Eddy Current Density Distribution Research Articles

Aluminum Eddy Currents in PSRM Stator Arrays: Analysis and Mitigation for Improved Control Precision and Energy Efficiency

In this article, the influence of aluminum eddy currents in the PSRM stator array on electromagnetic properties and control performance is investigated. A model is developed to analyze the eddy current density distribution based on Maxwell’s equations, and an inductance model is derived that considers the eddy current effect. The effect of aluminum eddy currents on PSRM position control performance is qualitatively analyzed. The distribution of aluminum eddy currents and ohmic loss is verified through finite element analysis. The validity of the developed inductance model is experimentally verified. A material substitution method is proposed to eliminate the aluminum eddy current. Experimental results show that the position control accuracy of the PSRM prototype is improved by an average of 6.94% after the elimination of aluminum eddy currents, while the motor efficiency is improved by 6.51%.

Experimental study of different innovative measurement methodologies applied to a canned pulsed eddy current testing probe suitable for dilation measurement of test specimens

A compact pulsed eddy current testing probe is being developed for the online dilation measurement of test specimens, examined in the high-temperature environment of material testing reactors. The probe has to be canned with metallic clad to protect it from the corrosive sodium-potassium coolant medium present in the material testing reactor. Electromagnetic modelling of the probe was carried out to compute the distribution of time-dependent eddy current density in the vicinity of the probe. It is understood that the slope of the pulsed eddy current signals in the specific time zone where the lift-off point of intersection occurs show a good correlation to the distance between the face of the probe and the test specimen. This paper discusses the experimental study of employing different measurement methodologies at room temperature with the canned pulsed eddy current probe to evaluate its feasibility for dilation measurement. It is observed that a phenomenon of a divergence of signals, akin to the lift-off point of intersection, occurs just after the transient part of the pulsed eddy current signals. Slope analysis of these diverging pulsed eddy current signals was carried out for characterisation of the probe in the air medium as well as the metallic medium present in the gap between the probe face and the test specimen.

Theoretical essentials for designing viscous liquid pumping systems in the conditions of the Arctic region

The purpose is the creation of a scientifically based solution for the design of hermetic electromechanical converters adapted to existing pipelines, as well as those under construction and development. These pipelines meet the energy efficiency requirements and operate in the conditions of the Arctic region. Methods: methods of mathematical analysis, numerical methods, and methods of mathematical programming were used as the main mathematical means. The CFD design package of Ansys Maxwell was used. Research results: we showed that an increase of the efficiency of the system of technological transportation of petroleum products at low temperatures is possible through the use of electromechanical devices that combine the functions of heating and pumping the working liquid. We solved the field problem based on the analytical calculations carried out by a computer. This allowed us to determine the distribution of eddy current density in the structural elements of these devices responsible for creating pressure and heating the pumped petroleum products. The importance of the electrical parameters of the secondary windings has been confirmed numerically and experimentally. The hydraulic characteristics, mechanical losses, volumetric losses and efficiency are determined. Taking into account the outcomes of theoretical studies the experimental sample of the sealed electromechanical converter with the specified physical and chemical characteristics was created at Emperor Alexander I St. Petersburg State Transport University. Practical relevance: the obtained analytical formulas can be used at the development of the systems for pumping viscous liquids at low temperatures using the sealed electromechanical converters which helps to reduce the installed power of energy equipment without degrading the values of technological indicators.

Applicability of eddy current testing in CFRP using electrodes on CFRP surface and control of the testing range

In this study, a novel eddy current testing (ECT) method was developed to facilitate the testing of unidirectional carbon fiber reinforced plastic (UD-CFRP) and control the detection range. First, the effect of adding electrodes orthogonal to the fibers of UD-CFRP were analyzed. The results showed that the eddy current density could be significantly increased by adding electrodes. Moreover, it was found that the distribution of eddy current density in depth axis can be controlled by adjusting the distance of electrodes. Next, the same analysis was conducted for quasi-isotropic CFRP for comparison. The results showed that, unlike the results for the UD-CFRP, the distribution in depth direction could not be controlled by adjusting the distance of the electrodes. Finally, the impedance of the UD-CFRP with electrodes was measured, for confirming that adding electrodes facilitated ECT. It was also confirmed that the impedance increased as the distance between electrodes increased, and this trend was consistent with the numerical simulation results.

Design optimization of APMEC using chaos multi-objective particle swarm optimization algorithm

In order to meet the requirement that the permanent magnet eddy current coupler has larger output torque and smaller eddy current loss in actual operation, the structural parameters and operation performance of axial permanent magnet eddy current coupler (APMEC) are optimized by chaos multi-objective particle swarm optimization algorithm (CMOPSO) in this paper. The model of APMEC is established by three-dimensional finite element simulation. The central composite design (CCD) method is used to select the appropriate test point, and the response value is obtained by ANSYS finite element analysis software simulation. The second-order response surface regression model of APMEC was established according to the response value. The CMOPSO is used to optimize APMEC, and the optimal combination of structural parameters is obtained. By comparing the eddy current density distribution of APMEC before and after optimization with the finite element simulation experiment, it is verified that the optimization method is feasible to optimize the structural parameters of APMEC. The optimization results show that the efficiency of the permanent magnet eddy current coupler is more than 94%, and the energy consumption is reduced to 83% of the original energy consumption.

Design Method of Multiwavelength EMATs Based on Spatial Domain Harmonic Control.

Conventional electromagnetic acoustic transducers (EMATs) are generally only used to generate and detect guided waves with a single wavelength, which increases their sensitivity at that particular wavelength but limits their application scenarios and the accuracy of defect assessment. This article proposes a design method for multiwavelength EMATs based on spatial-domain harmonic control. First, the EMAT model is analyzed, where it is then outlined that the eddy-current density distribution of the specimen is equivalent to the spatial low-pass filtering of the coil-current density distribution. This shows that the multiwavelength guided waves can be achieved as long as the spatial distribution of the coil-current density contains those multiple harmonics that are desired. It is then proposed that the structure of the EMAT coil is equivalent to the spatial sampled pulse sequences of a spatial signal. The coil parameter design based on pulse modulation technology is proposed. Taking a dual-wavelength EMAT design for Lamb waves as an example, details of the coil parameter design are presented. The simulation and experiment with the dual-wavelength EMAT proved the correctness of the proposed method. Finally, an experiment with a three-wavelength EMAT demonstrated the feasibility of the proposed method in designing multiwavelength EMATs.

СИНТЕЗ ВИХРОСТРУМОВИХ ПЕРЕТВОРЮВАЧІВ З ОБ’ЄМНОЮ СТРУКТУРОЮ СИСТЕМИ ЗБУДЖЕННЯ, ЩО РЕАЛІЗУЄ ОДНОРІДНУ ЧУТЛИВІСТЬ В ЗОНІ КОНТРОЛЮ

A method for nonlinear surrogate synthesis of surface eddy current probes with a volumetric structure of the excitation system was proposed. This method a priori provides a given uniform distribution of eddy current density in the testing object area where the measuring coil is located. The implementation of the task using modern metaeuristic stochastic algorithms for finding the global extremum was achieved. For the effective usage of such algorithms, taking into account the effect of velocity, metamodels of eddy current probe were preliminarily created. They were built using a productive approximation technique based on artificial radial-basis neural networks with a Gaussian activation function. Acceptable accuracy of metamodels was achieved due to the simultaneous application of the search area decomposition technologies and plural neural networks based on the techniques of associative machines with group methods for obtaining a solution. For metamodels creation a multidimensional computer experiment design with high homogeneity was used on the basis of the parameterless additive Rd-Kronecker sequence. Numerical experiments to determine the eddy current density distributions which formed by synthesized excitation structures were carried out. The advantages of using a three-dimensional structure excitation system in comparison with classical and planar ones in terms of increasing the width of the testing zone, which is characterized by uniform sensitivity, were shown. Examples of practical implementation of an excitation system with a volumetric structure for an surface eddy current probe are given. References 13, figures 8, table 1.

Improving Flaw Detection through Integration of a Novel Eddy Current Probe with Fluxgate Magnetic Sensor

The objective of this study is to improve the detection capability of eddy current testing by developing a novel eddy current probe. The developed probe is composed of six excitation coils made at different areas and suitably aligned with a single-axis sensitive DRV425EVM fluxgate sensor. The distribution of magnetic field intensity and eddy current density of the developed probe were calculated using ANSYS 2019R3 (Maxwell-3D) simulation software. The simulation results revealed that the new probe design enhances the detection capability and the spatial resolution compared to the conventional design that uses a double-D coil. Experiments were carried out using the double-D coil as reference, under the same input parameter to detect flaws with various sizes and locations. The experimental results validated the simulation results and showed that the sensitivity and spatial resolution of the developed sensor are much better than those obtained by the conventional probe.

The Influence and Compensation Method of Eccentricity for Cylindrical Specimens in Eddy Current Displacement Measurement.

The eddy current displacement sensor (ECDS) is used to realize the precise detection of the rotor radial position in the magnetic suspension motor. The eccentricity between the probe axis and the measured surface normal reduces the measurement accuracy. An ECDS mathematical model is established to analyze the influence of the measured surface curvature and eccentricity on detection results. The eddy current density distribution law of the measured surface is obtained by using the finite element method (FEM). The experimental platform is set up based on the practical engineering structure, which contains two kinds structures of the single probe and the differential. The compensation method is introduced to reduce the error caused by the eccentricity. The displacement measurement error with and without compensation are tested separately. The results show that the largest full-scale error is less than 0.8% after compensation in the single probe structure, and 0.6% in the differential structure. For the engineering application, the orthogonal direction measured value is used as the eccentricity, and the compensation order of big then small is proposed. It is thus proved that the compensation method provides a guarantee for accurate feedback and control of the rotor radial position in the magnetic suspension motor system.

Modeling Magnetic, Electric, and Acoustic Fields of a Pass-Through Transducer When Testing Cylindrical Objects

We present results of numerically modeling the magnetic, electric, and acoustic fields of a pass-through EMA transducer of longitudinal waves by the finite element method in the COMSOL Multiphysics software environment. The main approaches used in the modeling are described. The influence of structural gaps between the EMA transducer and the test object on the magnitude and distribution of eddy current density, as well as the main and interfering components of a bias field have been investigated. The influence of operating frequency on acoustic field parameters has been analyzed. Recommendations are given on the choice of transducer’s operating frequency and probing-pulse quality factor needed to shape the required diagram of displacements relative to the object diameter and to assess the sensitivity to surface and internal defects located at different depths.

Studying the computational resource demands of mathematical models for moving surface eddy current probes for synthesis problems

Distribution of eddy current density for three types of coils of excitation of moving surface eddy current probes, in particular circular, rectangular, orthogonal-rectangular shapes was calculated according to the formulas of exact electrodynamic mathematical models with allowance for the speed effect. Calculation time from 8 to 20 hours was established for a circular excitation coil with dimensions of testing zone 50´50 mm at speed u x =40 m/s. The calculation time was from 8 to 9 hours for a rectangular excitation coil at a speed of movement in direction of two components u x , u y =20 m/s with the testing zone dimensions of 80´48 mm. The calculation time was more than 7 hours for an excitation coil of orthogonal rectangular shape with dimensions of the testing zone of 15´35 mm at a speed of movement in direction of components u x , u y =40 m/s; and for the testing zone dimensions of 12´24 mm for u x , u y =40 m/s it was longer than 9 hours. It was found that the computational complexity of calculation of distribution of the eddy current density with the use of exact mathematical models was rather large when changing even two spatial coordinates in the testing zone. That is, the direct use of exact mathematical models when calculating the values of distribution of the eddy currents density in the points of the controlled zone is inappropriate taking into account the considerable resource intensity of the computational process. The necessity for using a mathematical apparatus of surrogate optimization was substantiated for designing eddy current probes with a uniform distribution of eddy current density in the testing zone. This study is useful for non-destructive testing specialists in the field of mechanical engineering. The study results can be used in designing eddy current probes with improved metrological characteristics, in particular homogeneous sensitivity, localization of the probing excitation field, improved noise immunity, possibility of eliminating the edge effect manifestations in testing

Induced Current Magnetic Resonance Electrical Conductivity Imaging With Oscillating Gradients.

In this paper, induced current magnetic resonance electrical impedance tomography (ICMREIT) by means of current induction due to time-varying gradient fields of magnetic resonance imaging (MRI) systems is proposed. Eddy current and secondary magnetic flux density distributions are calculated for a numerical model composed of a z-gradient coil and a cylindrical conductor. An MRI pulse sequence is developed for the experimental evaluation of ICMREIT on a 3T MRI scanner. A relationship between the secondary magnetic flux density and the low-frequency (LF) MR phase is formulated. Characteristics of the LF phase, the eddy current, and the reconstructed conductivity distributions based on the simulated and the physical measurements are in agreement. Geometric shifts, which may contaminate the LF phase measurements, are not observed in the MR magnitude images. Low sensitivity of the LF phase measurements is a major limitation of ICMREIT towards clinical applications. The reconstructed conductivity images are rough estimates of true conductivity distribution of the experimental phantoms. Although the experimental results show that ICMREIT is safe and potentially applicable, its measurement sensitivity and reconstruction accuracy need to be optimized in order to improve the technique towards clinical applications.

Analysis of Secondary Losses and Efficiency in Linear Induction Motors With Composite Secondary Based on Space Harmonic Method

This study investigates the influence of the composite secondary with the solid and laminated back iron on the thrust, vertical force, secondary losses and efficiency in the prototype single-sided linear induction motor for metro by space harmonic method. First, a 3-D space harmonic analytical model, which can consider the skin effects, secondary constructions as well as end and edge effects, is proposed. Second, the air-gap flux and secondary eddy current density distributions along longitudinal and transverse directions are presented. Then, variations of secondary losses and efficiency with a specific number of secondary back iron laminations are comprehensively compared in the full slip, and the optimal number of laminations is obtained. Third, the propulsive and vertical forces are analytically calculated under full slip, and the efficiency in a range of rated speed is presented. Finally, these results are verified by measurements on an experimental rig of the linear motor.

Influence factors to affect eddy current loss of damper winding in 24 MW bulb tubular turbine generator

PurposeThe purpose of this study is to find out the influence degree of harmonic current on the generator operating parameters. In practical operation of the salient-pole synchronous generator, the heat generated by eddy current loss may lead to the breaking of damper winding, and the damper winding is a key component for ensuring the reliable operation of generators. Therefore, it is important to study the distribution characteristics and the influence factors of eddy current loss. Taking a 24-MW bulb tubular turbine generator as a reference, the influence factors that affect the eddy current loss of damper winding are analyzed.Design/methodology/approachA two-dimensional (2-D) electromagnetic field model of the generator is established, and the correctness of the model is verified by comparing simulation results and experiment data. The eddy current losses of damper winding in various conditions are calculated by using the finite element method.FindingsIt is identified that the cogging effect, pole shoe magnetic saturation degree, pole arc coefficient and armature reaction are the main factors that affect the eddy current loss of the generator rotor. When the generator is installed with magnetic slot wedges, the distribution characteristic of eddy current loss is obtained through the study of the eddy current density distributions in the damper bars. The variations of eddy current losses with time are gained when the generator has different permeability slot wedges, pole arc coefficients and pole shoe magnetic saturation degrees.Practical implicationsThe study of this paper provides a theoretical reference for the design and optimization of bulb tubular turbine generator structure.Originality/valueThe research can help enhance the understanding of eddy current distribution characteristics and influence factors of eddy current loss in bulb tubular turbine generator.

Analysis of Eddy Current Loss in Permanent Magnet Linear Synchronous Generator Considering Tapped Holes in Movers Using Semi-3-D Analytical Method

This paper describes the analysis of the eddy current loss of a double-sided cored slotless-type permanent magnet linear synchronous generator considering tapped holes in mover magnets using the space harmonic method. To calculate the eddy current, an analytical solution was derived by applying the Maxwell’s equation, magnetic vector potential, and Faraday’s law in a 2-D Cartesian coordinate system. Based on the armature reaction field distribution produced by the armature winding current, we obtained an analytical solution for the eddy current density distribution. Then, an analytical solution for eddy current loss induced in a permanent magnet (PM) was derived using the equivalent electrical resistance calculated from the PM’s volume and eddy current density distribution solution. Finally, the resulting current was determined based on the analysis of eddy current loss. The analytical results produced by using this application of the space harmonic method were validated extensively through comparisons with finite-element method results.

Eddy current density asymmetric distribution of damper bars in bulb tubular turbine generator

AbstractThe major reasons that cause the damage of damper bars in the leeward side are found in this paper. It provides a route for the structure optimization design of a hydro generator. Firstly, capacity of a 24 MW bulb tubular turbine generator is taken as an example in this paper. The transient electromagnetic field model is established, and the correctness of the model is verified by the comparison of experimental results and simulation data. Secondly, when the generator is operated at rated condition, the eddy current density distributions of damper bars are studied. And the asymmetric phenomenon of the eddy current density on damper bars is discovered. The change laws of the eddy currents in damper bars are determined through further analysis. Thirdly, through the study of eddy current distributions under different conditions, it is confirmed that the stator slots and armature reaction are the main factors to affect the asymmetric distribution of the eddy current in damper bars. Finally, the studies of the magnetic density distribution and theoretical analysis revealed the asymmetric distribution mechanism of eddy current density.

Electromagnetic properties of cylinder permanent magnet eddy current coupling

This paper focuses on the electromagnetic properties of new cylinder type twelve-pole permanent magnet eddy current coupling. By combining conventional equivalent magnetic charge method and superposition principle, the analytical calculation model of air gap magnetic field distribution for the cyli nder type permanent magnet eddy current coupling is established; by considering the skin effect, the analytical model of eddy current density is set; the analytical model of electromagnetic-transfer torque is given with the demagnetization effect taken into consideration. Based on the established analytical calculation model, the variation law of air-gap magnetic induction intensity, eddy current density distribution and magnetic torque characteristic curve are analyzed and plotted in detail. At the same time, finite element simulations of the air gap magnetic field, eddy current density and electromagnetic-transfer torque are carried out based on multi-physics, and the results are compared with analytical calculations. Moreover, the paper analyzed the thickness of magnet conductive plate impacts on eddy current and explored relations between torque and coupling distance under different pole pairs. Finally, in order to verify the simulations, the prototype test of torque transfer characteristics is carried out. This paper compares the experimental results with the theoretical analysis and simulation results, and finds out the error is within the allowable range.

Investigation of Gyroscopic Stabilization for Single-Stage Saddle Sextupole Field Electromagnetic Launcher

This paper presents a novel single-stage saddle multipole field electromagnetic launching mode for the realization of projectile linear acceleration with gyroscopic stabilization. The hollow cylindrical projectile with three symmetrical vertical slots can change the eddy current and magnetic field density distribution on the projectile surface. When twisted an angle relative to saddle multipole coils along the circumference, the projectile will be linear accelerated with spinning motion under the action of pulse current. In this paper, analytical calculations and simulation methods were used to analysis this mode, the simulation results indicated that the axial acceleration force and circumferential torque acting on the projectile were generated simultaneously, and an optimal initial twisted angle was existed to make the muzzle rotation speed reach peak. To verify the conceptual feasibility, a single-stage saddle sextupole field electromagnetic launcher was built and tested. The experiment demonstrate that the mode is indeed possible to realize the projectile linear acceleration moving with the gyroscopic stabilization, launching performance can be adjusted by changing the initial voltage or twisted angle, and the experimental results are accordant with the simulation results.

Effects of Laser Cladding Layers Width on Total Indicated Runout Characteristics of Steam Turbine Rotor Surface

In order to solve the wear repair problem of large steam turbine rotor shaft journal, the material of steam turbine rotor shaft was used as a substrate and the self-made special laser cladding remanufacturing powder as the experimental material, and the experiments were carried out by a laser cladding remanufacturing method based on the laser cladding remanufacturing system with coaxial powder feeder. Focusing on effect of different widths of laser cladding layers on total indicated runout (TIR) of steam turbine rotor, the experiment research and mechanism simulation verification were performed, and the influence mechanism of different factors were analyzed. The total data indicates runout are closely related to probe diameter and laser cladding layer width. The width of cladding layer determines the turbine rotor surface magnetic, eddy current density and magnetic flux density distribution. Due to the interference of matrix magnetic field and eddy current density of the surface, the magnetic flux density suddenly changes in the laser cladding layer edge when the laser cladding layer width is less than 8 mm. The measurement results are too large caused by the comprehensive effect of the substrate and the laser cladding layer. According to the numerical simulation of magnetic flux density distribution of measured metal body surface, the critical value of laser cladding width is 9.82 mm.

Proposal of slack inspection method of high tension bolt of hexagon head using alternating magnetic field

The development of the inspection technique of detecting the slack of the high tension bolt is desired. The permeability inside the side of the bolt head is changed since the bolt head is compressed by bolting a plate. Therefore, the evaluation of the slack of the bolt is possible by detecting the difference of the magnetic characteristics. In this paper, the inspection method for measuring the slack of the steel high-tension bolt of hexagon head using a small electromagnetic non-contacting sensor is proposed. The distribution of stress, flux density and eddy current density near the bolt head is estimated by 3-D nonlinear electromagnetic finite element method (FEM) analysis taking account of the electromagnetic property under various compressive stresses. The results showed that the non-destructive inspection of the slack of the high-tension bolts is possible by detecting the change of flux density in the side of the bolt head.