Eddy Current Effects Research Articles

A Duality Based Quasi-Steady-State Model of Three-Phase Five-Limb Sen Transformer

A three-phase five-limb transformer is a potential application form of the Sen Transformer (ST), especially for the scenarios with significantly unbalanced load conditions. This paper proposes a quasi-steady-state model of three-phase five-limb ST (TPFLST) based on duality. Firstly, an equivalent circuit model that takes into account the eddy current effect and the coupling effect involving the magnetic circuit can be derived according to the equivalent magnetic circuit of the TPFLST. The iron-core of the TPFLST may be represented by the parallel combination of the resistances reflecting the power loss of the iron-core and the saturable inductances considering the ferromagnetic hysteresis in virtue of the principle of duality. Subsequently, an electric circuit model of the voltage and current of each winding for the TPFLST is able to be accomplished on the basis of the electrical connection between the TPFLST and the external systems in accordance with Kirchhoff’s voltage and current law. Consequently, a quasi-steady-state model of the TPFLST which considers the coupling relationship involving the magnetic and electric circuits can be formed by combining the equivalent circuit model and the electric circuit model. With the help of MATLAB, the effectiveness of the proposed model may be verified by comparing the results about power flow control including power, voltage, and current with the ones from the existing literature. Furthermore, the TPFLST is found to be better-suited for the unbalanced load condition according to a comparison among the unbalanced degrees of output currents for the STs with different core structures under unbalanced load conditions.

Opportunities and challenges in microwave absorption of nickel-carbon composites.

In recent years, the problem of electromagnetic wave (EMW) pollution has attracted more and more attention with the development of science and technology. In order to solve this complex problem, the research and development of EMW-absorbing materials is crucial. The new absorbing materials should have the characteristics of light weight, high efficiency, wide bandwidth, environmental protection, oxidation resistance, and other characteristics. Traditional single-phase Ni materials exhibit remarkable ferromagnetic behavior and double-loss mechanisms (dielectric loss and magnetic loss), and are considered as efficient EMW absorbers. However, under the action of EMWs, especially in the GHz frequency band, Ni materials tend to produce an eddy current effect, which limits their application prospects. For Ni-based materials, there is much interest in modifying the composite materials by designing a hierarchical structure for their preparation. Traditional, single-phase, carbon-based materials have been widely used in related fields because of their light weight and good conductivity. However, a single-loss mechanism will affect the impedance matching of carbon materials, thus affecting their application in the field of absorbing waves. For carbon materials, people use them as a filler or matrix material to fabricate composites with metals, metal oxides, or polymer materials to obtain carbon-containing absorbing materials. This paper reviews the evaluation and design principles of the absorbing properties of EMW-absorbing materials. Then, the progress of modified single-phase Ni-based materials (designed materials with 0D, 1D, 2D, and 3D structures), the development of carbon materials (carbon black, carbon nanotubes, carbon fiber, graphite oxide, reduced graphene oxide, and biomedical carbon), and the research progress of Ni-C composite materials (the composite material formed by nickel and carbon) are reviewed. The ultimate goal is to obtain absorbers with light weight, strong absorbing ability, and a wide frequency band. In particular, Ni-MXene, Ni-biomedical carbon, and Ni-multiphase carbon composites are the target direction for designing new and high efficiency EMW absorbers. Finally, the basic challenges and opportunities in this field are discussed.

Distinguishment between contributions of deformation and eddy current effects to compressive impedance responses of intrinsic flexible coil

The impedance of the intrinsic flexible coil (composed of the conductive fillers and the polymer matrix) is sensitive to the deformation of the coil in the compression phase and the distance between the coil and the metallic target in the approaching phase, which indicates that the intrinsic flexible coil has the potential to be used as the deformation/distance sensor. The impedance response of the coil to the compression (i.e. compressive impedance responses) is induced by not only the deformation effect but also the eddy current effect, which complicates the analyses on the sensing properties of the coil. To distinguish the compressive impedance responses induced by the aforementioned two effects, the experiments under the conditions of the nonmetallic and metallic targets are designed. Under the condition of the nonmetallic target, the deformation raises the impedance amplitude and reduces the impedance angle in the compression phase, and there is no change in the impedance in the approaching phase. Under the condition of the metallic target, the impedance amplitude is raised and the impedance angle is reduced with the decrease/increase of the distance/deformation in the approaching/compression phase. The change in the normalized impedance during the compression under the condition of the metallic target is far more than that under the condition of the nonmetallic target, indicating that the contribution of the eddy current effect to the compressive impedance response is dominant over the deformation effect.

Numerical Simulation and Experimental Analysis of the Magnetic Damping Effect generated by a Moving Magnet

Nowadays, to reduce vibrations of machines, damping devices utilize the eddy current damping ef-fect being increasingly investigated for its advantages of no mechanical contact, no viscous liquid required, high reliability, and good damping capacity. This article studied the main principle of the eddy current damping effect for a moving permanent magnet in a stationary and electrically conduc-tive nonmagnetic cylindrical tube. The magnetic damping coefficient is investigated experimentally, analytically, and by numerical simulations in a steady-state. The numerical simulation is performed in the ANSYS Maxwell programme. The obtained results indicate that the damping force affecting the moving magnet has a viscous form. The experimentally measured and computed results are in good agreement. The effect of varying tube diameter and the tube wall thickness on the magnetic damping coefficient is shown. The contribution of this article consists in the development and a comparison of the obtained results of three approaches for determining the magnetic damping coefficient for a mov-ing magnet in a cylindrical tube.

Motion induced eddy current based testing method for the detection of circumferential defects under circumferential magnetization

Magnetic flux leakage (MFL) testing is widely applied in the online detection of steel pipes. Different magnetizing directions are required for the detection of defects in different directions. As the speed of online MFL testing increases, the motion induced eddy current (MIEC) effect becomes significant, and the direction of the MIEC is perpendicular to defects in the same direction as the magnetization. Therefore, the magnetic field signal generated by the MIEC perturbation is analyzed by simulation and compared with MFL signal. It is found that the amplitude of the magnetic field signal generated by the MIEC perturbation increases with the rise of the rotational speed and magnetization. In high rotational speed and strong magnetization, the amplitude of the magnetic field signal caused by MIEC perturbation is greater relative to the amplitude of the MFL signal, providing a possibility for detecting defects that are parallel to the direction of magnetization.

Sinopticheskiye vikhri otkrytogo okeana: obzor eksperimental'nykh issledovaniy

The paper is aimed at reviewing the studies of mesoscale eddies in the open ocean carried out by the Soviet and foreign institutions during the experiments in the specified geographical regions. The eddy-current effects are known since the 1930ies, and just the experiments “Polygon-67” in the Arabian Sea, “Polygon-70”, MODE , POLYMODE, Tourbillon , “Mesopolygon” in the tropical Atlantic, “Megapolygon” in the northwestern Pacific Ocean have advanced our knowledge about physical nature of the ocean eddy dynamics. Long-term complex measurements including current meters at the moored buoy arrays accompanied by a series of hydrographic surveys have provided the required experimental data for developing the theory of mesoscale variability. It explained arising and evolution of the eddies in the ocean as a result of interaction between various physical processes: baroclinic instability of a large-scale current, transformation of geostrophic turbulence in the Rossby wave field, barotropization of eddies and others. Later on, the studies of the ocean mesoscale variability evolved from the oceanographic surveys and special-purpose experiments at the polygons performed due to the research vessel cruises to the satellite altimetry methods and the drifter technologies. All the modern global estimates of eddy formations published in the last decade confirm the previous summaries, particularly those describing spatial distribution of the eddy kinetic energy in the World Ocean. They also represent new or the improved assessments of the eddies’ various characteristics: their size, drift velocity and direction, sign of rotation, nonlinearity, trajectory shear and others. Despite of the progress in remote sensing and regular launching of great amount of drifters and profiling floats, it is still difficult to obtain a comprehensive pattern of eddy dynamics within the whole World Ocean. It seems perspective to resume in future special-purpose experiments in the key regions of the World Ocean based on modern technologies.

An Eddy Current-Based Structural Health Monitoring Technique for Tracking Bolt Cracking.

Bolted joints are the primary structures for the load transfer of large-scale structures. It is vital to monitor the process of bolt cracking for enduring structural safety. In this paper, a structural health monitoring technique based on the embedding eddy current sensing film has been proposed to quantify the crack parameters of bolt cracking. Two configurations of the sensing film containing one-dimensional circumferential coil array and two-dimensional coil array are designed and verified to have the ability to identify three crack parameters: the crack angle, the crack depth, and the crack location in the axial direction of the bolt. The finite element method has been employed not only to verify the capacity of the sensing film, but also to investigate the interaction between the crack and the eddy current/magnetic field. It has been demonstrated that as the crack propagates, the variations of the induced voltage of the sensing coils are influenced by both eddy current effect and magnetic flux leakage, which play different roles in the different periods of the crack propagation. Experiments have been performed to verify the effectiveness and feasibility of the sensing film to quantify three crack parameters in the process of the bolt cracking.

Study on Au coating of ceramic-lined thin-wall vacuum chamber for HIAF

HIAF-BRing, the main synchrotron accelerator of the High Intensity Heavy-Ion Accelerator Facility, requires an average pressure lower than 1 × 10−9 Pa and the magnetic field increase rate no less than 12 T/s to fulfill radioactive beam physics and high energy density physics experiments. To reduce the eddy current effect and the gap size of dipoles compared to the thin-wall stainless steel vacuum chamber with reinforced ribs, a new design of ceramic-lined vacuum chamber with wall thickness 0.3 mm has been proposed by IMP. In order to effectively reduce the beam impedance and the desorption rate of ceramic materials, Au coating on ceramic (Yttria stabilized zirconia) by magnetron sputtering has been carried out. The adhesive force of Au film is 28.1 MPa measured by scratch test while the crystalline size of Au particle is in the range of 15.7–21.4 nm by X-ray diffraction (XRD). The longitudinal impedances of four types of round-ring-lined 0.6-m-long straight stainless-steel tubes and the ultimate pressure of the new designed vacuum chamber (uncoated vs Au-coated) have been measured to verify the feasibility of this method.

Time-Domain Finite-Element Eddy-Current Homogenization of Windings Using Foster Networks and Recursive Convolution

In this article, we propose an alternative time-domain approach for the homogenization of multiturn windings with frequency-dependent parameters in finite-element (FE) models. First, an elementary 2-D FE characterization of the conductors is carried out over the frequency range of interest to obtain the frequency-dependent parameters and account for the eddy-current effects in the winding. These complex coefficients are subsequently associated with an equivalent Foster network and translated into the time domain via the inverse Laplace transform. The resulting time-domain equations are solved with a recursive convolution scheme. No extra degrees of freedom are required in the homogenized winding. The results of the homogenized model present an excellent agreement with those obtained by an accurate but expensive FE model in which all turns are explicitly discretized. The proposed approach is further compared with a previously developed time-domain homogenization technique based on RL Cauer networks.

Finite-element/boundary-element transient modelling of hysteresis motors

This paper presents a transient study of hysteresis motor based on the proposed hybrid method of finite element method- boundary element method (FEM-BEM) in which the Jiles-Atherton (J-A) vector hysteresis model of the hard-magnetic material of the rotor is incorporated. The air–gap region is modeled by BEM in order to avoid the discontinuity in the FEM equations due to J-A hysteresis model and the rotor movement and, therefore, the eddy current effect is taken into account in the rotor part, for the first time. To the best of the author’s knowledge, the prior time-dependent numerical models have ignored the torque component caused by eddy currents in the rotor of hysteresis motor, due to difficulty in rotating the mesh in the rotor region and the related convergence problems. The proposed model is employed to study the phenomenon of short period over-excitation in hysteresis motors. A comparison is done between the proposed time-domain model and the frequency-domain finite element model of the hysteresis motor.

An unbiased method for PRF-shift temperature measurements in convective heat transfer systems with functional parts made of metal

The purpose of this study is to provide a PRF-shift method for fluid temperature measurements in convective heat transfer systems, which contain functional parts made of metal. Such measurements are extremely useful to examine and design convective cooling systems for industrial devices. Metals like copper seem inevitable for such applications because no commonly available non-metallic material reaches the same level of thermal conductivity as for example copper. In MRI, electrically conductive parts embedded in the measured sample are known to produce various kinds of errors including errors in the image phase caused by eddy currents. Two methods are compared that can be used to remove the eddy currents induced phase: via the phase difference of two readouts at different echo times and via the sum of the phase of two acquisitions with reverse gradient polarity and same echo time. The latter method, termed Rot-Echo, provides a better measurement efficiency because of higher temperature sensitivity. Also, this technique is able to directly measure the eddy currents induced phase map. After verification in a stationary water experiment, the Rot-Echo method was applied to time-averaged temperature measurements in a Pin Fin heat exchanger, comprised of water flow that is heated by an array of copper pins. The temperature fields acquired in the Pin Fin heat exchanger under stable thermal-hydraulic conditions agreed well with data from temperature sensors. No eddy currents effects were visible in any of the data sets in the vicinity of the copper rods. In conclusion, this study shows that unbiased PRF-shift temperature measurements are feasible in complex flow systems even if metallic material is used for the functional parts.

Design and indirect adaptive fuzzy H∞ control of a novel retarder coupled with eddy current effect and MR effect

To improve the poor braking performance of the traditional eddy current retarder, a novel retarder is developed by coupling the eddy current effect and the magnetorheological effect, which has large torque at low speed and stable torque at high speed. To meet the constant speed requirement in the braking process, the indirect adaptive fuzzy H∞ control strategy is employed to control the rotor speed of the designed retarder. The results show that the proposed retarder has the characteristics of continuously adjustable large torque in full speed section, sensitive control process and constant speed intelligent control.

Research on Absolute Positioning Sensor Based on Eddy Current Reflection for High-Speed Maglev Train.

A novel absolute positioning sensor for high-speed maglev train based on eddy current effect is studied in this paper. The sensor is designed with photoelectric switch and four groups of unilateral coplanar code-reading detection coil combination. The photoelectric switch realizes the positioning of the marker plate, and the four groups of detection coils read the mileage code of the mileage sign plate to obtain the absolute mileage information of the vehicle, which effectively reduces the quality and volume of the sensor, and reduces the impact of ice and snow. At the same time, the code-reading reliability and speed adaptability index are proposed. The code-reading reliability of the sensor is analyzed and tested under the fluctuation of levitation guidance, and the positioning error under the speed range of 0–600 km/h is calculated and analyzed. The results show that the novel sensor has the advantages of simple and compact structure. It still satisfies the system’s requirements for absolute vehicle mileage information under the conditions of vehicle operating attitude fluctuations and changes in the full operating speed range.

A model for calculating losses in transformer related to orders and harmonic amplitude under analysis of joule effect, eddy current and hysteresis

AbstractThe electrical transformer is one of the most used equipment in electrical power systems. The non-linear electrical loads are increasing, mainly in the electrical distribution system, and the electrical power transformer is inserted in this scenario, supplying these loads. Consequently, the increasing non-linear loads affect the electrical transformers and their factors directly, like in the dependency between temperature and harmonic increase. Therefore, to study the influence of harmonics in the transformer’s temperature, one should understand how it will behave with these changes in the electrical power system. For this reason, in this article, numeric simulations and tests were performed to predict the transformer temperature behavior. The proposal is a numeric technique for coupling two equations, thermal and electromagnetic, of an electrical transformer, considering heat sources regarding joule, eddy current, and hysteresis effect. To evaluate the numeric simulation and understanding the electrical transformer behavior in real-life, tests with specific harmonic orders (3rd, 5th, and 7th) and their combinations and a test with less than 10% total harmonic distortion, according to IEEE 519 standard were performed. It is verified that the electrical transformer temperature rises with the increase in harmonic amplitude and its orders. Results show that the industry must be aware of the effects of the increasing non-linear loads when designing the next generation of transformers concerning their durability and lifetime.

A Mathematical Model of a Collector Traction Motor with Separate Consideration of Eddy Currents of the Main and Additional Poles

A mathematical model of a collector traction motor with independent excitation has been proposed in which eddy currents from the main and additional poles are separately taken into account. The results of computer simulations to determine the response of developed model to an abrupt change in the voltage across the anchor and when the anchor is powered by a pulse converter have been considered. The electromagnetic processes that occur in the traction motor have been examined in detail at rated and reduced current of main poles and at various speeds. The mechanism of the effect of eddy currents from additional poles on the magnetic flux of main poles of the machine, emf, and rate of rise of the anchor current has been analyzed. The factors directly affecting the degree of influence of eddy currents from additional poles on the electromagnetic processes in a traction motor have been determined. Conclusions have been drawn regarding the appropriateness of taking into account the phenomenon under consideration when simulating the operation of a traction electric drive.

Computerized measuring system for study of aluminum alloy defects

The hardware-software complex which allows carrying out defect detection in materials based on various aluminum alloys was developed using a transducer based on eddy current effects. The hardware-software complex included the developed software coded in C++. A digital displacement transducer operated by an Arduino microcontroller has been designed, which can automatically move the transducer over a test object. In order to test the system operability, a series of scans of plates made of duralumin and aluminum-magnesium alloys with knowingly existing internal defects in the form of cuts imitating the presence of cracks in the metal and located at depths from 1 to 5.5 mm was made. This paper provides information illustrating the correlations between the system response to a 700 Hz signal and the presence of internal material defects. The eddy-current transducer exciting winding signal frequency exerts significant influence on this process, and this has been also demonstrated in the study.

Optimized Portable Unilateral Magnetic Resonance Sensor for Assessing the Aging Status of Silicon Rubber Insulators

Silicone rubber insulators (SRIs) play an important role in high-voltage power transmission lines. Given that SRIs critically threaten the safe operation of the power grid, quantitatively assessing the aging status of SRIs in situ is crucial. In this article, a portable unilateral magnetic resonance (UMR) sensor with a U-shaped magnet structure and its measuring circuit were designed for the nondestructive detection of the aging status of SRIs in situ. First, the optimization efficiency of the magnet structure was improved through a uniform design method. Then, the planar radio frequency (RF) coil was designed by the finite-element method. Furthermore, the demagnetization effect of eddy currents induced in metal materials on the RF magnetic field was analyzed. We measured the SRI sheds at different service times and obtained the corresponding 1H transverse relaxation decay curves by importing the Carr- Purcell-Meiboom-Gill (CPMG) sequence. Finally, the transverse relaxation decay curves were postprocessed using inverse Laplace transformation, and the 1-D spectrum distributions of transverse relaxation time (T2) were obtained. The results reveal that T2 of the surface of the SRI shed decreases as the service time of the SRI increases. In addition, the difference in T2 between the surface and interior of the SRI shed increases. The comparison experiments demonstrate that the U-shaped sensor designed in this article is superior to the curved sensor previously designed by our team. The effect of temperature variation on SRIs aging assessment was considered at last.

Design of novel CNT/RGO/ZIF-8 ternary hybrid structure for lightweight and highly effective microwave absorption

Carbon-nanotube-based composites are highly desirable for addressing the difficulties relevant to the quality of electromagnetic wave absorbers. The introduction of lightweight nanocomposites for constructing new structures has been widely studied due to the transformation in impedance matching and attenuation. In this paper, a novel carbon nanotube-graphene oxide-zeolitic imidazolate framework-8 (CNT/RGO/ZIF-8) ternary hybrid structure was successfully fabricated by a facile solvothermal process. The ZIF-8 was entangled initially by carbon nanotubes via the π–π interaction between organic ligands and benzene ring structure in CNT. Then, the CNT/ZIF-8 composite was immobilized on the surface of RGO by interacting with the active functional group of RGO. The structure and performance for CNT, CNT/ZIF-8, and CNT/RGO/ZIF-8 were compared to investigate the interaction mechanisms between components, and CNT/ZIF-8 exhibited a distinct improvement for microwave absorption performance. Furthermore, the introduction of RGO can accelerate the amelioration of absorption characteristics. The interfacial bonding between CNT, RGO, and ZIF-8 exerts a great influence on the absorbing quality. The mechanism of absorption of electromagnetic waves was explained by the synergistic effects of conduction loss, polarization behaviors, and eddy current. The unique structure could offer new insights to exploit advanced microwave-absorption materials.

Soft Inductive Tactile Sensor Using Flow-Channel Enclosing Liquid Metal

There are structural challenges in increasing the softness of conventional soft tactile sensors because rigid electrical elements have to be installed around the sensing areas, which should be compressive, stretchable, and durable. To solve these issues, we propose an inductive tactile sensor whose silicone-rubber body has only two liquid-metal reservoirs connected by an elongated flow channel. When one reservoir is placed around the sensing area, another one can be placed at a non-sensing area. Furthermore, in this structure, touch can be detected by monitoring the inflow and outflow of the liquid-metal in the latter reservoir by using a separately placed coil circuit based on the eddy-current effect. The proposed method requires no direct electrical connections with liquid metal in the reservoirs or flow channels. This means that the sensor body has no inhibitor that reduces its compressibility and stretchability, and that deteriorates its durability. The experimental results demonstrated that larger reservoir diameters provided larger sensitivity and higher signal-to-noise ratio of approximately 65 dB. Additionally, we observed that the bending of the body does not affect the sensor response as much as gravity. Therefore, we conclude that our sensor has structural advantages for tactile-sensor installation, especially in soft actuators, because our completely soft sensor does not experience reduction or deterioration in its functionality owing to its softness.

절삭 제동을 통한 추락 방지용 고속 안전 브레이크 설계

Free fall safety brakes against accidental cable failure such as in elevators may require friction, wedging action, eddy current, and other effects. An ideal safety brake system should be quick in its deployment with sufficient payload capacity in compact dimensions. In this study, a safety braking system with a quick deployment mechanism is proposed. The mechanism housed in a carrier is suspended by the cable and connected to the payload. At the onset of cable failure, a linkage system is driven by a pre-loaded spring to drive terminal cutting tools tips against the sacrificial braking pads on each side of the vertical track. Experiments showed that large braking force may be achieved by a compact mechanism. Several design issues of linkage deployment, braking force control, and drop dynamics are discussed.