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Bubble formation from paper insulation during overload is important to understand because it can cause a transformer to fail. This phenomenon has been investigated in a mineral oil-paper system, but not in vegetable oil. This study investigated bubble formation during overload in a vegetable oil impregnated paper system and the results were compared to a mineral oil (Shell Diala B) which was studied previously using similar test equipment and method. The limiting hot-spot temperatures for bubbles and water droplets in vegetable oil for paper with water content between 1 - 6 % were determined. The water content of paper measurement which is critical when setting the winding temperature limit was evaluated using both a moisture sensor and Karl-Fischer titration method. [ABSTRACT FROM AUTHOR]

High voltage circuit breakers (HVCBs) play a critical role on providing the desired reliability, and resiliency in power systems. In order to extend their lifetime and predict the failures, various maintenance policies could be applied on these critical components. Amongst these strategies, condition-based maintenance (CBM) provides a satisfactory agreement with future smart environment. This paper aims to provide an insight into the relevant developments in this subject and to explore the viable visions compatible with future research stream. Accordingly, three directions, i.e., diagnostic signals, intelligent modelling and using monitoring data in asset management have been addressed in this paper. It presents challenges dealing with real-time assessment of the diagnostic signals relating to measurements, and analyses. Subsequently, the issues associated with using artificial intelligent (AI) and Machine learning for providing intelligent algorithms have been discussed. Finally, the connection between the monitoring data and the asset management approach is investigated. The latter is looking for the subjects including remaining lifetime estimation, prioritization, and health index definitions. This paper has attempted to make a bridge from past to future research trends in the failure diagnosis of HVCBs. [ABSTRACT FROM AUTHOR]

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

Accurate knowledge of the natural frequencies and shapes of corresponding standing waves are essential for gaining deeper insight into the nature of response of coils to impulse excitations. Most of the previous analytical studies on coils assumed shape of standing waves as sinusoidal but numerical circuit analysis and measurements suggest otherwise. Hence, this paper revisits the classical standing wave phenomenon in coils to ascertain reasons for this discrepancy and thereafter extends it by analytically deriving the exact mode shape of standing waves for both neutral open/short conditions. For this, the coil is modeled as a distributed network of elemental inductances and capacitances while spatial variation of mutual inductance between turns is described by an exponential function. Initially, an elegant derivation of the governing partial differential equation for surge distribution is presented which is then analytically solved, perhaps for the first time, by the variable-separable method to find the complete solution (sum of time and spatial terms). Hyperbolic terms in spatial part of solution have always been neglected but are included here, thus, yielding the exact mode shapes. Voltage standing waves gotten from analytical solution are plotted and compared with simulation results on a 100-section ladder network. The same is measured on a large-sized single layer coil. So, it emerges that, even in single layer coils, shape of standing waves deviates considerably from being sinusoidal and this deviation depends on spatial variation of mutual inductance, capacitive coupling, and order of standing waves. [ABSTRACT FROM AUTHOR]

In this paper, we describe a cooling system for a high temperature superconducting (HTS) magnet of 10 MW class superconducting wind power generator (SWPG). To cool the HTS magnet below 35 K, a novel neon-helium hybrid cooling system is proposed. Neon cools the heat exchanger based on the thermosiphon principle and a cryogenic blower forcibly circulates helium gas between the heat exchanger, attached to a rotating neon vessel, and the HTS magnets. This cooling system has two advantages: applicability to large rotating HTS magnets and high reliability by removing a cryogenic or a high-pressure rotating coupling. To verify the performance of this cooling system, a lab-scale performance evaluation system(PES) is designed. The PES will be proved by cooling the generated heat and penetrated heat of the HTS magnets during operation. This paper describes the detail design process and the preliminary test results of the fabricated cooling system. [ABSTRACT FROM AUTHOR]

Maglev technologies have been extensively studied for modern transport systems; however, their main applications are limited to transportation systems with fixed tracks. On-road vehicles could have a broader outlook if combined with maglev technologies, for which electrodynamic wheels (EDWs) have provided a possible solution. Conventional EDWs are designed based on permanent magnets (PMs), which generate limited thrust and lift forces while having a low power density. In order to enhance the feasibility of EDWs in maglev vehicles, a novel design of EDWs based on high-temperature superconducting (HTS) Halbach array magnets (HAMs) has been proposed in this paper. The suggested design is made of the second generation (2G) superconducting coils, which have been modeled with the A-formulation and T-formulation based finite element methods. Simulation results show that the proposed HTS HAM EDW can generate higher thrust and lift forces, improve the magnetic flux density distribution in the airgap, and greatly reduce the weight of the magnets compared with the conventional design. This paper provides a possibility for future on-road maglev vehicles. [ABSTRACT FROM AUTHOR]

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

This paper investigates the influence of stator/rotor pole number combinations and permanent magnet (PM) numbers on electromagnetic performance of consequent-pole hybrid excited flux reversal machines (CP-HEFRMs), which have different numbers of PM poles and iron poles and concentrated AC and DC windings on the stator and a salient pole rotor. PMs in the slots of one stator pole are magnetized radially in the same direction, while opposite on adjacent stator poles. Magnetic field paths of DC, PM, and hybrid excitations are investigated. The phenomenon of flux cancellation, i.e., PM and DC MMFs in CP-HEFRMs are of opposite polarities in the flux-enhancing operating mode, is revealed and verified, for the first time, as the key feature that makes CP-HEFRMs different from other hybrid excited machines. Consequently, the saturation in stator pole and yoke can be mitigated and hence the overload capability of DC excitation is enhanced, which is verified by finite element analysis (FEA). Global optimizations are utilized to obtain the optimal rotor and stator pole number combinations and PM numbers for each stator pole. Torque, torque ripple, inductance, unbalanced magnetic force, and flux regulation capability are compared for different PM numbers and rotor pole numbers. Comparisons are made on consequent-pole and non-consequent-pole topologies in terms of torque capacity, flux regulation capability, and PM consumption to further illustrate the advantages of consequent-pole topology. A prototype machine is built and tested to validate the analyses. [ABSTRACT FROM AUTHOR]

Numerous research efforts are devoted to attain high performance and strong fault tolerance for the machine drives in safety critical applications, though the two aspects are conflicted in most cases. In this paper, a novel triple 3-phase PMA-SynRM with star-delta connected windings is proposed. The star-delta winding could produce a higher fundamental magneto-motive force and lower spatial harmonics than the conventional star winding. Therefore, it exhibits higher torque, lower torque ripple and lower iron loss, enhancing the healthy performance. In addition, the coils whose turn fault current is the highest are arranged in the inner delta part which provides circulating current path. It is demonstrated that the proposed winding solution reduces the fault current by 55% and the fault turn copper loss by 65%. Hence, the machine's fault tolerance is significantly improved. The machines with the star winding and star-delta winding are studied by detailed finite element calculation and experimental tests under various operation modes. Both the simulation and test results confirm that the proposed star-delta winding machine owns higher performance and stronger fault tolerance than the conventional star winding machine. Thus, it becomes a more competitive candidate for the high reliability drives. [ABSTRACT FROM AUTHOR]

In this paper, a dual-rotor slotless axial-flux permanent magnet (AFPM) motor with equidirectional toroidal winding (ED-TW) is proposed and compared with the AFPM motor with traditional toroidal winding (T-TW) with the same dimensions, number of coils and poles. Different from the T-TW, only the positive sides of coils of the ED-TW are left on one side of the stator core, the return sides of the coils are all removed to the other side of the stator core. Firstly, the structure and operation principle of the two motors are introduced and analyzed. To clarify the features of the ED-TW, the synthetic electromotive force (EMF) vector and armature reaction field of the ED-TW and T-TW are studied. Secondly, the main size equations of the AFPM motors with toroidal windings are presented. Subsequently, the electromagnetic characteristics of the AFPM motors with ED-TW and T-TW are analyzed and compared based on the three-dimensional finite element method (3D-FEM). The comparison results indicate that the AFPM motor with ED-TW has superiority in torque density and efficiency. Finally, a prototype of the AFPM motor with ED-TW is manufactured and tested, which validates the feasibility of the proposed motor and the correctness of the analysis of the 3D-FEM. [ABSTRACT FROM AUTHOR]

This paper presents a new linear eddy current speed sensor with rectangular-shaped coils. The excitation coil and the pick-up coil have a perpendicular configuration without a magnetic yoke. The proposed sensor is shorter than the previous designs. The sensor works for a conductive moving target; in this paper we present calculations and an experimental verification for solid iron and aluminum moving part materials. A novel 3D analytical method is presented for the description and for the design of an eddy current speed sensor that is fast and has high precision. The source fields and the reaction fields caused by induced eddy currents are separated in our 3D analytical method, which facilitates an enhanced investigation of the features of the speed sensor. Evaluations of the effects of the moving part material and of coil lift off on the performance of the speed sensor are made with the use of a 3D analytical method. Measurements are performed for an eddy current speed sensor at different speeds up to 11.65 m/s and at different frequencies with a novel analytical model in terms of the induced voltage in the pickup coil versus speed. Simplicity and high precision are the main advantages of the proposed speed sensor. The achieved linearity error is 0.47% (measured) up to 11.6 m/s, and 0.43% (calculated) up to 117 m/s (420 km/h). [ABSTRACT FROM AUTHOR]

To commercialize wirelesselectric vehicle charging (WEVC), three critical issues must be resolved: communication between the vehicle assembly (VA) and the ground assembly (GA), metal object detection (MOD) on the GA coil, and position detection (PD) of the VA. This paper proposes a comprehensive system that integrates MOD and PD with VA-GA near-field communication (NFC). A common high-frequency aided carrier is used not only for NFC, but also for MOD and PD. In addition, an array of dual-purpose detection coils is proposed as a sensor for MOD and PD. As a result, the three functions listed above share numerous components and circuits, greatly simplifying the system structure. Furthermore, because the high-frequency aided carrier can operate with or without a power carrier, the preceding three functions are independent of system power status. The proposed method has been validated using a 3.3 kW WEVC prototype operating at 85 kHz. The experimental results show that the proposed system is capable of performing both online and offline NFC, MOD, and PD with high sensitivity while having no impact on wireless charging efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes a novel algorithm which made it feasible to predict the harmonic fault signatures under dynamic eccentricity in Permanent-Magnet synchronous machines with concentrated non-overlapping winding for any slot-pole combination. In the literature, only the appearance of the fractional harmonic components related with the pole number has been proposed but there are no studies to predict which exact components will rise in each topology. Initially, a mathematical equation is derived for the machine EMF under dynamic eccentricity based on the air gap permeance model. Later on, the terms of this equation are inserted in a Fault Signature Block Binary Array in which the position of each cell expresses a specific harmonic frequency component. After substitution of the machines parameters, the array results with zero and nonzero terms. The positions of the nonzero terms express the frequency components excited by this particular fault. 3-D FEA and experimental results of a Permanent-Magnet Axial-Flux Machine are used to validate the proposed algorithm. [ABSTRACT FROM AUTHOR]

The torque ripple of a switched reluctance motor (SRM) should be taken into account, as it can have negative effects on a connected gearbox and/or load. In this paper a concept and two realization methods for the reduction of the torque ripple are presented. An optimized alignment of the active elements of the stator leads to a reduction of this torque ripple. The first method proposed here is a four-fold segmented motor, which can reduce the torque ripple by 37.3 %. This can be achieved by segmentation in combination with a clever arrangement of active elements. However, this increases the number of necessary inverters, which increases redundancy and therefore leads to more security. A second method of achieving an equal reduction can be obtained by using a “double stator” motor. In this configuration both stators can be powered together. With this concept, the number of converters is halved compared to the first mentioned solution. This saves electronic components and thus reduces the effort. All results referred to in this article are obtained by simulation, or measured on a prototype. [ABSTRACT FROM AUTHOR]

Effective management of emerging medical devices can lead to new insights in healthcare. Thus, human body communication (HBC) is becoming increasingly important. In this paper, we present magnetic resonance (MR) coupling as a promising method for the intra-body network (IBNet). The study reveals that MR coupling can effectively send or receive signals in biological tissue, with a maximum path loss of $PL$ $\le$ 33 dB (i.e. at 13.56 MHz), which is lower than other methods (e.g., galvanic, capacitive, or RF) for the same distance (d = 100 cm). The angular orientation of the transmitter and receiver coils at short and long distances also show a minor variation of the path loss (0.19 $\leq \Delta PL\le$ 0.62 dB), but more dependency on the distance (0.0547 dB/cm). Additionally, different postures during the MR coupling essentially does not affect path loss ($\Delta PL\le$ $\pm$ 0.21 dB). In the multi-nodal transmission scenario, the MR coupling demonstrates that two nodes can simultaneously receive signals with -16.77 dBm loss at 60 cm and 100 cm distances, respectively. Such multi-node MR transmission can be utilized for communication, sensing, and powering wearable and implantable devices. [ABSTRACT FROM AUTHOR]

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

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

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

This paper presents a novel leakage model for transformers that includes losses. This new model is physically based (topological) and it is possible to connect it to a topological core model without using any fictitious windings. The methods to calculate its parameters from standard test data and from design data are detailed within the paper. The results show that the new coupled leakage model with losses is able to match exactly the test report, when using standard test data. Preliminary investigations show that the results are very close to measurements, when using design data. [ABSTRACT FROM AUTHOR]

The realization and preliminary tests of a high temperature superconducting axial-field synchronous machine (HTS-AFSM) prototype are presented in this paper. The HTS machine consists of a 3-phase stator with HTS armature winding and a permanent magnet (PM) rotor. The HTS armature winding contains three pancake coils made of BSCCO tape forming a single layer nonoverlapping concentrated stator windings. The rotor is composed of four NdFeB permanent magnets. Several tests have been carried out such as voltage vs. currents curves of the HTS coils, static torque, back-EMF and load tests in generator mode. A 3D semi-analytical model, based on integral equations, has been used to check out the measured electromagnetic quantities. It has been shown that the measured and the calculated quantities are in satisfactory agreement. [ABSTRACT FROM AUTHOR]

Quench has always been an urgent problem for high temperature superconductor (HTS) magnets. Fast discharge of the coil current is an effective method to protect the HTS magnet from quenching. In HTS magnets, metal plates are originally used to provide conduction cooling and mechanical support for the coil. During fast discharging operations, the metal plates can rapidly absorb part of the magnetic energy stored in the HTS coils through electromagnetic coupling. Previous studies are based on copper plates. This paper studies the influence of several promising metal materials on the discharging process of the HTS coils coupled with metal plates by experiments and simulations. The results show that in the explored resistance range, the higher the electrical conductivity of the metal plates, the better the acceleration of the current attenuation of coil at the early stage of discharging process. The effects of different metal plates on accelerating current attenuation of the coil are ranked as follows: SS 304L < Al 6061-T6 < Al (RRR = 30) < Cu (RRR = 30) < Au < Cu (RRR = 300) < Ag. However, Cu (RRR = 300) plates can absorb more energy from the HTS coil than the Ag plates during the discharging process. Copper with higher purity (Cu (RRR = 300)) and silver are promising alternatives for metal plates of HTS magnets. Generally, a fast current drop is always the most effective method for avoiding tape turn-out during a local quench; therefore, silver with the highest electrical conductivity is the best choice in view of quench protection. [ABSTRACT FROM AUTHOR]

This paper reported the fabrication and the test results of the high temperature superconducting (HTS) magnet developed for the aluminum billet heater for aluminum extrusion processing. In this magnet, the HTS coils were combined with iron cores, because the required magnetic field in the working region was about 1T. Two HTS coils wound directly on the convex shape iron cores were fabricated. The HTS coils were made by the no-insulation winding of REBCO tape with the YOROI-coil technique. Each of them was separately installed in an individual cryostat. Two HTS coils with iron cores were disposed oppositely to each other and were magnetically connected by a C-shape yoke placed in room temperature. The HTS coil was cooled down to about 15 K by the GM cryocooler in the initial cooling. The magnetic field of 1.06 T at the center of the heating region was stably generated with the rated current of 200 A. It was also demonstrated that the HTS magnet could be charged up to 300 A without quench. According to the observation of the electromagnetic force direction from the outside of the cryostat, it was confirmed the validity of the force balance design of the magnet. [ABSTRACT FROM AUTHOR]

Objective: The objective of this paper is to model and experimentally validate the path loss benefits of magnetic human body communication (mHBC) using small form-factor-accurate coils operating under realistic conditions. Methods: A radiating near-field coupling model and numerical simulations are presented to show that the magnetic-dominant near-field coupling between resonant coils offers low path loss across the body and exhibits extra robustness to antenna misalignment compared to far-field RF schemes. To overcome the pitfalls in conventional vector-network-analyzer-based measurement configurations, we propose a standardized setup applied to broadband channel loss measurement with portable instruments. Two types of PCB coils for mHBC communication, designed for large devices such as smartphones and small devices such as earbuds, respectively, are built and measured. Results: The mHBC link for the ear-to-ear non-line-of-sight (NLOS) path measures up to −23.1 dB and −31.2 dB with large and small coils, respectively, which is 50 dB more efficient than the conventional Bluetooth channels utilizing antennas of similar sizes. Ear-to-pocket and pocket-to-pocket channels also show at least 16 dB higher transmission than the Bluetooth channel. Conclusion: In terms of path loss, the mHBC approach offers compelling performance for short-range applications over the body region. For coils with dimensions of several centimeters, working between 100 MHz and 200 MHz minimizes the channel loss while keeping the bandwidth above 1 MHz. Significance: The extremely high efficiency of the proposed mHBC channel provides a solution to the energy problem for miniaturized wearables, potentially leading to new wearable device designs. [ABSTRACT FROM AUTHOR]

Urinary bladder volume monitoring can benefit from contactless measurements, as alternative to the traditional medical methods of transurethral catheterization or ultrasound examination. The emerging modality of Magnetic Induction Tomography (MIT) offers the possibility for estimation of the intravesical volume in the physiological and pathological states using conductivity map reconstructions of the tissues present in the pelvic region. Within MIT, eddy currents originating from the conductive urine can produce their own magnetic field in response to an external magnetic source that is susceptible of being detected outside the body by means of a static ring of sensing coils. However, the ill-conditioned and ill-posed nature of the MIT Inverse Problem make the numerical implementation and conductivity estimation highly laborious. In this paper, we present a rotational frame model based on the MIT principles with application in urodynamic studies, which allows to extend the number of contactless measurements without increasing the overall dimension of the simulation domain, at the expense of solving multiple MIT Forward Problems. On the inversion process, the single-step Gauss-Newton method with Laplacian regularizer is recruited to estimate the bladder volume non-invasively and remotely (estimation error of 19%) using a simplified (quasi 2D) approximation to the distribution of eddy currents in the examined region, therefore paving the way for this technique to surpass the current limitations found in intravesical volume monitoring. [ABSTRACT FROM AUTHOR]

Accurate control of molten metal levels during pyrometallurgical smelting operations is critical to improve process decision-making and maximizing production efficiency, such as when to commence tapping and the duration of the tapping operation. In addition, molten metal level control is important for long-term structural integrity of the furnace. Current methods to measure molten metal levels have limited accuracy and are intermittent, as they require manual measurement from above the furnace. In this paper, a continuous measurement system was designed to improve the molten metal level measurement in pyrometallurgical furnaces. This paper describes the tests of an electromagnetic sensing system consisting of eddy current drive and pickup coils that could be embedded in the wall of a furnace. As part of the development, portions of the system were simulated using COMSOL, and a prototype of the key hardware components was built and tested in the laboratory to validate the simulation results. Differential coil hookup provided a low-noise and high-resolution response. The system obtained a molten metal level detection resolution of 5 mm at liftoff distances approximately 300 mm from the simulated metal bath. Projection to latent structures (or partial least square) and regression analyses were applied to signal response to predict metal height, and a good agreement between predicted and measured laboratory metal heights was obtained. Initial results of the prototype system demonstrate its potential to accurately and continuously measure molten metal level, thereby improving safety and control of furnace operations. [ABSTRACT FROM AUTHOR]

This paper aims to propose a new Vernier reluctance machine (VRM), which integrates the advantages of a robust rotor structure, good torque density, and flexible flux control ability. The key is to establish the excitation field with both stator slot permanent magnets (PMs) and zero-sequence current. Two excitation sources have different pole pair numbers but share a parallel magnetic circuit and contribute to superimposed torque in this machine. Meanwhile, a flexible flux control can be achieved by regulating zero-sequence current, and little demagnetization risk exists for slot PMs during flux control. In this paper, the machine configuration and operation principle are introduced, along with its integrated ac and dc drive method. Electromagnetic performance of this new machine is evaluated by finite-element analysis. Leading design parameters are determined and optimized considering optimal injection ratio of zero-sequence current. A prototype is fabricated, and relevant experiment results demonstrate the feasibility of the proposed solution. [ABSTRACT FROM AUTHOR]

In most multiobjective optimization problems of electrical machines, the weighted function method is used to convert them into single-objective optimization problems. This paper applies a kind of new multiobjective evolutionary algorithms (MOEAs), called adaptive multiobjective black hole (AMOBH) algorithms, to achieve effective multiobjective optimization of a tubular coreless linear permanent magnet synchronous motor (LPMSM). To reduce the computation cost of the MOEAs, a one-layer analytical model (AM) is presented for the tubular coreless LPMSM in this paper. The accuracy of the simplified one-layer AM is verified by comparisons with multilayer AM and finite element analysis (FEA) under different structure parameters. It is found that the simplified AM has good accuracy and can decrease the computation cost significantly. AMOBH algorithm is subsequently introduced. The optimal Pareto front with regard to thrust, copper loss, and permanent magnet volume are analyzed, and more diversified optimization results are provided. The final Pareto solution can be selected directly by practical physical values according to the application requirements. Finally, a prototype is fabricated for the selected design; its experimental results are provided and compared with those of the FEA results. [ABSTRACT FROM AUTHOR]

The stator winding acts as a carrier for the electrical load, and its loss accounts for about 50% of the total loss in AC machines. So how to design the stator winding for reducing winding loss is extremely crucial. Some traditional transposition methods are adopted in the winding design for large AC machines. Although they have a certain effect on reducing winding loss, there is still room for the improvement in the winding design and manufacturing technology. In this paper, a new global transposition method of stator winding is proposed. Then a megawatt driving motor is taken as the research object, and the eddy current losses, circulating current losses and total losses of winding strands are calculated by the three dimensional (3-D) finite element method (FEM) which has been validated by the experiment. In addition, by comparison with the two original transposition methods, it is proved that the proposed global transposition method is more effective in further reducing the winding loss, and the winding loss distribution is more uniform. This global transposition method proposed in this paper provides a reference for the optimal deign of the stator winding in AC machines. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) technologies are expected to be a key enabler for lightweight and cost-effective direct-drive (DD) trains for large wind turbines. This paper reports the designing and basic experimental validation of the world's first full-scale DD HTS generator demonstrated on a commercial wind turbine. The HTS generator has its rotor with an HTS field winding working below 30 K, which is achieved by using off-the-shelf Gifford-McMahon cryocoolers. The stator of the generator is essentially conventional, except that the armature winding has four segments to limit fault torques in case of sudden short circuits due to converter failures. Compared to an existing DD permanent magnet generator on the turbine, the air gap shearing stress of the HTS generator is doubled, and the weight is reduced by 24%. The overall design requirements from the turbine integration perspective, as well as the topological considerations, are first described in this paper. The electromagnetic and cryogenic designs are then presented, followed by performance testing of HTS coils. The basic experimental validation shows that the cryogenic design is satisfactory and the measured no-load voltage matches the finite element calculation very well. [ABSTRACT FROM AUTHOR]

In this paper, we present a wireless power transfer (WPT) system with a two-dimensional (2-D) magnetoinductive wave (MIW) device composed by two orthogonal sets of 1-D MIW devices woven together. The device is made by 112 double-spiral coils, a geometry that we have optimized to render a low attenuation propagation. This approach enables a charging area of 22 × 22 cm2 from which a receiver device can be supplied with energy with optimum efficiency from 32 different locations with the use of a single excitation port. We present a detailed optimization of the design and fabrication of the device. To describe the behavior of the device, we use a modeling method based on the impedance matrix that allows us to include all coupling interactions among the increased number of cells. With this method, we are able to find the optimal operating conditions like the location of the excitation and the coupling conditions of the receiver device. With the proposed 2-D MIW device, we can provide up to 5 W to a load of 5  $\Omega$  located at the optimal axial separation. We corroborate our calculations with vector network analysis and dc output power measurements. Furthermore, we demonstrate the device supplying to distinct types of loads simultaneously. This paper is accompanied by a supplementary file showing the required MATLAB script and input files to calculate the mutual inductance between a receiver and the cells of the pad. [ABSTRACT FROM AUTHOR]

Railguns are current-driven guns that allow reaching large muzzle velocities and energies. In the military context, the long-range artillery scenario makes use of these two capabilities to enable the launch of hypervelocity projectiles to target distances above 100 km. As of today, the most advanced railgun project is conducted by the Office of Naval Research, Arlington, VA, USA, and features railguns with a muzzle energy of 32 MJ. Such large artillery railgun systems with efficiencies above 30% are fed by a pulsed power system with a nominal energy content of about 100 MJ. In contrast to this, experiments with French-German Research Institute’s (ISL) most powerful railgun, PEGASUS, have reached muzzle energies of 2 MJ, only. The nearer future ISL has to answer two questions: 1) is the railgun technology adequate for a long-range artillery scenario? 2) can the railgun launch a hypervelocity projectile which is being developed by other groups in ISL? To do so and to support the development of the hypervelocity projectile, a larger railgun installation with a significant increase of the energy and free flight capability is required. In this paper, three different railgun systems were investigated using an electric circuit simulation code. The systems are referred to by the energy being stored in the capacitors as 25, 50, and 100 MJ. The aim of this paper is to investigate what masses can be accelerated to the relevant velocity range for the long-range artillery scenario by these different primary energies. The results of this paper can be used to aid the decision about the required size, with respect to the military scenario, of a potential future railgun system. [ABSTRACT FROM AUTHOR]

Magnetic local positioning systems are a well-suited candidate for reliable indoor positioning systems, as they are robust against blocking by dielectric materials like walls or people. The system presented in this paper is implemented with a one-axis magnetic transmitter and several three-axis field sensors connected to a complete sensor network. Unfortunately, the performance of the system is severely impaired by field sensor nonidealities such as magnetic coupling of the sensor coils, coil misalignment, field sensor rotation, and unsynchronized sampling. In this paper, the overall field sensor impairments and an additive Gaussian noise model superposing the magnetic field are mathematically described. Then, a novel calibration scheme for the overall field sensor nonidealities is presented. Furthermore, a statistically optimal localization procedure coping with the field sensor nonidealities is developed. The proposed novel localization and calibration algorithms are demonstrated in a common office environment with a size of 7 m ${\times }\,\,5$ m ${\times }$ 3 m. Thereby, the calibration impressively reduces the position root-mean-square error (RMSE) from 46.8 to 10.6 cm and the angle RMSE from 24.8° to 6.1°. [ABSTRACT FROM AUTHOR]

To improve power density and motor performance, new bearingless motor topologies combine torque and magnetic suspension coils into a single winding. Of these topologies, the parallel dual-purpose no-voltage winding is advantageous from the bearingless drive perspective because it requires the least amount of hardware. However, this topology can result in undesirable current controller performance from cross-coupling effects between the suspension and torque operation. This paper investigates these cross-coupling effects using rotating reference frame theory to derive relevant system disturbance transfer functions. The nature of this coupling is explained in relation to the machine and control parameters (inductances, resistances, controller gains) to provide insights for bearingless machine and control designers. The paper proposes and simulates different compensation techniques to minimize or eliminate the cross-coupling. It is shown that with careful machine design or with proper feedback control compensation, the motor controller can be implemented as a conventional motor drive, without knowledge of the magnetic suspension system. Finally, experimental validation is provided via two prototype machines. [ABSTRACT FROM AUTHOR]

Domestic induction heating appliances are evolving from surfaces with three to five fixed cooking areas to flexible cooking zones. These are able to adapt to a number of vessels of any size and shape by using multiple coils. Some state-of-the-art induction systems make use of overlapped inductors in two layers, which combine the high efficiency of large inductors with the high flexibility of small adjacent coils. The main drawback of this concept is the unequal distance between different coils and the vessel, which implies that each coil presents a different impedance depending on its layer. This paper presents an induction system conformed by nonplanar inductors. These inductors are designed in such a way that they can be assembled in overlapping structures, while preserving equivalence among them, i.e., they all present the same impedance. This paper includes the finite-element method modeling of the nonplanar coil, an analysis on the an experimental verification. [ABSTRACT FROM AUTHOR]

This paper presents a novel method to estimate the number of shorted turns in a permanent magnet synchronous machine (PMSM) following the detection of interturn short-circuit (ITSC) fault and its location. In this proposed method, PMSM is excited through a low sinusoidal voltage at standstill condition to obtain the winding resistance and synchronous inductance by current response. It is shown that the ITSC fault introduces variation in the current response, which can be used to calculate the number of shorted turns under zero fault resistance assumption. Using this practical procedure, the fault severity can be estimated directly in a straight-forward manner. In other words, the severity estimation for a given machine can be done without complex machine modeling or experiments on ITSC prototype with multiple taps. The findings in this paper are essential for a comprehensive solution including fault mitigation algorithms and postfault operations. In order to verify the findings, a three-phase equivalent circuit model supported by finite element analysis results is used to take saturation and space harmonics into account. In addition, experimental results are presented to demonstrate the validity and practicability of the severity estimation. [ABSTRACT FROM AUTHOR]

In order to ease the manufacture process of very large permanent magnet (PM) machines, such as direct drive wind power generators, modularity technique is usually adopted. Although conventional fractional slot PM machines with all teeth wound windings show good performance, the coils located at the end part of each segment could be easily damaged because of being exposed to the air. In addition, the local winding faults could easily proliferate to the whole machine due to the physical touch of adjacent coils. Thus, a novel modular fractional slot PM machine with redundant teeth is proposed in this paper, while three phases within each set of winding are still balanced. The construction of the proposed modular PM machine having 42-slots/32-poles (42S/32P) combination is described in detail as an example, which can be treated as the integration of six 6S/5P segments and a redundant 6S/2P machine. The reason for using 6S/2P machine is to get rid of the undesirable unbalanced magnetic force (UMF), which usually exists in rotating asymmetric machines, such as 3S/2P PM machine. Since the end part of each segment in the proposed modular PM machine can be covered by half redundant tooth during the production, more protection can be provided for coils located in these regions. Furthermore, the separation of six segments can improve the fault-tolerant capability of the machine. The electromagnetic performance predicted by finite-element analysis (FEA) also demonstrates that the proposed modular machine will perform better if dual three-phase winding is adopted. Finally, the experiments on the prototyped machine validate the analysis in the paper. [ABSTRACT FROM AUTHOR]

Electromagnetic tracking has widely been used in many fields, such as virtual reality, motion tracking, and biomedicine. Especially in surgical navigation systems, electromagnetic tracking offers a cost-effective alternative to traditional X-ray fluoroscopy. In this paper, we present a new magnetic tracking method based on phase difference detection. Two 3-axis magnetic sources and one 3-axis sensor are needed in the tracking system. The position and orientation of the sensor can be obtained simply by measuring the phase difference between the square of the synthetic magnetic induction intensity at the position of the sensor and the square of the excitation current of the magnetic source. The experimental results indicate that this method has a good tracking accuracy and speed. The mean position error is less than 0.1 cm, and the theoretical tracking time can be less than 3.5 ms when the frequency of the excitation current is no less than 1 kHz. Furthermore, antinoise simulations show that the tracking performance of this method is more robust against environmental noise than that of existing methods. Therefore, the electromagnetic tracking method proposed in this paper has good application prospects in many respects. It enables real-time tracking with high accuracy and a strong antinoise ability. [ABSTRACT FROM AUTHOR]

Due to the nonlinear properties of superconductors, modeling of high-temperature superconducting (HTS) devices is difficult, especially for the ones in large scale. In this paper, we develop the multiscale model from a two-dimensional (2-D) planar geometry to a 2-D axisymmetric geometry to successfully calculate ac loss of large-scale HTS coils. By applying appropriate boundary conditions, the infinite-turn coil is built in the 2-D-axisymmetric model to produce approximated current density for an HTS coil. Besides, the multiscale model is improved in terms of coupling, so that submodels can be connected in one file and the external data processing is not needed. Validation on accuracy and efficiency is demonstrated through a double-pancake coil. Results are compared with a conventional model that considers the superconducting characteristics on each turn of the coil in actual size. This paper shows the development and improvement of multiscale model in the 2-D axisymmetric geometry is feasible. Due to its high accuracy and efficiency, the developed multiscale model can be a useful approach to analyze electromagnetic characteristics and calculate ac losses in large-scale HTS magnets. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) technology has become a popular research direction in the field of industrial applications, with the advantages of contactless operation, high degree of freedom, and great controllability. However, there are still some challenging issues that need to be resolved. First of all, more advanced circuit topologies and magnetic coupling structures need to be designed to achieve the power conversion goals of diversified applications. Second, novel control methods, optimization algorithms, and modeling methods enable systems to be better controlled and designed. Finally, potential application scenarios need to be discovered so that this novel power transfer method can be applied in more suitable applications. Therefore, this topic is organized by the responsible editor to gather the power of more scholars. With reviewers' hard work and considerations, 32 papers were finally accepted for publication in this Special Issue. [ABSTRACT FROM AUTHOR]

Due to its low energy consumption and simplicity, near field communication (NFC) has been extensively used in various short-range transmission scenarios, for example, proximity payment and NFC entrance guard. However, the low data rate of NFC limits its application in high rate demanded scenarios, such as high-resolution fingerprint identification and streaming media transmission as well as the future promising high rate indoor communications among pads, phones, and laptops. In this paper, we model and analyze the performance of the orbital angular momentum based NFC (OAM-NFC) system, which can significantly increase the capacity of NFC. We first give the OAM system model. With coils circularly equipped at the transmitter and receiver, OAM-NFC signals can be transmitted, received, and detected. Then, we develop the OAM-NFC generation and detection schemes for NFC multiplexing transmission. We also analyze the OAM-NFC channel capacity and compare it with those of single-input-single-output (SISO) as well as multi-input-multi-output (MIMO) NFC. Simulation results validate the feasibility and capacity enhancement of our proposed OAM-NFC system. How different variables, such as the transceiver misalignment, the numbers of transceiver coils, and transceiver distance, impact the OAM-NFC capacity are also analyzed. [ABSTRACT FROM AUTHOR]

For a marine electrical machine, its high power density and large electromagnetic (EM) load tend to bring high saturation to the magnetic circuit. When the non-linearity of ferromagnetic material is not taken into consideration, large errors will appear in the calculation of air-gap flux density and EM force wave. Considering the radial and tangential EM force waves that cause the stator core to vibrate and deform are the primary sources of EM vibration of a non-salient pole synchronous generator (NSPSG), this paper introduces a semi-analytical method of calculating the radial and tangential EM force waves, with the non-linearity of ferromagnetic material taken into account. The method includes the distributed magnetic circuit method (DMCM), the separation variable method (SVM) and the complex variable conformal transformation method (CVCTM). First of all, the radial air-gap flux density is obtained by using the DMCM to calculate the no-load magnetic circuit of the NSPSG and dealing with the non-linearity of ferromagnetic material by B-H curve. Then, the tangential air-gap flux density is calculated by the SVM and the complex relative air-gap permeance is calculated by the CVCTM to determine the effect of slotting. Finally, the radial and tangential EM force waves are obtained by Maxwell stress tensor method. The proposed semi-analytical method is verified through measuring vibration acceleration of the NSPSG. [ABSTRACT FROM AUTHOR]

Partial demagnetization is a condition that may occur in Permanent Magnet machines due to overloading or thermal stress. Whenthis happens, the magnetic field locally weakens leading to an asymmetry of the air-gap field. This asymmetry will cause harmonics, which will be expressed as extra losses and mechanical oscillations. Moreover, since the field becomes weaker, more current is required to serve the load leading to less efficiency, increased losses and consequently increase of the temperature, which will cause further progression of the demagnetization severity until a total machine breakdown. Several methods have been proposed in the literature for the online detection of the demagnetization, however they have not related the fault to the manufacturing characteristics of the machine, which play an important role on the expected harmonic index and the associated fault signatures. This paper presents for the first time a detailed analytical investigation of the expected harmonics in the stator current spectrum in case of demagnetization, as a function of the stator winding and number of poles. The analytical results are verified by extensive simulations via the finite element method and experimental testing. [ABSTRACT FROM AUTHOR]

This paper proposes a monolayer Halbach array based permanent magnet spherical motor (PMSpM) using cubic permanent magnets (PM). The research aims to provide a fast computing model to calculate the magnetic field for this PMSpM, which helps for future PMSpM optimization and control study. Three thickness equivalence principles are provided and compared for cubic PMs. The magnetic scalar potential is introduced, and the spherical harmonics expansion is implemented for rotor magnetic field analysis. Engineering revision is used to reduce the Legendre function deviation in polar angle direction. Torques and forces are deduced using the Lorentz force law, and relatively simple models of this PMSpM for both magnetic fields and torques are acquired. In addition, a prototype motor has been developed, and the analytic results of air-gap flux density and torque are compared with their finite element simulation and experimental results, which are proved consistent. It is concluded that the fundamental component of the spherical harmonics can be used to present the magnetic field model, which uses fewer integrals than the Biot-Savart law based solution, and the modeling results of the magnetic field flux density, forces and torques are in line with the expectations. The analytic models are proved correct. [ABSTRACT FROM AUTHOR]

Design of radial passive magnetic bearings with active dampers (radial PMB-AD) and their application in a down-hole natural gas compressor (DHGC) are discussed. These compact and reliable bearings allowed noncontact suspension of a high-speed DHGC rotor spinning at 50 kr/min in a highly adverse environment more than 3 km (10 000 ft) below the ground with temperatures reaching 100 °C. The design was further complicated by the space limitations imposed by a well casing. The paper presents the design of PMB-AD modules, as well as their integration and testing as a part of a DHGC. [ABSTRACT FROM AUTHOR]

One of the challenges with the dynamic inductive power transfer (DIPT) technique is the electric vehicle detection (EVD) that helps the DIPT system to control the power supply of the transmitter. The EVD method applying auxiliary coils is a promising candidate because the flat shape of the auxiliary coils is suitable for the compact design. However, the EVD may fail when the metallic foreign object (MFO) is present. Therefore, the desire emerges in the integration design of the EVD and foreign object detection (FOD). The FOD can ensure the reliability of the EVD as well as the highly efficient operation of the DIPT system without MFOs. In this context, this paper proposes an integrated solution to the EVD and FOD well suited for DIPT systems. The integrated solution utilizes both passive coil sets (PCSs) and active coil sets (ACSs). Additionally, a novel detection resonant circuit (DRC) is proposed to realize EVD and FOD using the same coil sets and to amplify the measurement sensitivity. The operation mechanisms, the detection coil sets architecture, the design of the proposed resonant circuits and the detection procedure are detailed. Finally, a printed circuit board based prototype is built to validate the integrated functionality of the EVD and FOD in a DIPT prototype processing 1 kW output. Experiments considering the practical DIPT application scenarios are conducted, and the proposed detection method is able to achieve advantageously high sensitivity and no blind zone. [ABSTRACT FROM AUTHOR]

HL-2M is a middle-sized copper conductor tokamak, which aims to operate close-burning and high-performance plasma for experimental magnetic fusion researches. The magnetic field coil system is an important part of HL-2M machine, consisting of a toroidal field (TF) coil system and a poloidal field (PF) coil system. In the operation of HL-2M, the TF coils operate in the environment of high current, strong magnetic field, and high stress. The structure, electromagnetic, electrical and thermal issues of TF coils were solved in design and construction phase. In this paper, the structure design principle of the demountable TF coils including some key components, was introduced, and then the construction of the TF coils, especially the industry processing, was established. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a variable protective resistor that realizes controllable energy dissipation and temperature inhibition for the no-insulation (NI) HTS coil-systems, during sudden discharging. The resistor is paralleled with the meter-class bore NI coil, which aims to be used in a high-field magnetic resonance imaging scanner (MRI), to avoid burn-out and shorten restart time of the coil when it has to be shut-down during an accident. To establish the relationship between the value of protective resistor, the energy dissipation and the temperature increase during sudden discharging for the NI coil, in this study, a numerical analysis coupled with a partial element equivalent circuit and a thermal analysis was conducted. Based on the results, the mechanism that how a protective resistor shares energy dissipation and inhibits temperature increase, has been clarified. Meanwhile, the effects of the value of protective resistor on the discharging behavior and temperature increase of NI pancake coil during sudden discharging, were also evaluated to verify the feasibility of this protection method in the application of MRI. [ABSTRACT FROM AUTHOR]