiter has a reactor with double-split symmetrical windings and a non-inductive high temperature superconducting (HTS) magnet which is in series to one branch of the reactor. The simulation model of the hybrid SFCL is established in Matlab/Simulink to investigate its performance in a power grid. An experimental system is set up with a unit of SFCL magnet immersed in the liquid nitrogen and a high speed Data Acquisition (DAQ) System of National Instruments (NI) based on LABVIEW. The characteristics of the critical current, AC losses for the non-inductive superconducting unit of SFCL are experimental investigated to verify the effectiveness of the hybrid SFCL and evaluate the technical feasibility.
Recently, high voltage direct current (HVDC) power systems have been widely developed and used around the world because of their large transmission capacity and low power loss. However, conventional DC circuit breaker (DCCB) is difficult to interrupt large fault current. Therefore, to limit the fault current to a relatively low level, a superconducting fault current limiter (SFCL) is introduced to effectively and rapidly limit the fault current due to inherent physical properties of the superconductor and significantly reduce the stress on the DCCB of the HVDC system. This paper presents a conceptual design of a saturated iron core SFCL (SI-SFCL) for a 15 kV, 3 kA DC power system. First, the electrical characteristics of the SI-SFCL were analyzed and the relationship between the fault current and the SI-SFCL parameters was defined. Then, the detailed design process of the SI-SFCL and its corresponding configuration were summarized. A mathematical model was developed to investigate the fault characteristics of the 15 kV, 3 kA DC power system and to determine the parameters of SI-SFCL accordingly. We also implemented the PSCAD/EMTDC simulation to analyze the operation and fault current limiting characteristics of the SI-SFCL. The validity of the fault current limiting performance and the design parameters was verified through the simulation results. When a fault occurred, the iron core was no longer saturated and the inductance of the SI-SFCL was increased due to the increase of permeability. As a result, the inductance of the SI-SFCL became much larger than that of the normal operating state for a very short time during the fault, limiting the fault current up to 70%. Since the SI-SFCL was not quenched, the system was immediately recovered by reclosing of the DCCB. The results of this study will be effectively applied to the development of SI-SFCL for large-scale HVDC power systems.
Fault current limiter (FCL) is commonly applied as a current-limiting device to improve the stability of the power system. In this paper, a Flux-coupling type Superconducting FCL (FC-SFCL) with a pair of HTS parallel windings has been developed. The limiter is based on disconnecting coupling windings for current-limiting, which has a low steady impedance at normal state and higher limiting one after fault. The problem of ac losses is fierce, which affects the thermal stability for larger leakage flux and greater fau