Large Electromagnetic Force Research Articles

Novel multi-layer field shaper in electromagnetic manufacturing process technology of tube joining for uniform deformation

Electromagnetic joining technology is widely utilized in assembling tubular components due to its ability to exert uniform magnetic pressure. To augment this pressure, a field shaper structure has been introduced. However, the conventional design may impair the uniformity of deformation, particularly at the seam. This study presents a novel multi-layer field shaper (MLFS) to enhance deformation uniformity. The performance of the MLFS was evaluated and optimized through experimental trials and simulation analysis. The results showed that MLFS achieved a 300 % increase in minimum deformation with a 56 % reduction in the aspect ratio, demonstrating that our design effectively balances efficiency with deformation uniformity. The magnetic cubic decay formula could fit the simulation data well with R2 higher than 0.999. MLFS was found to enhance uniformity by creating a more even magnetic field that decreased the curvature near the plastic hinge. Compared to altering the interlayer thickness, adjusting the interlayer angle can further enhance uniformity. When the rotation angle is 60°, the radius range can be further reduced by 32.5 %, 39.0 %, and 12.2 % at energy levels of 27 kJ, 30 kJ, and 33 kJ, respectively. The above results indicate that by designing and optimizing MLFS, sufficiently large and uniform electromagnetic forces were obtained.

Short‐Circuit Point Estimation Method for Distribution Lines Using Smart‐Meters

The presence of a substantial short‐circuit current generates a large electromagnetic repulsive force. The energy of such a short‐circuit current increases the likelihood of equipment damage. Furthermore, the occurrence of short‐circuits disrupts the stable supply of electric power. When a short‐circuit occurs in a distribution line, short‐circuit point identification is realized based on information such as overcurrent indicators and equipment damage caused by the short‐circuit. However, there is no established method for promptly pinpointing the short‐circuit location. Therefore, this study proposes a short‐circuit point estimation method for distribution lines using smart‐meters; whose performance is anticipated to improve in the future. The proposed method involved using smart‐meter voltage measurements to measure and determine the changes in the voltage drop slope, caused by the distribution‐substation short‐circuit currents and load currents, from the short‐circuit location to the end point. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Influence of HTS tape arrangement on the transverse compression performance of copper former CORC cables

CORC cables are subject to large transverse compression electromagnetic forces in fusion projects. Unfortunately, the electromagnetic force exceeding its critical transverse compression load will cause an irreversible decrease in its critical current. Therefore, it is particularly important to enhance the critical transverse compression load to ensure that the critical current does not decrease during operation. The winding method of high temperature superconducting (HTS) tape on the central former is variable. So the experimental study on how to increase the critical transverse compression load of CORC cable by changing the winding method of HTS tape is carried out in this paper. Firstly, the influence law of parameters of the number of HTS tapes per layer and the number of HTS tape layers on their transverse compression performance are analysed independently. The results indicate that increasing the number of HTS tapes per layer and the number of HTS tape layers can both improve the transverse compression performance of CORC cables. Whereas, in the case of a cable with a certain critical current demand (the same total number of HTS tapes), increasing the number of HTS tape layers necessarily reduces the number of HTS tapes per layer. Therefore, in order to compare the degree of influence of the above two parameters, we conducted transverse compression experiments on multiple groups of CORC cables with different winding methods (more layers with few tapes per layer or few layers with more tapes per layer) under the same critical current demand. The results show that under the same critical current demand, choosing the winding method that reduces the number of HTS tape layers and increases the number HTS tapes per layer can effectively improve the transverse compression performance of CORC cables. A 3D multilayer CORC cable transverse compression finite element model is also established to explain the inherent reasons for the differences in transverse compression performance of CORC cables under different HTS tape winding methods.

Influence of cracks on nonlinear motion of high-temperature superconducting magnetic levitation system

The magnetic levitation system of a high-temperature superconductor (HTSC) has nonlinear vibration under external excitation, in which the HTSC is subjected to a sizable electromagnetic force. The high-temperature superconducting block is a brittle material, which will crack when subject to heavy pressure. Microfracture of superconductors is inevitable, especially in superconducting magnetic levitation systems. Our paper studies the fracture behavior of a YBaCuO superconducting magnetic levitation system under a large electromagnetic force based on nonlinear bifurcated motions. The E − J constitutive model and the current vector T method are applied to obtain the electromagnetic force of the bulk superconductor during vibration. We analyze the effects of five lengths of the central crack on vibration displacements, the electric field distribution, and the electromagnetic force of superconductors. Without damages, the system does not have apparent bifurcation motion. For the inner cracks, the system has obvious bifurcation motions. The results show that the cracks have a meaningful influence on the nonlinear vibration of the superconducting magnetic levitation system. The displacement of the suspended permanent magnet in bifurcation motion increases with the increase in the crack length, and the collision occurs when the crack length reaches 15 mm.

Characterization of Electromechanical Delamination Behaviors in Practical REBCO Coated Conductor Tapes Under Transverse Tension at 77 K

In high-temperature superconducting coils, the high transport current density and magnetic field generate a large electromagnetic force on REBCO-coated conductor (CC) tapes. A large Lorentz force can cause interlayer delamination damage to the CC tape under radial or transverse tensile loads. The structural delamination characteristics of multilayered REBCO CC tape are essential for the fabrication of mechanically reliable CC coils. In this study, the electromechanical delamination behaviors of practical REBCO CC tapes were characterized using an anvil test method. Our recently established continuous critical current, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> measurement system was used to minimize the test time and can directly evaluate the effect of the transverse tensile load on I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> behavior without time-consuming intermittent I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> measurements during testing. Characterization of the delamination mechanism, including damage initiation, was performed through scanning electron microscopy observation of the fractured sample. Two-parameter Weibull distribution analysis was used to specify the data scattering of the electromechanical delamination strength.

Short-Circuit Performance Analysis of a Distribution Transformer Using Coupled Field-Circuit Approach

The inability of power transformers to resist a short-circuit (SC) fault significantly impacts the safety of power systems. During SC faults, the leakage field undergoes significant distortion, resulting in large SC electromagnetic forces (EFs), which results in critical mechanical stresses. The finite element method (FEM) might be one of the best non-destructive numerical methods that enable designers to assess the transformer SC performance. Using the FEM, most SC performance analysis studies assume either the three-phase (LLL) or the single-phase-to-ground (LG) SC fault. Moreover, the existing studies use an excitation method that provides a high error rate due to the sensitivity of transient solvers. Furthermore, no considerable attention has been given to analyzing the influence of grounding the wye-connected windings on the SC performance. In this work, a non-linear-transient field-circuit coupled 3-D finite element model is created to analyze the SC performance of a delta-wye connected distribution transformer under various SC fault conditions. Results show that grounding the secondary windings significantly impacts the performance when a LG fault is applied. Except for the LG fault with wye configuration of the secondary windings, the windings SC current and EFs decay/rise over time with an exponential trend till reaching steady state.

Dynamic prediction model of segmented combined electromagnetic launch weft insertion for super-wide width industrial fabrics

Stable, reliable and high-speed weft insertion is an urgent challenge for high-speed industrial textile weaving devices. More stable and large electromagnetic forces can be provided by the segmented combined electromagnetic launch weft insertion, compared to the conventional electromagnetic launch weft insertion, which facilitates the realization of high-speed weft insertion. For digital electromagnetic launch weft insertion textile devices, it is necessary to respond quickly to the signals fed back by the sensors. Therefore, a fast and high-precision dynamical model capable of characterizing the kinematic properties of the weft inserter is extremely essential for control, which is conducive to the stable and reliable operation of the device. In this paper, we consider the electromagnetic force, weft yarn tension, air resistance, pipe wall friction, and gravity during the movement of the weft inserter, and establish a dynamic prediction model of segmented combined electromagnetic launch weft insertion (DPMSCEI) for control. Combining simulations and experiments to evaluate the performance of DPMSCEI validates the effectiveness and professionalism of DPMSCEI in solving electromagnetic weft insertion dynamics.

Study on Driving Characteristics of MEMS Electromagnetic Coil Using in the UAV

The miniaturization and swarm design of unmanned aerial vehicle (UAV) is a research hotspot. For the current electromagnetic drive mode, the electromagnetic drive device is too large to be integrated in the current technology. This paper presents a new micro electromagnetically driven MEMS driving device, in which the electromagnetic coil is small in size, with a large electromagnetic force. We firstly designed and calculated the geometric structure of the electromagnetic coil, and analysed the model using COMSOL multiphysics field simulation software. We then carried out a parametric simulation of the electromagnetic coil. The simulation result shown that the error between theoretical calculation and the simulation of the mechanical and electrical properties of the electromagnetic coil was less than 2% under the same size. It provides an idea for UAV miniaturization design.

Structural optimization design and numerical analysis of in-vessel magnetic compression coils

An FRC (field reversed configuration) device HUST-FRC (HFRC) is under construction at Huazhong University of Science and Technology, and the magnetic compression experiments will be investigated. 22 compression coils installed inside the metal vacuum chamber are designed with a peak current of about 110 kA rising within 50 μs. The coils are subjected to large electromagnetic forces during the compression process, which will challenge the structural stability of the coils. Therefore, it is necessary to estimate the structural stability of the compression coils during the compression progress. The compression process involves complex physical problems such as the coupling of circuit-electromagnetic-thermal-mechanical and non-linear contacts between adjacent coil components. It is also a challenge to calculate the coil current, electromagnetic load, and structure stress. To solve these problems, a joint analysis method is developed based on a two-dimensional (2-D) circuit-electromagnetic-thermal model and a three-dimensional (3-D) electromagnetic-mechanical model. The submodeling method is employed in mechanical simulations to improve the efficiency of coil optimization design. The electromagnetic and mechanical results confirm that the design of the compression coils is valid and feasible.

Analysis and design of in-vessel magnetic compression coil system for HFRC

A field-reversed configuration (FRC) experiment facility HUST-FRC (HFRC) is being built at Huazhong University of Science and Technology, where the magnetic compression of FRC will be investigated. To generate a pulsed compression magnetic field, a compression coil system is under development, consisting of in-vessel compression coils, a pulsed power supply, and feedthroughs. Energized by the pulsed power supply, a large current peaking ∼110 kA within 50 μs is transferred to in-vessel compression coils across the feedthroughs. This article presents the analysis and design of the compression coil system. At first, field ripple optimizations are performed to reduce the axial and toroidal ripples within 5%, resulting in an optimized coil arrangement and an improved coil conductor structure. In addition, the power supply circuits are quite complex due to the strong electromagnetic couplings among the coils and between each coil and the metal chamber wall. To rapidly and accurately design the electrical parameters of the pulsed power supply for achieving the target coil currents, a decoupled optimization method based on a circuit-electromagnetic model and a decoupled equivalent circuit model is proposed. The errors of the coil currents and the magnetic field are within 1%. Lastly, a feedthrough design and an optimized feeder scheme are proposed to achieve the structural stability of the feedthroughs since they are subjected to large electromagnetic forces.

Experiments and non-linear MHD simulations of hot vertical displacement events in ASDEX-Upgrade

Hot vertical displacement events (VDEs) are one of the worst case scenarios for high-current tokamaks as they are associated with large heat loads and electro-magnetic forces. Non-linear magneto-hydrodynamic (MHD) simulations of the thermal and current quench can help to understand their dynamics and consequences. In order to make predictions for future devices, the validation of codes against present machines is crucial. Dedicated experiments were performed in ASDEX Upgrade to provide a basis for simulations with the non-linear extended MHD code JOREK. 2D as well as non-axisymmetric simulations at realistic parameters can reproduce quantities like the edge safety factor q 95 at the thermal quench onset, the halo current magnitude and the level of vertical forces, while the exact width of the halo current area requires more sophisticated boundary conditions and is left for future work. Small horizontal forces are observed during the hot VDEs in the experiment as well as in the simulations.

Development of High Strength and High RRR Aluminum-Stabilizer for Superconducting Cable in CEPC Detector Magnet

For the development of a large-aperture superconducting detector magnet in circular electron-positron collider (CEPC), super-conducting cables consisting of Nb-Ti/Cu wires and aluminum stabilizer are essential in both handling large electromagnetic forces during normal operation and redistributing the operation current of tens of kiloampere in case of a quench. High-purity aluminum stabilizer offers extremely high residual resistivity ratio (RRR) for quench protections, however, is too ductile to withstand huge Lorentz forces. Doping technology have been studied in detail in this paper to improve the yield strength of 4N8-aluminium (99.998%) while minimizing the reduction of RRR. All aluminum-alloy samples are characterized by a GM cryocooler for the measurement of RRR and by the standard tensile test facility for the measurement of 0.2% yield strength. It is found that by doping in Ni-0.025% Be-0.025%, annealing at 430 °C, cold-working hardening (∼21%), and curing at 130 °C for 15 h, the resultant aluminum alloy obtains an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p0.2</sub> of 75 MPa at room temperature and a RRR of 417, meeting the basic design requirements of the superconducting detector magnet for CEPC.

Failure analysis of a heavy gauge fastener of the ITER toroidal field gravity support system

The Gravity Supports (GS) of the ITER Toroidal Field (TF) coils are positioned at the bottom of the machine and are situated under the 18 toroidal field coils. Each support includes 26 high strength bolts with M60 and M85 gauge. The TFGS will sustain a total load of about 11,000 tonnes of dead weight of the magnet system. Moreover, they will be exposed in operation to large electromagnetic forces and possible seismic dynamic loads. The bolts are manufactured from forged rods of double aged UNS N07718 (also known as Inconel® 718), a high strength nickel base superalloy. Stringent material specification and quality controls requirements apply to the threaded bolts and the other components of the GS. A complete break of one M85 bolt was discovered, that occurred about 40 days after its installation and preloading, prior to the application of any operating stress. Half of the part blew out from the bolthole and was found lying horizontally on the GS top area. Following the incident, a comprehensive failure analysis was carried out, based on a combination of non-destructive and destructive examinations including advanced techniques such as computed microtomography, immersion ultrasonic testing (UT) and fracture mechanics. The delayed rupture was understood as due to a combination of cavities not closed by the forging operations associated to a continuous network of brittle secondary phases at the grain boundaries, resulting in a local lack of ductility, poor impact toughness and mechanical properties locally lower than specified. As a consequence of the incident, UT procedures were developed to confirm that the remaining bolts, including the installed ones, are free of cavities using sufficiently conservative criteria and fit for purpose prior to operation. In particular, in-situ axial inspections allowed installed bolts that could contain relevant imperfections to be identified and replaced.

Numerical analysis of the contact resistance in a no-insulation layer-wound coil with a simplified electromagnetic–mechanical model

An increase in the contact resistance of a no-insulation (NI) high-temperature superconducting coil was observed in high-field tests, which may be related to the mechanical deformation and the separation between adjacent turns in the coil. The large electromagnetic force generated in the high magnetic field can causeseparation between adjacent turns of the NI coil, which can affect the contact resistance of the magnet. An electromagnetic–mechanical model is built to study the effect of separation on the contact resistance and field delay time of an NI layer-wound coil. The numerical results show that the large electromagnetic force generated in the high field leads to the local separation between adjacent turns and the increase in contact resistance of the NI layer-wound coil. Moreover, a higher external field or target current can result in a larger area of separation, a higher contact resistance and a shorter characteristic field delay time. An overband can restrain the mechanical deformation and separation between turns of the NI coil in the high field, which suppresses the increase of turn-to-turn contact resistance.

Prediction of strain, inter-layer interaction and critical current in CORC® wires under axial strain by T-A modeling

Superconducting conductors on round core (CORC®) cables and wires can meet the needs of large high-field magnets, such as particle accelerators and compact nuclear fusion machines, due to their simple cabling process, high current-carrying capacity and reliable operation under high mechanical stresses. Many high-field magnets require CORC® cables to carry a current of thousands of amperes in a background magnetic field exceeding 20 T. As a result, the large electromagnetic forces will deform the cable in the axial direction due to hoop stress and in the transverse direction by compressive stress. Therefore, it is essential to determine the irreversible deformation limit of the CORC® cable under axial tensile load and optimize the cabling parameters to potentially extend this limit. Analytical and numerical methods are developed to assess the performance degradation of CORC® wires under axial tensile load. The strain level, interlayer contact pressure and friction and their impact on the critical current are calculated by combining the mechanical response and the T-A method. Analyzing the results shows that the winding angle of the tape and the Poisson’s ratio of the inner core are key factors affecting the irreversible tensile strain limit of CORC® wires. The smaller the winding angle and the higher the Poisson’s ratio of the inner core, the higher the irreversible tensile strain limit. For multi-layer CORC® wires, the initial contact pressure caused by the cabling process must also be considered. The inter-layer interaction is coupled with the tape strain of each layer. The results of this research can serve as a basis for optimizing and designing CORC® wires with extended irreversible strain limits.

Multiscale structural assessment of toroidal field coils via reduced-order models

In a tokamak fusion reactor the confinement of the plasma is guaranteed primarily by a series of Toroidal Field Coils (TFC). The TFCs generate a toroidal magnetic field, and must typically withstand large electromagnetic forces. A constant-tension theoretical approach is commonly applied to define an ideal TFC profile, equilibrating in-plane load distributions without shear and bending effects. This paper focuses on the effectiveness of reduced-order models to analyse the TFC mechanical response when also non-ideal shapes are considered. Different beam models are introduced by referring to different treatments of shear and bending effects. A bottom-up homogenisation technique is employed in order to account for the subscale arrangement of TFC components, allowing also to deduce quantitative indications on average localisation effects. The considered beam theories have been specialised to quantify the discrepancies in the macro-micro TFC mechanical response when arc-based approximations are considered instead of the ideal TFC profile. The successful comparison with numerical benchmark solutions, defined by detailed three-dimensional Finite Element models, confirm that beam-like approaches may be considered reliable in a preliminary design stage.

Analytical solution of tokamak vibrations during axisymmetric plasma disruptions

Tokamaks are structures containing a massive supporting structure housing a vacuum vessel with hot plasma. Due to the vacuum vessel heating and temperatures up to 500 ⁰C as for the COMPASS-U, flexible connections need to be used between the main support and the vacuum vessel to accommodate the thermal expansion. Large electromagnetic forces are generated during plasma disruption events, such as Vertical Displacement Events (VDE), inside the vacuum vessel and in the coil system: Central Solenoid (CS), Poloidal Field (PF) coils and Toroidal Field (TF) coils directly attached to the support. In the present paper a parametric analytical model of tokamak vibrations due to axisymmetric plasma disruptions was presented, allowing predictions of the vacuum vessels and the main tokamak structure displacements, velocities and accelerations as well as the dynamic forces transmitted to the foundations. A tokamak was modelled as a 2 DOF dynamic system, including the mass of the main support and the vacuum vessel and the axial stiffnesses and damping values of their supports. A close-form analytical solution was found assuming proportional (Rayleigh) damping for the most general shape of the force functions – described with a series of piecewise linear functions. The electromagnetic forces during axisymmetric VDE were derived from a dedicated 3D model. Detailed solution for the most recent design of the COMPASS-U tokamak was presented, as well as a number of parametric studies checking the sensitivity to the design parameters. The conditions at which large part of the electromagnetic force is transmitted to the concrete foundations were identified. The accuracy of the derived analytical solution was verified with direct numerical integration of the equations of motion.

The Electromagnetic and Structural Analysis of CFETR CSMC Double Current Lead

Before the formal fabrication of central solenoid coil for China Fusion Engineering Test Reactor (CFETR), the R&D of a prototypical coil namely the Central Solenoid Model Coil (CSMC) is performed to accumulate the design and fabrication experiences in the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). As one of the most important auxiliary components, current lead plays the role of transmitting large current from power supply to CSMC winding packs. Of the total 8 sets of current lead, six of them are double current lead. Once CSMC is energized, large electromagnetic force is induced due to the interaction of current flowing in the current lead and back ground magnetic field. And the stress is generated subsequently under the action of electromagnetic force. If the maximum stress is beyond the material strength assessment threshold, the structural design of the double current lead must be redeployed. In order to check the feasibility of the current design of CSMC, the double current lead located in the high field region is selected and the electromagnetic calculation and electromagnetic-structural coupling analysis are carried out subsequently. In the end, the stress in evaluated based on analytical design. The study in the paper will provide reference for the following design optimization of double current lead.

Dynamic Bolting Analysis of Centerstack Casing G10 Ring for NSTX-U

A new dynamic bolting analysis has been conducted to verify the design quality of a G10 ring for the National Spherical Torus Experiment Upgrade (NSTX-U). The G10 ring under the centerstack casing and lower skirt plays a critical role in NSTX-U with large electromagnetic forces during plasma drifts, quench, and halo currents. Inspections of the installed condition of the G10 ring showed a poorly shimmed interface between the ring and the toroidal field flags. This paper will describe how to define the bolt preload to resolve this underperformance issue with the G10 ring by transient bolting analysis. The simulation results of transient bolt reaction forces show that the loads imposed on the G10 ring are within the tested capacity of the Keenserts and G10 ring.

Design and verification status of COMPASS-U vacuum vessel and stabilization loop

The COMPASS-U is a new tokamak in the design phase at Institute of Plasma Physics, Prague, Czech Republic. It is a medium-sized tokamak with high magnetic field (Bt = 5 T) and high temperature vessel (< 500 °C). Hence, large electromagnetic forces are expected on the Passive Stabilizing Plates (PSP) and Vacuum Vessel (VV) during plasma disruption events. A non-selfconsistent approach is selected for the electromagnetic calculations using ANSYS Maxwell software to determine the highest probable forces on passive structures and to design a robust vacuum vessel.This paper outlines the latest status on the design activities of the vacuum vessel concept and its mechanical verification against the electromagnetic forces. The vessel design concept is developed considering the spatial constraints, fabrication simplicity, minimum cost and the design is verified for minimum deformation and stresses in the vessel. It also includes the design evolution of PSP, PSP support and VV support. The mechanical analyses are carried out for load combinations of plasma transient events.