Leakage Magnetic Field Research Articles

The Influence of Flux Diverter Structures on the AC Loss of HTS Transformer Windings

Compared to conventional transformers, high temperature superconducting (HTS) transformers have higher efficiency and fewer hazards, whose main loss comes from the ac loss of high temperature superconducting windings carrying ac current. Their radial leakage magnetic fields are perpendicular of HTS winding tapes, which is the main parameter affecting the ac loss. In the study of superconducting magnets, the flux diverter has been used to reduce the radial leakage magnetic field. The effect of the flux diverter installed at the top of the transformer windings on the coil ac loss was explored in this paper. The influence of different structure, slotting, and the number of slots on the transformer was also discussed, which laid a theoretical foundation for the optimization of flux diverter on the 6.6 MVA HTS transformers. Besides, in this paper, we choose the homogenization treatment method to reduce the computing time and memory when modeling.

Design and Realization of an Open EPR Resonator at <inline-formula> <tex-math notation="LaTeX">${X}$ </tex-math> </inline-formula>-Band Frequencies

An open resonator compatible with $X$ -band commercial spectrometers for electron paramagnetic resonance was designed and built. In the design process, resonators with different shapes and dimensions were compared by using ad hoc defined cavity figures of merit. Three cylindrical cavities operating on TEX11 modes with $X = 1$ , 2, 3, were designed taking into account a coupling iris and a slit for microwave magnetic field leakage. The cavities were further improved toward the homogeneity of the 100 kHz modulation magnetic field. A cavity was then built, operating on TE111 mode; the measured electromagnetic parameters were in a good agreement with simulations. Finally, the cavity was inserted in a commercial $X$ -band spectrometer, and measurements have been performed on three paramagnetic samples: 2, 2-diphenyl-1-picrylhydrazyl, and irradiated alanine and bone.

A comparative study between magnetic field distortion and magnetic flux leakage techniques for surface defect shape reconstruction in steel plates

Both magnetic flux leakage (MFL) and magnetic field distortion (MFD) techniques are promising methods for surface defect detection in ferromagnetic components. The two techniques are based on different physical principles. However, their defect sizing and shape reconstruction abilities are seldom comparatively explored. In this study, finite element simulations and experiments were performed to achieve magnetic scanning imaging of a defective plate with both MFD and MFL techniques. First, the curves of voltage extracted from the lines crossing the center of cylindrical-hole defect (CHD) were used to evaluate the performance of several feature parameters in sizing the diameter and the depth of CHD. Second, the profiles of the normalized magnetic scanning imaging results were analyzed with a threshold plane to evaluate the abilities of MFD and MFL on reconstructing the shape of 8-shaped and cross-type through wall defects. Under the condition that the Hall device for measuring both the normal component of MFL and MFD has same lift-off distance as 1 mm, the MFD technique showed the advantages in defect shape reconstruction at the cost of available detection depth as compared with MFL techniques.

Numerical Study on the Leakage Magnetic Field of Transverse Defect on T-Joint Fillet Weld

Abstract A 3D finite element method model is established for yoke-magnetization detection of a transverse defect on T-joint fillet weld and solved by the finite element software ANSOFT Maxwell (ANSYS, Canonsburg, PA). The leakage magnetic field around the transverse defect is obtained. The relationship between the width of transverse defect and leakage magnetic field signals is identified. The researchers found that the tangential component of magnetic flux leakage density, BX1, tends to be a parabolic distribution and reaches the maximum value near the center of the defect along the length direction. While BX1 shows a bimodal distribution, featuring two peaks near the edge of the defect and one peak valley at the center along the width direction, the normal component of magnetic flux leakage density, BZ1, is very different than that of BX1 along the width direction, presenting an approximate N-shape as a whole. The leakage magnetic field signals of the transverse defect on the fillet weld of the T joint will decay obviously when the scanning line is perpendicular to the weld surface over 0.5 mm. The results of numerical simulation can provide a theoretical foundation to detect and characterize various defects in the fillet weld.

Discussion on the Principle and Reliability Improvement of AC Magnetic Flux Leakage Detection of Steel Rod

In this paper, the principle of ac magnetic flux leakage (referred to as MFL) detection is presented by analyzing the formation of ac magnetic flux leakage and how it is collected. It is found that ac excitation frequency is a very important equipment parameter for ac magnetic flux leakage detection of steel rod. High-frequency current not only stabilizes the penetration depth of ac magnetic field under the rod surface and leakage magnetic field of defects, but also improves the ability to detect defects and adapts to higher detection speed. It is concluded that the lift-off effect is the fundamental reason affecting the reliability of MFL detection of steel rod, and there is an inherent signal amplitude deviation from the irremovable probe bouncing on the surface of steel rod. Then, the factors that aggravate the lift-off effect are analyzed synthetically, and the corresponding countermeasures are put forward. It provides an effective basis for improving the test reliability and reasonably controls the quality risk of the rod.

Frequency Response of a Moving Two-Dimensional Defect in Magnetic Flux Leakage Inspection

The detection of magnetic flux leakage (MFL) enables nondestructive detection and characterization of defects in magnetic structures. In this letter, Fourier transforms of the leakage fields from a two-dimensional surface defect are evaluated to produce analytical expressions for the frequency response of MFL signals detected by a flux-sensitive sensor. The expressions show the correlation between the spectral response of the leakage fields, defect dimensions, and sensing element lift-off spacing as a product of frequency-dependent defect-width loss function, spacing loss function, and thickness enhancement function. The lower and upper band edges of the band-limited leakage magnetic fields are theoretically identified. A spectral method for sizing of defects is proposed based on the frequency response.

Influence of Magnetic Permeability of the Press Plate on the Loss and Temperature of the End Part in the End Region of a Turbogenerator

Press plates are widely used in the end region of turbogenerators. However, due to the effect of magnetic field leakage from the end region, the eddy current losses of the copper screen and press plate will result in the copper screen and press plate having a high temperature under the rated load condition. In this paper, the influence of the magnetic permeability of the press plate on losses and temperature of the end region is researched in turbogenerators. Three-dimensional (3-D) fluid and thermal mathematic and physical models of the turbogenerator end region are established. Under different magnetic permeability values of the press plate, a 3-D transient electromagnetic field in the turbogenerator end region is calculated, and the obtained losses of the end parts are treated as heat sources. Fluid network equations are calculated, and the obtained fluid velocity and pressure values are applied to the end region as boundary conditions. After solving the fluid and thermal equations, fluid velocity around the surface of the end parts is obtained under the rated load condition. The temperature distribution of the end parts is determined for different magnetic permeability values of the press plate. The calculated temperature results agree well with the test data.

New Experimental Limits on Exotic Spin-Spin-Velocity-Dependent Interactions by Using SmCo_{5} Spin Sources.

Despite the great success of the standard model (SM), there still exist mysteries like the nature of dark matter, the strong CP problems, etc. To solve them, many theories proposed new bosons beyond the SM that can mediate new forces. Here, we report the latest results of searching for possible new long-range spin-spin-velocity-dependent forces (SSVDFs), based on specially designed iron-shielded SmCo_{5} spin sources and a spin exchange relaxation free comagnetometer. With help from the similarity analysis method, new constraints on some forms of SSVDFs between electrons have been obtained, which represent up to more than 11 orders of magnitude tighter limits than previous experiments for the force range of 5cm-1km.

Relationship Between Drive Frequency and Load Characteristics in Bidirectional Contactless Power Transfer for Electric Vehicles

Vehicle to home (V2H) attracts attention as a way to use electric cars. In V2H, it is necessary to exchange electricity between the electric car and the household. Therefore, bidirectional contactless power feeding technology is effective. In bidirectional non-contact power feeding, it is required that the performance does not deteriorate even if the power transmitting side and the power receiving side are switched. Therefore, it is effective that the capacitor is symmetric as a capacitor connecting method for efficiency compensation and power factor improvement. We adopt the series–series (SS) system connecting the capacitors in series to the coil. However, in the case of the SS method, if the load fluctuates, the current on the primary side increases and the leakage magnetic field increases. Also, an increase in the primary current causes an increase in the output voltage. Therefore, in this paper, in order to suppress the primary current at light load and to stabilize the output voltage, a method of controlling the drive frequency was proposed. As a result, by selecting an appropriate drive frequency, it was possible to suppress increase in the primary side current at light load and realize voltage stabilization.

Accurate Position Detection in Wireless Power Transfer Using Magnetoresistive Sensors for Implant Applications

Recently, the utilization of magnetic resonant coupling (MRC) mechanism for wireless power transfer (WPT) has been actively investigated. Among numerous applications of WPT technology, the energization of implanted biomedical devices wirelessly and uninterruptedly from external supply is important because it can eliminate possible device replacement due to battery depletion. Given the implanted receiver is invisible from the external transmitter, the coil misalignment occurs easily which results in low transfer efficiency and high magnetic field leakage, and consequently endangers the human health [1]. Thus, the development of accurate position detection of the implanted receiver from the external transmitter is highly desirable. Presently, most studies of the position detection in WPT are focused on the application of electric vehicles. Although the corresponding technologies such as coil sets [2] or auxiliary multi-coils [3] have achieved fruitful outcome, they are too bulky and complicated to be used in implant applications. Due to the advantages of high stability, small size, low power consumption and high precision, the magnetoresistive (MR) sensor has been widely used in many industrial applications [4]. Generally, they are arranged in an array style to measure the magnetic field vector [5] or a moving magnetic object [6]. To the best of authors' knowledge, the application of MR sensors in WPT is absent in literature. In this paper, a new position detection approach in WPT is proposed and implemented, which is particularly suitable for implant applications. The key is to use a MR sensor array to directly measure the variation of magnetic field so as to precisely detect the relative position of the implanted receiver from the external transmitter. Therefore, the advantages of efficient and compact WPT for implant applications can be achieved.

A Fluid-Solid-Magnetic Coupling Algorithm of Internal Crack Growth in the Weld of Oil and Gas Pipelines

In order to characterize the dynamic process of the crack growth in the weld of oil and gas pipelines, a mathematical model of fluid-solid-magnetic multifield coupling was constructed in this paper. Based on this model, the bidirectional fluid-solid coupling and unidirectional magnetic structure coupling caused by the weld deformation were achieved by dynamic application of the fluid permeation pressure, calculating the internal crack growth in the pipe weld, reconstructing the computational grid near the internal crack, and discussing the characteristics of the magnetic leakage field in the process of the internal crack growth in pipe weld. Thus, a fluid-solid-magnetic coupling algorithm for the internal crack growth in pipe welds considering fluid permeation pressure is established. According to the characteristics of the internal crack opening distance, internal crack growth length, crack tip energy release rate, peak values of magnetic induction intensity level, and vertical component, the process of the internal crack growth is measured. The results show that the fluid osmotic pressure accelerates the process of the internal crack growth and this algorithm can solve the problem of the characterization and evaluation of crack growth in pipe welds under fluid-solid-magnetic coupling action.

A hybrid shielding structure for reduction of the leakage magnetic field in wireless power transfer system

AbstractIn this paper, we propose a hybrid shielding structure for the reduction of the leakage magnetic field in the wireless power transfer (WPT) system operating at 175 kHz. This structure consists of ferrite slab staked on the aluminum plate. The improvement in the magnetic field reduction is achieved, while minimizing the power transfer loss by optimizing the design parameters. The power transfer efficiency and leakage magnetic field are analyzed and verified through simulation and experiment. The experimental results show 77% power transfer efficiency with proposed structure, while the normalized leakage magnetic field strength was reduced up to 80% compared with the conventional shielding structures.

Simulation and Analysis of Leakage Magnetic Field of PMSM Based on Comsol Multiphysics

When using rotary aircraft equipped with three-axis magnetometer for measurement, the magnetometer is often affected by the leakage magnetic field from the permanent magnet synchronous motor (PMSM) on the aircraft. The analysis of the characteristics of the leakage magnetic field of PMSM is helpful for the determination of the installation position of the magnetometer and cancellation of the interference of the leakage magnetic field when measuring the external environment magnetic field. In this paper, a three-dimensional PMSM model has been simulated by using Comsol Multiphysics software, and the leakage magnetic field of the motor was investigated. According to the simulation results, we find that the phase of the leakage magnetic field varies linearly around the center of the motor in space, and the amplitude decays exponentially in different directions.

Research of leakage magnetic field in deenergized transformer

PurposeThe paper presents the analysis of magnetic field that surrounds the power transformer after it has been switched off. The purpose of this paper is to determine the possibility of defining the residual fluxes in the legs of the transformer based on the measurement of this field. It was also intended to determine the type and the location of magnetic sensors.Design/methodology/approachNumerical analysis of the magnetic field was performed. A three-dimensional model of the transformer’s magnetic core was created in the Flux 3D simulation program. The analysis was concerned with an oil-filled transformer and a dry transformer. The magnetic field of Earth was taken into account.FindingsThe research has shown that magnetic induction of the leakage field produced by residual magnetization of the core is comparable to the magnetic induction of the Earth’s field. It was also found that the measurement of the magnetic induction should be performed as close as possible to the core. The interior of the tank turned out to be a convenient space for the placement of the sensors.Research limitations/implicationsThe influence of external ferromagnetic objects, and devices generating magnetic field, on the measurement was not considered. It should be taken into account in the future work.Originality/valueOn the basis of the analysis, it was proposed to measure the magnetic induction vector of the leakage field at three points. The sensors should be placed in front of the columns at a position that is half of their height. The measurement can be performed with satisfactory accuracy by sensors located on the surface of the windings.

Analysis on Spatial Spectrum of Magnetic Flux Leakage Using Fourier Transform

As an efficient non-destructive testing method, magnetic flux leakage (MFL) has been widely used for damage detection in ferromagnetic materials. The magnetic dipole theory is a traditional method to calculate the magnetic leakage field. In this paper, the magnetic leakage field functions of a slot in a 2-D infinity plate are obtained using the magnetic dipole theory. Equations of the magnetic leakage field are converted into the convolution of two other functions. Spatial spectral equations of the MFL are developed according to the convolution theorem using the Fourier transform (FT) method. The results are analytical functions different from other numerical methods, such as the discrete FT and fast FT methods, and the calculation speed is fast. The results show that the $y$ -component of the magnetic leakage field has 90° phase shift with the $x$ -component. This result has clear physical significance compared with the traditional MFL equations using the magnetic dipole theory. Different spatial spectral curves for different defects are presented in this paper. Since there is a sinc function for the width value in the equation, the width value can be deduced from the first zero-crossing point in the spatial spectrum curves. A new method is proposed to determine the width value using the relationship $w =1/f_{s}$ , where $f_{s}$ is the first zero cross point. Two specimens with different cracks are investigated, and the experimental results show this method can be used as an inverse MFL data interpretation technique.

Comparison of Tripolar and Circular Pads for IPT Charging Systems

Recently, a magnetic pad called the tripolar pad (TPP) has been introduced for inductive power transfer (IPT) systems. This paper evaluates the effective coupling factor and leakage magnetic field of a 20-kW IPT system that uses a combination of TPP and circular pad (CP) topologies over a range of lateral displacements. The results show that the effective coupling factor and the leakage magnetic field of the TPP–TPP system are substantially better when the secondary is displaced away from ideal alignment. Leakage magnetic field is reduced up to 43% compared to the CP–CP system at the worst-case misalignment, which is due to the ability of the TPP–TPP system to generate and capture different types of magnetic field shapes. Simulation methods for both the TPP and CP are validated in the laboratory using a 2-kW system operating at 85 kHz.

Modeling and Experimental Studies on 3D-Magnetic Flux Leakage Testing for Enhanced Flaw Detection in Carbon Steel Plates

ABSTRACTFor enhanced detection of flaws in engineering components using magnetic flux leakage (MFL) technique, measurement of the leakage magnetic field components along the three perpendicular directions is beneficial. This article presents the three dimensional-magnetic flux leakage (3D-MFL) modeling and experimental studies carried out on carbon steel plates. Magnetic dipole model has been used for the prediction of MFL signals and images. Sensitivity of the MFL signals peak amplitudes of tangential (HX), circumferential (HY), and normal (HZ) components with respect to flaw length, width, depth and lift-off have been studied. A 3D-GMR sensor has been used for simultaneous measurement of all the three components of leakage magnetic fields from surface flaws in 12 mm thick carbon steel plates. The experimental MFL images have been compared with the model predicted MFL images. The sensor has shown the capability to detect and image 0.9 mm deep surface flaws with a signal to noise ratio of 8 dB. Principal component analysis (PCA)-based image fusion has been performed for fusion of the 3D-MFL images to obtain a geometrical profile of the flaws. Study reveals that 3D-GMR enhances the capability for detection of flaws having irregular geometries.

End-Effect Magnetic Field Analysis of the Halbach Array Permanent Magnet Spherical Motor

The Halbach array permanent magnet (PM) spherical motor (PMSM) consists of a spherical rotor and a spherical-shell stator. The magnetic field distribution surrounding the rotor PMs is closely related to the spherical structure of the Halbach array PMSM. The Halbach array PM configuration characteristics lead to the end leakage magnetic field in the latitudinal direction of the spherical structure, which is end effect. Establishment of an accurate 3-D magnetic field analytical model containing the end leakage magnetic field of the Halbach array PMSM is the foundation of magnetic field distortion research with its influence on eddy-current loss. The magnetic field distribution of the Halbach array PMs in the air gap is calculated using the scalar magnetic potential. Laplace and Poisson equations of the scalar magnetic potential in the spherical coordinate system are derived. To analyze the end leakage magnetic field of the Halbach array PMSM in the latitudinal direction, concept of mechanical pseudo-cycle in the motor latitudinal direction is proposed, and the cycle of Fourier series is redefined. A completed 3-D analytical expression of the Halbach array PMSM magnetic field distribution is derived by the new Fourier series and spatial integral technology, in which the end leakage magnetic field is contained. The results obtained by the proposed analytical method are compared with the numerical results, i.e., the results obtained by the finite-element method, which verify the effectiveness of the analytical method. Magnetic field distribution containing the end leakage magnetic field in different magnetization methods is compared and analyzed, which shows that the Halbach array magnetization has a larger main air-gap magnetic field and a smaller end leakage magnetic field. The effect of motor structure parameters on the end leakage magnetic field is analyzed, and the effect of end leakage magnetic field on eddy-current loss is preliminarily discussed, which shows that eddy-current loss caused by end effect almost accounts for half of the total eddy-current loss. The research on end effect and the effect of motor parameters on end effect are of great significance. In the end, the leakage magnetic field results obtained by the proposed analytical method are verified by the experimental results.

Excitation Effect Analysis of a Novel HTS Controllable Reactor With Orthogonally Configured Core Based on Dynamic Inductance Matrix

The controllable reactor is one of the most effective methods for compensating reactive power. A novel type of high temperature superconducting (HTS) controllable reactor with orthogonally configured core has been proposed, analyzed, and developed. However, for the controllable reactor with dynamic inductance, the excitation analysis based on field circuit coupled method is inefficient and the excitation parameters optimization is more difficult. In this paper, an excitation system containing a voltage source converter and buck–boost converter is established. The reactor is built as a self-defined nonlinear element in the system model based on the dynamic inductance. The inductance matrix, core saturation, leakage magnetic field at HTS winding, and total magnetic flux in the excitation core are included in the self-defined element. The parameters of the excitation system have been optimized easily. The simulation result of the output characteristic of the reactor is consistent with the experimental observations of the prototype. The dynamic inductance method is proved to be fast and effective.

Investigation of End Leakage Reactance and Its Influence on the Accuracy in Performance Calculation of Large Double Canned Induction Motors

The end leakage reactance of large double canned induction motors is important for the performance calculation by two-dimensional (2-D) numerical analysis, which calculation accuracy directly affects the calculation results of performances. However, there are many special metallic structures in the end region of large double canned induction motors. Due to these structures, the distribution complicacy of end magnetic fields and the calculation difficulty of the end leakage reactance are increased. To solve this problem, a 5-MW double canned induction motor is taken as the research object; 3-D finite element calculation model of its end region is established and solved. The end magnetic field and end leakage reactance are obtained. The influence of these special structures on the end magnetic field and end leakage reactance are analyzed in detail. Performances of large double canned induction motors are calculated by the 2-D numerical analysis with different end leakage reactance coupling. The calculation results of the end leakage reactance are indirectly verified through the stator current and power factor as the accuracy of the end leakage reactance directly affects calculation results of the stator current and power factor.