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In this paper, we present the fabrication and performance of a linear-motor type flux pump with a pumped current larger than 640 A. This high-temperature superconducting (HTS) flux pump can be used for magnetic resonance imaging (MRI) magnets and HTS electric machines. We use the flux pump to charge 10 superconducting closed-loops, and show the tested results of pumping current under different applied frequencies and magnetic field amplitudes. This flux pump device can output direct current larger than 640 A at 77 K. The output of this flux pump equals to a DC power source with low output voltage and high output current. Comparing with the traditional power supply of the same rated current, the size of this HTS flux pump is much smaller, while it also eliminates the harmful metal current leads that cause heat leakage. We show that, by increasing the length of the travelling wave region of this flux pump, there is no limit to the output of the current output, which can reasonably reach the kilo-ampere level. The purpose of this paper is to test the reliability of the methodology for the large current HTS flux pump.

This paper presents a solution for the regulation of electric field along the post insulator of 1 MV DC GIL for ITER neutral beam injector (NBI). To regulate the electric field distribution, a simulation model of the post insulator with surface nonlinear conductivity is developed. The actual working conditions of NBI GIL including a square wave voltage, a radiation environment as well as surface charge accumulation are considered. The results show that radiation will lead to a significant increase in the conductivity of SF6 gas, which makes the heteropolar charges from the SF6 gas domain dominate the surface charge. The tangential electric field on the insulator surface is seriously distorted by heteropolar charges. The post insulator with the design of surface nonlinear conductivity can effectively dissipate the surface charge and the tangential electric field along the insulator surface can be reduced by up to 46.5%. This paper aims to propose research methods and feasible means for the reasonable insulation design of NTER GIL to ensure the safe and stable operation of ITER.

An HTS flux pump is an effective device to compensate the field decay in HTS magnets running in persistent mode. This paper contains updates to the model for the travelling wave HTS electromagnetic flux pump, in which the magnetization system is modelled as an L-R circuit. In this paper we consider the various sources of resistance. There are three components, joint resistance, resistance of superconductor and dynamic resistance. Joint resistance is treated as a constant. The superconducting resistance is derived from the E-J model and finally the dynamic resistance is a function of applied field strength and frequency. In addition the model includes the electromotive force which is a function of the applied field, frequency and surface area of the tape. This is a calculated value based on the φ model we built. In order to test the model, a series of experiments were performed in which an HTS coil was actuated using our flux pump. The flux pump test rig was made from 4-pair rectangular copper solenoids with laminated iron cores, which were fixed on the supporting iron frame. This rig was used to magnetize a double layer HTS racetrack coil at 77 K. The induced current in superconducting coil can reach more than 90% of critical current. Our model was found to be a good fit to the experimental data.

The paper explores the idea of reducing the amount of REBCO conductor in Resistive Superconducting Fault Current Limiters (R-SCFCL) by reducing the temperature of liquid Nitrogen from 77 K to 66 K. Because of lower temperature, the critical current increase approximately two times, and instead of two parallel tapes, one can use only one tape in a 1000 A class R-SCFCL. However, recent experimental results on short samples show a frequent degradation of superconductors by DC current limitation at 66 K. The paper reports our investigation of this phenomenon by experiments complemented by extensive numerical modeling. We suggest that the primary cause of conductor degradation initially appearing at 66 K should be sought in the first sub-millisecond period of the limitation pulse. We observed that a reduced initial rate of the current rise during the limitation event can prevent the conductor damage.

This paper proposes an approach to account for a fast electromagnetic quench propagation among electromagnetically coupled no-insulation (NI) high temperature superconductor (HTS) coils. Recently, multiple groups have reported that the conventional lumped-circuit model, which has well demonstrated charging and discharging behaviors of an NI magnet, could not account for post-quench behaviors. Specifically, terminal voltages of individual pancake coils were estimated to be too high than the simulated ones. This paper proposes an approach that focuses on the post-quench simulation of an NI HTS magnet. To explain this phenomenon as a lumped circuit, a new approach was introduced. The key idea is inversely calculating key parameters of the lumped circuit that best demonstrates the non-linear post-quench behaviors. After defining the necessary assumptions, we adopted inverse-calculating methods to analyze the test results of high field NI HTS magnets. Simulation results suggest that after a quench, the index resistance changes in a different way from the previous theory, while the change in characteristic resistance is similar to conventional theory.

This paper presents numerical studies on the mechanical behavior of dry-wound high-temperature superconducting (HTS) racetrack coil. After calculating the Lorentz force induced from the self-field of the racetrack coil based on the 3D finite element method (FEM), the 2D mechanical stress analysis is performed based on the plane-stress assumptions to mitigate computational loads, and the mechanical behavior including displacement and stress are investigated. Based on analysis model, two following case studies are conducted: 1) analysis of mechanical behavior on various-shaped of racetrack coils having a different ratio of straight section length and semicircular section radius, and 2) analysis of stress reduction effect according to the degree of curvature when slight curvature is included in the straight section. In each case study, the factors affecting the mechanical behavior of racetrack coils are numerically analyzed and their trends are presented. The results obtained in this paper would be useful for the design of dry-wound racetrack coil, including no-insulation coil, applied in a large-scale and high-field application.

This paper discusses the simulated and experimentally observed quench behavior of the first HL-LHC Twin Aperture Orbit Corrector Prototype, also known as the MCBRDp1 magnet. This superconducting magnet features two independently powered apertures. Each aperture comprises two concentric canted-cosine-theta-type Nb-Ti/Cu coils that together generate a dipolar magnetic field over the bore. These coils are held in place by conductive aluminum-alloy formers. The circuit is protected by a combination of energy extraction and quench-back in the coils. When the coils are discharged over an energy extractor, eddy currents are generated in the formers, and the resulting heat quickly and efficiently brings the Nb-Ti/Cu strands above their current sharing temperature, provided that the resistive voltage over the energy extractor is sufficiently large. This paper compares simulations and experimental observations. It is shown that with the BBQ tool, the initial voltage development after a training quench is correctly reproduced. The ProteCCT simulation tool is shown to be consistent with experimentally observed discharges of the MCBRDp1 prototype for different bath temperatures, energy extractor types, and initial operating currents. The baseline energy extractor resistor value of 1.5 Ω and the non-linear varistor option both give worst-case hotspot temperatures below the 200 K hotspot temperature limit. At ultimate current, the resulting hotspot temperatures are 143 and 167 K, and the peak voltages-to-ground are 590 and 440 V, respectively.

High-temperature superconducting (HTS) flux pump can supply DC current into the superconducting magnet coil in a contactless manner. The flux pump works similarly as a DC power supply, with low output voltage and high output current. In this paper, based on the linear-motor type flux pump previously introduced from our laboratory (W. Wang et al. 2018), we miniaturized it and measured its the output DC voltage. By using different peak values and frequencies of the applied AC travelling magnetic wave, we obtained the pumping characteristics of this linear-motor type flux pump. With the same applied magnetic strength, it was found that the pumped current is not directly proportional to the frequency, we interpret that the critical current of the HTS stator was likely deteriorated by the heat generated in the stator due to high magnetic field amplitude and frequency. From the pumping current curve, a voltage-current relationship of the HTS flux pump was obtained. This method mentioned in this paper can directly derive the output voltage of the HTS flux pump, and could also be applicable for all other types of flux pumps. The method helps further optimizing HTS flux pumps which will be applied in the dedicated MRI and the brushless superconducting motor under developing.

Magnetic bearings composed of multiple basic cubic superconducting bulks were investigated. This paper aimed to integrate multiple basic cubic bulks with different performance characteristics and to control the magnetic field properties through design of their arrangement. If this magnetic field characteristic can be controlled, then the optimum configuration for a magnetic bearing can be deduced. In this paper, we aimed to control magnetic bearings with a plurality of basic unit cubic bulks and to control variations in the magnetic characteristics of the bearing surfaces via the arrangement design. We performed calculations of the optimum arrangement that minimizes the inclination angle of the rotation axis of the floating rotating body by combining the structural arrangement pattern of the bearing surface. We constructed a model with a three-row, three-column square arrangement and calculated the layout pattern via an optimization calculation. The cubic bulk was then constructed with this arrangement pattern, and the inclination of the axis of rotation of the floating body was measured using a laser sensor and compared with the calculation result. In addition, the distance between the bearing surface and floating body and the levitation force were measured. We confirmed that suppressing the inclination of the rotation angle through the optimum arrangement was highly effective, indicating the feasibility of controlling the levitation force.

This paper presents the power dissipation analysis on high-temperature superconducting (HTS) coated conductor tapes and coils under the action of various oscillating currents and fields. The loss calculation on HTS coil was carried out by the H -formulation model implemented in the finite-element method (FEM) software package COMSOL Multiphysics. There were four different oscillating (ac) signals in this paper: sine, triangle, sawtooth, and square. Two scenarios causing loss in HTS tapes and coils which have been analyzed: Scenario 1 ac transport current; Scenario 2 ac magnetic field. The simulation results were compared to the experiment results with the typical sinusoidal ac signal.

High-temperature superconducting (HTS) soldered-stacked-square (3S) wire has been proposed as a novel potential structure for the second generation HTS wire. Twisted method is an available way to decrease the anisotropy and improve the performance of 3S wire in high field application. This paper presents a three-dimensional numerical model based on H-formulation for the 3S-twisted (3S-T) wire. AC loss is evaluated as an important parameter when 3S-T wire is applied in alternating current or magnetic field circumstances. Three different structures of 3S-T wires are considered, and the validity of the general model is verified by the corresponding experimental results. The results show that there is no significant eddy loss existing in the 3S-T wire. Moreover, if more HTS tapes are contained in 3S-T wires, the current distribution will be closer to elliptical shape and the current phase in different YBCO layers will be changed. The transport AC loss can be slightly reduced through the twisted method. The work in this paper will be helpful to understand the electromagnetic characteristics of 3S-T wire.

Flux pumps provide a contact-free method of energizing dc currents in superconducting coils. Since a predictive quantitative theory for dynamo-type flux pumps does not exist yet, the optimization of device designs must proceed through empirical experiment. In this paper, we investigate the effect of varying the annular width of the iron stator yoke within a high-temperature superconducting dynamo. Reducing the dimensions of this iron yoke reduces the mass of cold iron within the dynamo, and hence has advantages in terms of weight, cryogenic efficiency, and eddy current losses. In this paper, we have investigated the dc output from an experimental high-temperature superconductor (HTS) dynamo in which the annular width of the iron yoke Δ r is varied across a factor of four. Varying this dimension affects the reluctance of the magnetic circuit formed between the rotor and stator. We have shown that the dynamo output is surprisingly insensitive to the size of the iron yoke. The maximum current output ( I sc) is independent of Δ r at all flux gaps. At the closest magnet–stator flux gap, a fourfold increase in Δ r results in only a ∼30% increase in the open circuit voltage ( V oc) and internal resistance ( R d) of the dynamo. Our results indicate that the smallest yoke studied (Δ r = 6 mm) can be utilized with a 25.4-mm Nd-Fe-B rotor magnet, without adverse impact on the electrical performance of this type of HTS dynamo.

© 2017 IEEE. High-Tc superconducting (HTS)-coated conductors are a promising option for the next-generation power devices. However, their thin-film geometry incurs dynamic loss when exposed to a perpendicular external ac magnetic field, which is difficult to predicate and estimate. In this paper, we propose and verify a numerical simulation model to predict the dynamic loss in HTS-thin-coated conductors by taking into account their Jc-B dependence and I-V characteristics. The model has been tested on a SuperPower YBCO-coated conductor, and we observed a linear increase of dynamic loss along the increasing field amplitude after the threshold field. Our simulation results agree closely with experimental measurements as well as an analytical model. Furthermore, the model can predict the nonlinear increase of dynamic loss at high current, while the analytical model deviates from the measurement results and still shows a linear correlation between the dynamic loss and the external magnetic field. In addition, we have used this model to simulate the distributions of magnetic field and current density when dynamic loss occurs. Results clearly show the flux traversing the coated conductor, which causes dynamic loss. These distributions have also been used to analyze the change of dynamic loss when either the transport current or the magnetic field increase individually, while the other factor remains constant. The simulation analysis on dynamic loss is done for the first time in this paper, and our results clearly demonstrate how dynamic loss changes as well as its dependence on transport current and magnetic field. © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

This paper presents an axial-flux microelectromechanical systems micromotor with dual-rotor and 10 mm diameter. The leakage fluxes are a large proportion of the total flux due to the micro dimension. Therefore, an accuracy prediction of the boundaries of leakage fluxes is vital for motor design. Response surface methodology is well adapted to obtain empirical formulas of the boundaries of the leakage fluxes in this paper. Additionally, an improved pigeon-inspired optimization algorithm is used to efficiently search the coefficients of the second-order empirical formulas. The feasibility of the proposed method is validated by the three-dimensional finite element analysis. Finally, the method is applied to accurate design one micromotor.

Gapped iron-core reactors can obtain larger inductance, but they make larger vibration and noise than other kinds of reactors. On vibration dampers, many researchers kept their eyes on vibration isolation structures or vibration isolation materials. However, they did not compute reactor core vibration under fundamental frequency voltage or harmonic one. Because stress is the inherent reason of vibration and noise, this paper proposes a finite-element model for reactor core stress calculation based on the Maxwell stress theory. The model can handle reactor exciting currents, not only fundamental frequency but also superposition of fundamental frequency with different harmonics. Because core materials have different magnetic characteristics under different excitation conditions, this paper tested multigroup H-B curves to support the simulation. Then, the finite-element method is used to calculate the magnetic field and Maxwell stress distribution. Finally, the frequency spectrum of the stress is analyzed to provide a theory basis for further analysis of vibration and noise reduction in gapped iron-core reactors.

This paper extends the previous effort by Gosselin and Bejan to optimize an electromagnet according to the constructal design approach. This paper pursues two objectives in the solenoid design: a constant Fabry factor of 0.16 and a minimum hot-spot temperature in the coil. In order to minimize the hot-spot temperature, cooling discs made of high thermal conductivity materials are inserted to transport heat to disc surfaces fixed at constant temperature (heat sink). Subsequently, two cooling disc configurations are investigated in this paper: discs with heat sinks on the outer surface and on both the inner and outer surfaces. A mathematical model for each configuration is presented and numerically verified using a commercial FEA software. These models are then used to examine the hot-spot temperature variation with respect to the number of cooling discs. In addition, optimal solenoid radius and length, as well as cooling disc volume, are determined for a range of fixed solenoid volumes; thereby, the ideal solenoid volume resulting in the minimum hot-spot temperature is found. In summary, the qualitative trend of the tradeoff between heat transfer and electromagnetic performances are analyzed, and the optimal design is deduced for the maximum performance from a combined standpoint.

This paper deals with the effect of magnetic flux diverters on the current decay behaviors of high-temperature superconducting (HTS) coils which operate in semipersistent current mode (PCM) under alternating magnetic field. In superconducting synchronous machines, the HTS field coil can be designed to operate in PCM to obtain a steady magnetic field during operation. Due to the alternating magnetic field from the armature winding, the HTS field winding experiences an external magnetic field. As a result, the additional magnetization ac loss in the field coil would be induced, and it affects the current decay characteristics. In order to improve the current decay behavior of the HTS field coil, the use of flux diverter made of magnetic material can be considered. In this paper, we experimentally investigated the current decay characteristics of HTS field coils with magnetic flux diverters under alternating magnetic field. The measurement setup, which is composed of HTS field coil and armature coil, was fabricated. The measurement test of the current decay on the HTS field coil in PCM operation was carried out as functions of the amplitude and frequency of the armature coil.

The design considerations of permanent-magnet transverse flux machines (PMTFMs) with soft magnetic composite (SMC) cores are investigated in this paper. A simplified torque equation of the PMTFMs is deduced first. It is shown that the torque coefficient is directly related to the air-gap flux density, the number of pole pairs, and the stator slot width, etc. To accurately illustrate the influences of these parameters on motor performance, electromagnetic and mechanical analyses are completed by using the 3-D finite element method. For the laboratory prototype, SMC cores can be manufactured by two methods, namely, wire cutting and mould pressing. It is found that wire cutting method deteriorates the magnetic properties of SMC cores and lowers the machine performance. The performance predictions of the PMTFMs are compared for these two methods in this paper. The calculation results are verified by the experimental results.

In this paper, the levitation force measurements have been carried out by the magnetic force measurement system under both field-cooling and zero-field-cooling regimes, whereas the magnetic field distribution over the permanent-magnet guideway (PMG) was calculated by numerical analysis based on the finite-element method. It was shown in this study that the vertical levitation capability and stability of Maglev systems can be improved depending on the cooling regime, pole number, and suitable arrangement of the PMG. In this paper, it was shown that when the pole number increases, the levitation force density increases. It also appeared that the reasonable position of the supplementary permanent magnet and appropriate cooling heights are key parameters for both levitation performance and stabilization of the high-temperature superconductor (HTS) Maglev. It is believed that the numerical and experimental data in this paper are useful for relative design and practical application of HTS Maglev systems. © 2015 IEEE.

In this paper, we constructed test equipment for a rotating machine that uses a superconducting bulk rotor and performed a rotation test. When a superconducting bulk rotor is used, a fluctuating magnetic field generates ac loss, it is possible to decrease its trapped magnetic flux. Performance of the rotating machine under test was influenced by the ac loss generated by a fluctuating ac magnetic field. We modeled the motor used in this paper on an axial-type synchronous motor, where the magnetic field generated by the stator coils causes the rotor to rotate. We then measured the influence of the stator coils on the superconducting bulk rotor. First, we confirmed that the temperature of the bulk rotor modules was properly controlled and could generate a trapped magnetic flux equal to that during zero-field-cooled magnetization. A technique for magnetizing two or more bulks concurrently was used. Next, we performed the rotation test at low speed. The maximum rotational speed during the test was 300 r/min. The operation time at a steady-state speed was 600 s. The maximum value of the generated magnetic field of the stator coils was 50 mT. Finally, we confirmed that a shielding ring made of superconducting wire decreased the influence of a fluctuating magnetic field.

This paper proposes a millisecond-scale electromagnetic levitator using high-temperature superconducting (HTS) coils. The proposed apparatus consists of an AC power supply, short-circuit switches, an aluminum plate, and two HTS coils. The HTS coils are wound in opposite directions and electrically connected in parallel. Thus, in a symmetric current distribution, the magnetic fluxes generated by the two HTS coils ideally cancel each other. However, in a sudden asymmetric current distribution created by the short-circuit switches, the magnetic fluxes are not cancelled, and the effective magnetic flux induces an eddy current in the aluminum plate placed above the HTS coils. The magnetic flux generated by the eddy current in the aluminum plate and the effective magnetic flux generated by the HTS coils together generate the repulsive force to levitate the aluminum plate. In this paper, numerical calculations and experimental verification of the repulsive force are performed. We show that this apparatus is able to provide a levitation force that we expect will be helpful for devices that need fast switching behavior of the levitation force.

This paper proposes a numerical approach to calculate the characteristic resistance (Rc) of partial-insulation (PI) and no-insulation (NI) high-temperature superconductor pancake coils with the nonuniform current path in such coils taken into consideration. Recently, an analytic approach has been proposed to estimate (Rc) of an NI coil, where the coil current is assumed to be “uniform” over the entire coil. This model, however, is not effective to explain the increase of (Rc) when a coil is modified from NI to PI. In this paper, we first introduce our numerical approach based on a finite element analysis. Then, the charging characteristics of selected PI and NI coils that we had previously reported are analyzed by the proposed approach. Reasonable agreement between the measured and calculated data validates the proposed approach to estimate (Rc) of a PI as well as an NI coil.

This paper presents numerical analysis of the thermally actuated superconducting flux pump. Visualization of the behavior of the magnetic flux helps our understanding of flux injection mechanism. In addition, in order to confirm validity of the result, we conducted a preliminary flux pump experiment. This result qualitatively agrees well with the experimental one. The flux pump system utilizes a particular behavior that permeability of some materials such as Gadolinium is sensitive to the temperature. In this paper a simple heater is used to control the flux pump system.

This paper describes how a passive quench protection system can be applied to long superconducting solenoid magnets. When a solenoid coil is long compared to its thickness, the magnet quench process will be dominated by the time needed for quench propagation along the magnet length. Quench-back will permit a long magnet to quench more rapidly in a passive way. Quench-back from a conductive (low resistivity) mandrel is essential for spreading the quench along the length of a magnet. The mandrel must be inductively coupled to the magnet circuit that is being quenched. Current induced in the mandrel by di/dt in the magnet produces heat in the mandrel, which in turn causes the superconducting coil wound on the mandrel to quench. Sub-division is often employed to reduce the voltages to ground within the coil. This paper explores when it is possible for quench-back to be employed for passive quench protection. The role of sub-division of the coil is discussed for long magnets.

The paper refines the lumped network technique for computation the coupling AC losses and magnetically induced supercoupling currents in multistage cable-in-conduit conductors (CICC) used in superconducting magnetic energy storages, tokamak reactors, etc. Surfaces of the subcables in CICC are not ldquosmoothrdquo, but ldquocorrugatedrdquo. As a result, the contacts between the subcables are featured with a certain periodicity, which depends on the pitches of the sequential cabling stages. The paper presents the expression for such a periodicity and the results of computation of AC loss and supercoupling currents with and without taking into account the envisaged periodicity of the contacts between subcables in multistage CICC, showing the significance of the effect.

This paper describes the passive quench protection system selected for the muon ionization cooling experiment (MICE) cooling channel coupling magnet. The MICE coupling magnet will employ two methods of quench protection simultaneously. The most important method of quench protection in the coupling magnet is the subdivision of the coil. Cold diodes and resistors are put across the subdivisions to reduce both the voltage to ground and the hot-spot temperature. The second method of quench protection is quench-back from the mandrel, which speeds up the spread of the normal region within the coils. Combining quench back with coil subdivision will reduce the hot spot temperature further. This paper explores the effect on the quench process of the number of coil sub-divisions, the quench propagation velocity within the magnet, and the shunt resistance.

This paper compares numerical simulations and measurements of the nonlinear magnetic diffusion phenomenon in a Bi2212 high temperature superconducting (HTS) hollow cylinder. Although the measurements were done many years ago, it is only recently that computer power has become sufficient to reproduce the experiment by simulation on a personal computer in a reasonable time. Observations of flux density (magnitude and phase) both inside and outside the cylinder were carried out at different frequencies and magnitudes of a sinusoidal applied field. In addition, the computed current and flux density profiles inside the superconductor were obtained. The superconductor was modeled by E - J characteristics that depend on Jc and a power law exponent n. Both parameters are isotropic functions of B. The paper shows that numerical methods are useful to extract model parameters and to predict the behavior of HTS elements entering in the conception of real applications, such as the inductive fault current limiters.

The MECO detector magnet produces magnetic fields decreasing from 5 T to 1 T over a curvilinear volume with an axial length of about 26 m using a set of 96 NbTi solenoid coils distributed in 4 cryostats operating at about 4.5 K. At the high field end of the magnet, the solenoids have an inner radius of 0.88 m, and radial builds up to 0.125 m. In these relatively large radial build coils, quenches initiating at the high field region at the inner radius result in warm temperatures at the inner radial region while the outer radial region can remain substantially cooler, even after 60-70 s after most of the current has decayed from the quench-protective dump. Axial and radial tensions can develop in the turn-to-turn insulation from these temperature gradients. This paper discusses the quench modeling process, including the 3-D quench code that provides element temperature vs. time data to ANSYS for analysis of the coil stress. The paper evaluates methods of managing insulation surface-normal tensile stress, including use of copper sheets in single and multiple coils to distribute the transient energy by eddy currents and thermal conduction, which helps minimize temperature gradients in the winding pack. Hard-way winding with ID and OD copper sheets in multiple coils gives the best performance based on both finite element analysis and temperature contour plots

A prevalent room-temperature magnetic refrigerator of permanent magnets usually utilize the structure of stationary magnetic circuit. A new notional method of dynamic-link magnetic circuit (DLMC) is proposed in this paper. The DLMC is made up of a changeable magnetic circuit, and it may generate a time-varying magnetic field in a certain space when some parts of the DLMC move. A typical DLMC is introduced in the paper, and a numerical value calculation and an experiment measuring for the DLMC are presented then. The research result shows that such a DLMC may produce a large variation of magnetic field when it is used in a rotary magnetic refrigerator. Although the minimum field is not equal to zero strictly, but it is much smaller than the maximum field, and the time-varying magnetic fields may be used to magnetize and demagnetize the magnetic refrigerants

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

This article is to study the ramping loss of no-insulation (NI) high temperature superconducting (HTS) racetrack coil under different external magnetic fields during the charging process. An improved equivalent circuit electromagnetic coupling model for the HTS racetrack coil is introduced with good computational speed and accuracy. The simulation results show that the turn-to-turn loss and the change of the lowest critical current position are obviously influenced by the external field that have not been mentioned from our knowledge base. During the rising time of the power supply current, there is little difference in current distribution under different external fields. But after that, steady state of charging process is deeply influenced by the external field. A larger external field will lead to a lower charging current and the external bypass phenomenon. Another result is that the relationship between direction of external field and orientation of coils will influence the lowest critical current amount and position. The relationship between turn-to-turn resistivity of co-winding materials and ramping loss is also discussed in the paper. The distributed unevenness and value of the turn-to-turn loss change with the increase of turn-to-turn resistivity.

Superfluid helium has been used for cooling superconducting magnets in nuclear fusion and high energy physics. This paper presents a simplified final stage process of 1.8 K superfluid helium cryogenic system and its key component sub-atmospheric heat exchanger. Influence of variable thermal parameters of sub-atmospheric heat exchanger on the system performance is studied. The application of sub-atmospheric heat exchanger can increase refrigerating capacity by 61.34% under given conditions. The helically finned-tube heat exchanger (HFHE) is selected, and three-dimensional steady-state numerical simulations of flow and heat transfer performance have been carried out. Nu and f of tube side are 4.5-6 times higher and 95-97% lower than those of shell side, respectively. It is found that HFHE with low fin height and HFHE with filler (nylon rope) have better comprehensive heat transfer and flow performance, and PEC can reach 1.65 and 1.41 respectively under given conditions.

Asymmetric three-pole magnetic bearings (MBs) have higher power density and lower cost, compared to the symmetrical magnetic bearings with four poles or eight poles. This paper presents a new asymmetric three-pole structure with secondary air-gap for a radial magnetic bearing. Asymmetric permanent magnet (PM) biased MB can produce a static levitation force by bias magnetic flux. The secondary air-gap can ensure that the armature winding flux and PM flux are separated. The configures of the proposed MB are demonstrated. Analytical model with equivalent magnetic circuit method is deduced. The design method based on asymmetry factor is proposed for the three-pole MB (TPMB). The characteristics of the TPMB such as magnetic flux distribution and magnetic levitation force are analyzed by the finite-element method (FEM). The design values and FEM results are compared to validate the effectiveness of the presented design method.

In this paper, a novel permanent magnet toroidal motor (PMTM) for hybrid electric vehicles (HEVs) is proposed. According to the structural features and working principle of PMTM, the characteristics of function integration are analyzed from two turning direction combinations of permanent magnetic teeth and windings respectively. The opposite turning direction combination is selected to ensure the uniform rotation of planets. The output speed of planet carrier rotor is deduced, and the influences of worm inner rotor permanent magnetic tooth number and stator pole-pair number on output speed are investigated. Based on the equivalent magnetic charge method, the output torque of PMTM is derived in two driving modes, and the effect of rise angle of worm inner rotor permanent magnetic tooth and toroidal stator winding on output torque are discussed. The research results indicate that the output torque is better with the rise angle αi = 50° and αi ’ = 52°.

Conductor on round core (CORC) cables wound by high-temperature superconducting (HTS) tapes have received much attention due to the advantages in power capacity and mechanical flexibility. This paper first developed a 3D model for a CORC cable through the finite-element method (FEM). Next, the total AC loss caused by transported current only was investigated, revealing the eddy current loss in the tube former contributes to the cable loss. The numerical CORC model was validated by published measurements. Moreover, the AC loss that resulted from a simultaneous presence of transport current and magnetic field was explored. With the induced current, the magnetisation loss generated in superconductors can increase the total loss. It is concluded that the addition of a magnetic field can result in a surge in the total loss of a current-carrying cable.

The objective of the paper is to study the dynamic characteristics of a repulsion mechanism applied in superconducting fault current limiter (SFCL). A novel fully coupled simulation was established, which involved modules of the flexible-body dynamics, the external circuits, motion equations, multi-body dynamics, transient electromagnetic fields and fatigue analysis. The dynamic characteristics including the velocity, the displacement curve, discharging current, Lorentz force, the stress and strain of each dynamic transmission part in the opening process, was calculated. The vulnerable parts were focused and their fatigue life was calculated. The deviation about discharging current and displacement curve of the fully-coupled simulation was experimentally validated to be less than 8%. Stress concentration positions of the vulnerable parts recommended by the simulation results are the same as fatigue failure positions in the experimental results, which verified the accuracy of the fully coupled simulation.

The magnetic property measurementfor grain oriented (GO) silicon steel sheet under non-sinusoidal excitations (DC bias and harmonic) were conducted based on the experimental platform. Based on the Preisach model, the static hysteresis and loss properties were accurately simulated. Furthermore, an improved loss model was proposed by adjusting the statistical parameter of abnormal loss, which depends on the characteristic quantities of DC bias or harmonic excitations. The simulated dynamic hysteresis loops and iron losses under different non-sinusoidal conditions were compared with the measured ones, and thus the accuracy and generality of the improved model proposed in this paper were verified. In addition, the influences of the harmonic and DC-biasing quantities upon the total losses is investigated.

This paper studies the contact bounce during the closing process of a repulsion mechanism applied in a superconductivity direct-current vacuum circuit breaker. A multi-physics field coupling simulation model is established to describe the whole closing process for the repulsion mechanism. The relationship between the V1 and Dmax is obtained for the repulsion mechanism, where the V1 is an instantaneous closing velocity for the movable contact just mating with the stationary contact at the first time, and the Dmax is the maximum contact bounce distance. According to this relationship, the critical instantaneous closing velocity Vcri for the case of no contact bounce is determined. According to Vcri , a novel oil buffer is designed to adjust the closing displacement of the repulsion mechanism to realize a nonclosing bounce. A prototype repulsion mechanism with an oil damper is developed. Its closing characteristics are tested and compared with the simulation results to verify the absence of a contact bounce.

In this paper, an approach for minimizing stress concentration by optimizing the cross section of a toroidal magnet to D-type is presented. To attempt, the magnetic field distributions of both toroidal and D-shaped toroidal magnets were evaluated and compared using the finite element method (FEM), and a convergence curve of maximal magnetic field effect on the winding part was established. We also reproduced an optimal scheme of the ‘D-type' toroidal HTS magnet for a 400 MJ grade SMES based on this convergence curve, and evaluated the distribution of electromagnetic stress in the winding of the magnet, including von-mise stress and hoop stress. We next constructed a reinforcement structure for the ‘D-type' toroidal HTS magnet and investigated the effect of the reinforcement structure material on the suppression of the stress inside the magnet. According these results, an industrialized scheme on the stress inhibition for the D-type HTS magnet for 400 MJ grade SMES was summarized.

The tube structure is an important guarantee for the dynamic stability of the high temperature superconducting maglev-evacuated tube transport (HTS Maglev-ETT) system, it is necessary to conduct relevant research on it. Based on simulation calculations with the FLUENT software, this paper studied the influences of different tube section forms on the aerodynamic drag of maglev train in tube, as well as the pressure distribution in the tube system. In addition, the effects of the setting of cross aisle on the aerodynamic drag of maglev train and pressure fluctuation of flow field in tube were also studied. It was found that the difference in the section forms of tube has little effect on the aerodynamic drag of maglev train and pressure distribution of the tube system under low pressure; the setting of cross aisle can be helpful to reduce the aerodynamic drag of maglev train and the pressure fluctuation around the train to a certain extent. Therefore, the design of cross aisle is recommended for the HTS Maglev-ETT system.

Transverse-flux structure is a potential choice for switched reluctance linear machines (SRLMs) to enhance electromagnetic thrust density. A transverse-flux single-phase SRLM combined with tubular shape, which is a tubular SRLM (TSRLM), is proposed in this paper. There are four stator poles on the cross section of its stator for increasing effective flux path and maximizing flux linkage. To increase the advantage of this novel TSRLM in thrust density, the sensitivity relationships between the maximum electromagnetic thrust value and some key structure parameters are investigated via three-dimension finite element method (3-D FEM). The optimal structural dimensions of proposed TSRLM are determined finally according to a series of sensitivity analysis results. In addition, a new concentrated winding structure is applied in the proposed TSRLM. The analysis result demonstrates that the proposed TSRLM with new concentrated winding structure is superior in thrust density than before.

Magnetic stress is of particular concern for ultra high field magnets, especially, peak hoop stress of those magnets may be locally concentrated by the screening current stress (SCS). For instance, the Little Big Coil (LBC), which was designed, constructed, and operated by a collborate team led by NHMFL, generated the world record magnetic field of 45.5 T, but the conductor in LBC experienced plastic deformation due to excessive SCS. In this paper, to further analyze details of the mechanical stress behavior of LBC magnet, the effect of friction coefficient and overband radial build on stress alleviation is investigated by the parametric study. First, total current density with screening current is calculated by using the $H$ -formulation together with domain homogenization method. Later, the entire magnet structure is modeled by the 2D finite element method to represent preload and axial interactions between each adjacent single pancake (SP), and 3 turns are assumed to be one engineering turn with frictionless radial turn-to-turn contact. While, friction acts between the coil and spacer in a direction that limits the radial displacement. Finally, we discuss the effects of friction coefficient and overband thickness by sweeping those parameters. Our parametric study implies that both friction and overband radial build can reduce peak hoop stress levels of LBC, however, effect of friction is dominant when overbanding is thicker than 0.5 mm.

This paper reports on the integration of publicly available HTS conductor electromagnetic performance data into a magnetic Finite Element model for determining the critical current distribution along a section of conductor in a spatially fluctuating magnetic field. The simulation results from this model are shown to be in close agreement to experimentally obtained results. Typically monitoring for quench is done by measuring the volt-drop along a section of conductor to be protected and determining when the volt-drop reaches a predetermined level. This work shows that under spatially varying magnetic field conditions, small areas of the voltage monitored section of conductor could have already surpassed the critical current level for that section of conductor and hence stand a high probability of being a site for quench. Under these conditions, it is proposed to use the maximum electric field developed along the conductor as a criterion for determining the critical current. This work points to the need for developing a quench detection technique that can be applied to much smaller sections of conductor, particularly in geometries that are expected to experience the largest variations of magnetic field such as that in a rotating electric machine.

Dynamic electromagnetic characteristics is significant for the design and operation of superconducting (SC) electrodynamic suspension (EDS) train. This paper established a three-dimensional transient numerical model in COMSOL. The current density excitation comes from the homogenized model of the superconducting magnet. In order to decrease the computing time, periodic boundary is introduced taking the place of finitely long route. Mapping operator is adopted to ensure the continuity of physical quantities in the case of geometric discontinuity in the process of motion. Induced current and magnetic force at different operation velocity and different structure are simulated. In general, this model could be applied to simulate long term operation. It is also suited for the simulation of propulsion systems for EDS systems. In addition, this model provides electromagnetic environment intuitively that would be helpful for the stability analysis and design of onboard SC magnets during long term operation.

This paper analyses the current distribution in no-insulation (NI) coils in a layer-wound configuration. The investigation aims at comparing the electrical characteristic of two coils wound from the same BSCCO tape, with or without electrical insulation between turns. Both coils are characterized by a very similar geometry, with the same number of turns and layers. Both coils, cooled in liquid nitrogen bath, are charged until the tape critical current is exceeded. To interpret the measurements and analyze the current distribution within the winding, a lumped-parameter equivalent electrical circuit is developed and solved numerically in a time-varying regime. The model results are compared with the signals acquired through voltage taps soldered at the same locations in both coils. Finally, the model is applied to investigate the impact of the transverse contact resistance and to estimate the most stressed locations of the coil during charging, in terms of power produced by Joule effect.

This paper proposes a novel methodology for calculating a space-varying permeability in HTS bulks, ensuring the same magnetic energy stored in E-J models at each infinitesimal volume. This stationary model is applied for the electromagnetic force calculation in HTS bulks. For the design of HTS bulk machines, multi-objective optimization is necessary to have accurate results. However, due to the nonlinear nature of HTS bulks finite element, Finite Element Analysis (FEA) simulations for optimization are heavily time consuming, even using 2D models, making this approach “infeasible.” The use of equivalent models that guarantee precise results with shorter computation times is then imperative. The method proposed is applied following two basic steps. First, the 3D finite element model is simulated without the bulk to obtain the spatial magnetic flux distribution in the volume where it should be. In the second step, the bulk is included, and the HTS magnetic flux density distribution is obtained using superconducting physics. From these, the HTS equivalent space-varying permeability is computed by the quotient of the two magnetic flux densities. With this, stationary and linear FEA simulations can now be easily performed for the computation of electromagnetic forces in design problems. The proposed method was validated using simulation and experimental tests based on YBCO/GdBCO permanent-magnet force interactions. These results show that, with a previous general study of the geometry to optimize, the equivalent model can be used for optimization purposes, greatly reducing the computational time.

High temperature superconducting (HTS) cables have advantages of low loss and large capacity transmission. In order to analyze and protect the HTS cable, especially in the transient process, this paper develops a new method to analyze its thermal properties. Based on the structure parameters and actual working conditions of three-phase coaxial (tri-axial) HTS cable a two-dimensional (2-D) axisymmetric finite element simulation model along the axis was built in COMSOL. By coupling first and then decoupling, the temperature distribution was studied under the conditions of cooling, rated current, cryogenic system failure, local hot spot and short circuit fault. This method solves the problem that non-isothermal flow (nitf) is hard to converge under transient conditions, and has the advantages of simple and accurate.

It is inevitable for power transformers to suffer from multiple impacts of short-circuit (SC) current and huge dynamic electromagnetic force in service, which may cause large elastic and plastic deformations. Under the SC fault, the distribution of flux leakage and the amplitude of electromagnetic force may be disturbed by winding deformations or displacement. This paper analyzes the cumulative strain–stress characteristics of transformer windings using a coupled electromagnetic–structural analysis solution. The dynamic electromagnetic force, mechanical stress, and plastic deformation are calculated by the 3-D finite-element method. An example of a two-winding 110-kV transformer is simulated. It is found that an initial and slight deformation in windings may influence the magnetic flux distribution. The changed flux density may enlarge the applied electromagnetic force in the windings. The cumulative model and simulation results of this paper may be useful for investigating the winding deformation state prediction.

High-temperature superconducting (HTS) DC cables with the merits of light weight, large capacity and low loss provide a novel power transmission method for future utility grid. In this paper, the electromagnetic characteristics of unipolar and bipolar coaxial HTS DC cables are compared by finite element simulation. Besides, the 3D magnetic flux density distribution characteristics of HTS DC cable are obtained. The method to investigate the influence of winding angle on HTS DC cable magnetic flux density is also applied to 3D HTS DC analysis.