Characteristics Of Coil Research Articles

A Study of Magnetic Coupling Characteristics of Dual Receiver Coil for Dynamic Wireless Power Transfer

For the problem of fluctuation of transmission power and load voltage between magnetically coupled mechanisms in the dynamic wireless power transfer (DWPT) system of the electric vehicles (EV), a magnetically coupled mechanism with dual receiving coils (R-C) of electric energy on the receiving side is proposed in this paper. The transmitting coils (T-C) are connected in parallel in a multi-stage manner flat on the road, and when the EV drives above a section of T-C, this T-C is energized to charge the EV. In the paper, the theoretical model of the circuit and the theoretical model of the magnetic circuit of the dual R-C magnetic coupling mechanism are first established. The feasibility of this structure is verified through the derivation and calculation of the working principle of the system. Finally, the simulation and experimental results verify the effectiveness of the coupling mechanism. The experimental results further demonstrate that the magnetically coupled structure with dual R-C can effectively reduce the power fluctuation during the T-C switching and reduce the laying of T-C to reduce the cost.

Research on Inductance–capacitance electromagnetic resonance measurement of prestressed concrete beam

Effective prestress change detection has a guiding effect on the safety of prestressed concrete structures. The measurement method of inductance–capacitance (LC) electromagnetic oscillation circuit can directly reflect the correlation between the stress of the steel strands and the electromagnetic resonance frequency. In this paper, the post-tensioned unbonded prestressed steel strands inside the structure are treated as a helical coil. Combined with the inductance characteristics of the helical coil in the resonance circuit and the characteristics of stress in the prestressed structure, the relationship between the load and the stress of the structure under vertical loading is analyzed. A function model of the stress and resonance frequency in the LC oscillation circuit is established. Then a 4.8 m long unbonded prestressed concrete beam is used for 0–55 kN vertical loading experiments and the electromagnetic resonance circuit is completed to detect the change of the resonance frequency increment of the steel strands with the measured stress increment. Theoretical analysis and experimental results show that the electromagnetic resonance circuit can effectively detect structural load stress changes that are positively related to the electromagnetic resonance frequency of the steel strands.

Numerical comparison study on heat transfer enhancement of different cross-section wire coils insert with varying pitches in a duct

Heat transfer enhancement (HTE) efforts spent during the last half-century have become one of the most important working areas of researchers from both academia and industry. One of the most popular passive methods, with regard to the price-performance ratio, is to place wire coils in a pipe or duct. In this study, the heat and pressure drop characteristics of diamond, triangular, and circular cross-sectional wire coils (DWC, TWC, and CWC) in a square duct were investigated by using the FLUENT program. In addition to the cross-section examination, the thermo-hydraulic behavior of three different pitches (p = 54, 72, and 90 mm) for the specified geometries were also investigated. The Reynolds number was between 4387 and 18,415. The square duct was 1.25 m in length, and was 18 mm in diameter. The results showed that the Nusselt number of CWC, TWC, and DWC were higher than that of a smooth pipe within 38–88%, 37–93%, and 38–98% range, respectively. The friction of CWC, TWC, and DWC was observed to be higher than that of a plain tube within a range of 87–278%, 82–266%, and 107–366%, respectively. The TWC with 90 mm pitch showed the highest heat transfer performance evaluation criteria (PEC) with a performance coefficient of 1.3 at Reynolds number of 4504, whereas the DWC with 54 mm pitch was observed to show the lowest PEC. Thus, the as-obtained PEC, which is 30% higher than that of a plain tube, indicates the prominence and effectiveness of the numerical study in increasing the heat transfer.

Capacity factor characteristics for a multi‐tubular sensible energy storage system with wire coil inserts

The transient energy storage in a sensible energy storage system (SESS) depends on the rate of energy stored in the system. The rate of energy stored in a sensible energy system is a strong function of spatial temperature distribution that governs the energy distribution in the storage medium. The present study explores the energy and capacity factor characteristics of a wire coil fitted multi-tubular SESS. A storage system is molded using M30 grade concrete of density 2200 kg/m3) and specific heat capacity 850 J/kg/K). The inlet temperature of the air, used as heat transfer fluid, is varied from 45°C to 75°C. The pitch to diameter (p/d) ratio of the wire coil insert is varied from 0.25 to 0.75 to examine its effect on energy storage/release and capacity factor. Using a (p/d) ratio of 0.5 for wire coil inserts, the maximum capacity factor of 0.98 is achieved during the charging phase of sensible energy storage at 55°C inlet air temperature and 0.029 kg/s mass flow rate of heat transfer fluid (HTF). With respect to the smooth SESS, the maximum improvement in capacity factor is found to be 29%.

Analysis and Experimental Research On Dynamic Characteristics of Operating Mechanism of Fast Vacuum Transfer Switch

The mathematical model of electromagnetic repulsion operating mechanism of fast vacuum transfer switch (FVTS) for 400 V/630 A/12.5 kA dual power supply system is proposed, and two-dimensional rotational symmetry model of electromagnetic field simulation is established in this paper. Taking the repulsion peak value, velocity characteristics and starting time as the design goals, through analysis and comparation of the dynamic characteristics of the double coil and the metal disc repulsion mechanism, the design scheme of the operating mechanism for the FVTS with short stroke and short opening time is realized. Based on the comparative study of simulation and experiment of vacuum transfer switch prototype with fast repulsion mechanism, the 5.5 mm stroke can be completed within 5ms under the operating condition of 320 V capacitor voltage and 8000 μF, which meets the engineering application requirements of fast switching for the sensitive load.

On the accuracy of Tier 4 simulations to predict RF heating of wire implants during magnetic resonance imaging at 1.5 T.

Magnetic Resonance Imaging (MRI) access remains conditional to patients with conductive medical implants, as RF heating generated around the implant during scanning may cause tissue burns. Experiments have been traditionally used to assess this heating, but they are time-consuming and expensive, and in many cases cannot faithfully replicate the in-vivo scenario. Alternatively, ISO TS 10974 outlines a four-tier RF heating assessment approach based on a combination of experiments and full-wave electromagnetic (EM) simulations with varying degrees of complexity. From these, Tier 4 approach relies entirely on EM simulations. There are, however, very few studies validating such numerical models against direct thermal measurements. In this work, we evaluated the agreement between simulated and measured RF heating around wire implants during RF exposure at 63.6 MHz (proton imaging at 1.5 T). Heating was assessed around wire implants with 25 unique trajectories within an ASTM phantom. The root mean square percentage error (RMSPE) of simulated vs. measured RF heating remained <1.6% despite the wide range of observed heating (0.2 °C-53 °C). Our results suggest that good agreement can be achieved between experiments and simulations as long as important experimental features such as characteristics of the MRI RF coil, implant's geometry, position, and trajectory, as well as electric and thermal properties of gel are closely mimicked in simulations.Clinical Relevance- This work validates the application of full-wave EM simulations for modeling and predicting RF heating of conductive wires in an MRI environment, providing researchers with a validated tool to assess MRI safety in patients with implants.

A numerical method for spatially-distributed transient simulation to replicate nonlinear ‘defect-irrelevant’ behaviors of no-insulation HTS coil

This paper presents a numerical method, based on the partial element equivalent circuit (PEEC) technique, for spatially-distributed and time-varying simulation to analyze nonlinear ‘defect-irrelevant’ behaviors of a no-insulation (NI) high temperature superconductor (HTS) coil. We suggest a resistivity parameterization approach in combination of the PEEC method to replicate electromagnetic dynamics of an NI HTS coil containing multiple ‘defects.’ The proposed method is adopted to investigate ‘defect-irrelevant’ behaviors of an NI single pancake coil having lap joints as a form of artificial defects. To validate our approach, electromagnetic characteristics of the NI test coil are measured in a bath of liquid nitrogen at 77 K and compared with four key simulation results: (a) local voltages; (b) current distribution; (c) magnetic field;and (d) Joule heating distribution. Experimental measurements of local voltages and the magnetic field are compared to the simulation results to validate our numerical method.

Numerical study on temperature rise and mechanical properties of winding in oil-immersed transformer

In the present paper, the electromagnetic-fluid-thermal-mechanical stress coupling process in an oil-immersed transformer is numerical studied with finite element method. The relationship between electromagnetic force and flux leakage, interaction of losses, temperature and oil flow, and the influence of electromagnetic force and temperature rise on mechanical characteristics of coil are carefully analyzed. Firstly, the leakage flux is mainly generated at the ends of coil and core corner end. The electromagnetic force of B-Phase low voltage coil is the highest due to the leakage flux superimposition caused by A-Phase and C-Phase coils and higher current on B-Phase low voltage coil itself. Secondly, the interaction between losses, temperature and oil flow is remarkable. Compared with the results as heat source is constant, the loss density of high and low voltage coil increased by 18.18% and 14.87%, respectively, and the hot spot temperature increased by 7.06 K. Finally, it is revealed that the coil deformation is mainly caused by thermal load, and little affected by electromagnetic force. The frequency of stress is twice as high as that of energized current. The stress at both ends of the coil is the highest and it would lead to fatigue failures.

Sharp demagnetization of closed-loop HTS coil in first cycle of external AC fields induced by unexpected dynamic resistance

Dynamic resistance leads to the demagnetization of high-T c superconducting (HTS) permanent magnets (such as closed-loop coils and tape stacks) when exposed to AC fields. This letter reports on the systematic study of an unexpected dynamic resistance occurring in first cycle AC field, which can be induced by any weak AC field—even below the threshold value ‘conventionally’ defined for generating dynamic resistance. This resistance is predicted by a critical-state analytical calculation, and its physical origin is shown to be from the asymmetrical flux penetration. Numerically, this resistance is verified, and simulated for a closed-loop HTS coil, showing a non-negligible demagnetization effect. Experimentally, the current decay (i.e. demagnetization) characteristics of a closed-loop HTS coil in a sufficient range of AC fields are measured. This resistance manifests itself in the closed-loop coil as a relatively sharp current decay in the first cycle of the applied field; this observation is in qualitative agreement with the simulation. A comparative experiment is performed to eliminate the contribution from the index loss or ‘conventional’ dynamic resistance that also possibly results in a greater demagnetization in the first cycle owing to the larger coil current. As the result, this unexpected dynamic resistance is verified. The unexpected, sharp demagnetization caused by this resistance might need to be considered when designing HTS closed-loop coil applications.

AC Loss Evaluation of a Superconducting Pancake Coil with Coated Conductors using an Extended A-V Formulation

In this study, an extended A-V formulation is used to determine the alternating current (AC) losses of a coil made of high temperature superconducting (HTS) tape. The current is the same at each turn by balancing the voltages of each turn. By this modification, this method can be applied in a wide application area. This method also provides the chance to determine the calculations at currents higher than the critical current values in a more stable way. The AC loss characteristics of the pancake coil are examined in detail by changing the current value and frequency. Also, the losses at individual turns (1st, 5th, and 10th) are presented. It was seen that the most outer and inner turns have higher losses than that of the other turns. The AC loss results obtained from the extended A-V formulation used in this study are compared with experimental and H-formulation-based results and are in good agreement. The frequency dependence of the pancake coil's loss is revealed at 5 frequency values. The results show that the loss is frequency and current amplitude dependent as expected. Similarly, the calculated losses for each frequency are in good agreement with that obtained from the H- formulation. The current distributions of a single tape and the entire coil are also presented, and all results are discussed in detail.

Efficiency-Optimized Design of PCB-Integrated Magnetorquers for CubeSats

CubeSats are miniature satellites used to carry experimental payloads into orbit, where it is often critical to precisely control their attitude. One way to do this is through the use of magnetorquers, which can be integrated into PCBs. This technique saves considerable space and capital when compared with more common torque-rod magnetorquer systems. Here we derive a method of analyzing different PCB-integrated magnetorquer geometries, parametrizing them such that the magnetic moment and efficiency are optimized. Furthermore, by modulating the trace width, the trace number, and other electrical characteristics of the magnetorquer coil, this paper optimizes the generated magnetic moment. Both constant voltage and constant current sources are analyzed as inputs. These optimizations are then simulated in COMSOL for multiple geometries, and it is found that there exists an optimal geometry, given a specified power dissipation. Simulations verify the general trend and maxima of these derivations, barring small, consistent re-scaling in the magnitude of the coil resistance. It is also found that these PCB-integrated magnetorquers provide a sufficient alternative to commercial coil magnetorquers - particularly in volume-restricted configurations. This study extends such analysis to larger CubeSat configurations, and finds that these larger implementations increase magnetorquer efficiency. Optimizations for common PCB-implementable geometries on small satellites are tabulated in the Appendix.

Quench Characteristics of a 2G ReBCO Roebel Cable Pancake Coil in External Fields Up to 8T

A pancake coil was wound with a length of ReBCO 2G Roebel cable consisting of 15 strands and studied in detail at different operating temperatures between 4.2 K and 77 K. The coil was impregnated with an epoxy resin and cooling achieved through conduction from current contacts. The critical current was measured with transport currents up to 1500 A and in an external axial field up to 8 T. Quench measurements were carried out following point-like disturbances initiated by a localised miniature heater embedded inside the coil. The different heat dissipation at the current contacts was dynamically controlled with axillary heaters to ensure the isothermal condition of the coil for the successive quench episodes. The minimum quench energy (MQE) was obtained at different temperatures, fields and load currents relative to the critical current. The present work is a substantive follow up of previous studies at 77 K in liquid nitrogen and in helium gas down to 60 K, where it has been established that the coil retained the critical current of the superconducting strand/cable and its quench behaviour was unaffected by the lateral cooling by the cryogen.

Thermal-quench behavior of non-insulated high-temperature superconducting (HTS) racetrack pancake coil with cooling channels through the epoxy surface

The high-temperature superconducting (HTS) racetrack pancake (RP) coil is recommended to be used as a field coil in rotating machines such as generators and motors. Epoxy impregnation is normally required in the field coil to protect it against mechanical stresses due to the variation in the magnetic field and to enhance its mechanical stability to withstand rotor vibrations. However, the thermal conductivity of epoxy is very low compared with that of HTS. Consequently, when quenching is induced in an epoxy-impregnated coil, the Joule heating is poorly dissipated outward because of the absence of thermal drain to dissipate the heat in liquid nitrogen (LN2), which damages the coil through heat accumulation. We designed cooling channels (pores) through the surface of an epoxy-impregnated coil to boost the circulation of LN2 in the coil during the cooling process and to improve the operation of the coil during quenching. In this study, cooling-down and quench tests were performed on the epoxy-impregnated RP coils to investigate the effect of cooling channel on the thermal-quench characteristics of the RP coils. Moreover, the minimum quench energy and normal-zone propagation velocity of the hotspot induced in the coils were discussed on the basis of the quench-test results.

Performance evaluation of helical coils as a passive heat transfer enhancement technique under flow condensation by use of entropy generation analysis

Current research focuses on the performance of helically coiled tubes as a passive heat transfer enhancement technique for R134a flow condensation from an entropy generation perspective. Similar to other enhancement techniques, helical coils, are accompanied by pressure drop as a penalty, diminishing their performance, so that these coils are of lower performance compared to straight tubes where the increase in entropy generation due to pressure drop overcomes the decrease in entropy generation due to enhanced heat transfer. Unlike previous studies that have largely investigated heat transfer and pressure drop characteristics of helical coils regardless of their performance, this study employs entropy generation analysis as an effective method to distinguish flow and geometrical conditions at which helical coils are of lower entropy, i.e. higher performance, compared to straight tubes. The findings reveal that, for both helical and straight tubes, entropy generation is enhanced as tube diameter, mass velocity, vapor quality, and wall heat flux increase and saturation temperature decreases. Additionally, applying helical coils within wider ranges of mass velocities can be justified at lower values of tube (≤8.3 mm) and coil diameters (≤200 mm), saturation temperatures (≤40 °C), and vapor quality (≤0.6), and at higher values of wall heat flux (≥15 kW/m2). These results substantiate that employing helical coils in lieu of straight tubes is not justifiable always (for all flow and geometrical conditions) although they are of superior heat transfer performance compared to straight tubes.

Recovery Characteristics of GdBCO Series-Connected Non-Inductive Coil in Pressurized Liquid Nitrogen for a Resistive SFCL

A SFCL (Superconducting Fault Current Limiter) is expected to limit a fault current and to improve system stability and operation flexibility in electric power system which is becoming more and more complicated and larger-scale. In order to put SFCL into practical use, it is important for quick recovery to improve the cooling property of a superconducting wire. Especially in resistive SFCL, the superconductor turns to the resistive state for current limiting performance, then the temperature of the superconductor rises up to the film boiling regime of LN2 heat transfer characteristics. After the fault, the SFCL should recover to the superconducting state (stand-by for repetitive fault) within a short period according to the circuit breaker operation. In this study, to improve current-limiting capability, we used GdBCO series-connected Non-inductive coil for the resistive SFCL and investigated the effect of different applying pressure for improvement of its recovery characteristics. In addition, we observed the difference of the boiling phenomena on the surface between under pressurized condition and under ambient pressure by a high-speed video camera.

Electrical Characteristics of HTS Coils With and Without Insulation in a Layer-Wound Configuration

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.

Multi-objective optimization of laminar flow characteristics in helical coiled tubes based on NSGA-II

To meet the requirement of energy conservation and optimize the design of helical coils in laminar flow, the pitch, the coil radius and the average inlet velocity were selected as design parameters to obtain the tendency of the heat transfer and flow resistance characteristics of the helical coils. Heat transfer coefficient and pressure drop per unit length of helical coils were taken as the optimization objective functions. A multi-objective optimization model was established, three candidate points A, B and C were obtained based on Non-dominated Sorted Genetic Algorithm-II (NSGA-II). The results showed that heat transfer coefficient and pressure drop per unit length increase with the pitch and inlet velocity whilst them decrease with coil radius, among which the influence of inlet velocity is the most obvious and the pitch is the least. It was found that the coil radius of most points in Pareto front was relatively concentrated. The comprehensive performance of candidate points A, B, C had been improved significantly by 16.3%, 28.3% and 19.6% respectively.

Inductive coupling characteristics of air-core toroid coil and its application in power line communication

Inductive coupling characteristics of air-core toroid coil and its application in power line communication

Thermal Characteristics of REBCO Coil in a Wireless Power Transmission System for the Railway Vehicle in Liquid Nitrogen

A wireless power transmission (WPT) system using the high temperature superconducting (HTS) coil for a railway vehicle is required to transmit the electric power of several hundred kW in a short time (60 s). In order to design the WPT system using HTS coil with the thermal stability, and it is necessary to clarify the thermal characteristics of the HTS coil at the operating current in kHz band and the operating conditions considering thermal stability in the WPT system. We analyzed the frequency characteristics of the critical current in the HTS coil above 1 kHz and investigated the operating conditions considering thermal stability in the WPT system for the railway vehicle using HTS coil in liquid nitrogen. As a result, the critical current of the HTS coil in the kHz band decreased with the frequency. This is because the AC loss in the HTS coil increased with the frequency, and the critical current density of the HTS coil decreased with increasing the surface temperature. In order to design the HTS coil with thermal stability in the kHz band, and it is necessary to operate the HTS coil on alternating current less than about 50% of the critical current measured by direct current. We found that the thermally stable WPT system capable of fast charging for 60 seconds can be realized by operating current at the frequency of about 2 kHz.

A mechanical analysis informed fractography study on load-specific fatigue behaviors of Pt–Ir coils used in implantable medical leads

Fatigue fracture is a major threaten to implantable medical coils such as platinum-iridium (Pt–Ir) coils used in deep brain stimulation leads. The fractography under bending and torsion fatigue was studied in comparison with mechanical analysis to grasp load-specific fatigue characteristics and understand the mechanisms. Mechanical analysis of the coil under bending and torsion was conducted with both analytical and numerical methods. Pt–Ir coils were experimentally fatigued at roughly paralleled bending and torsional load levels. The fatigue life was recorded and the fracture morphology was observed and analyzed. It is revealed that the helical structure of the coil turns bending and torsion loads into different locally distributed stresses, which mainly determine the fatigue behaviors. Features of fracture morphology, such as ratchet mark and fatigue striation, are identifiable to differentiate load types and stress levels. Both bending and torsion may play important roles in fatigue fractures of the coil. The study proposes an effective approach to study load-specific fatigue characteristics of medical coils which provides fundamental knowledge for medical lead design and clinical fracture diagnosis.