Showing papers on "Magnetic core published in 2023"

Diamond-Window Resonant Inductor with Significant AC Flux

Abstract: Resonant inductor with significant ac flux at MHz switching frequency is challenging because of high core loss and winding loss due to skin and proximity effect. Air gap brings in fringing magnetic field resulting in uneven current distribution and therefore higher winding loss. The conventional rectangular-window core is replaced by the diamond-window core to reduce the fringing flux on the winding and therefore results in smaller inductor loss. An inductor prototype was built and was placed into a 200W Series-Resonator Buck (SRB) converter at 48V input voltage and 40A output. Experimental results are discussed to verify the theoretical analysis.

Mathematical Modeling and Validation of Saturating and Clampable Cascaded Magnetics for Magnetic Energy Harvesting

Abstract: Electromagnetic energy harvesting extracts energy from magnetic fields and can provide power to sensors, monitoring nodes, cyber-physical systems and control elements without additional battery and external power source and wiring. This article presents a novel ac-driven electromagnetic energy harvester based on periodically saturating, cascaded magnetics, consisting of a clampable magnetic core and an ungapped high permeability core. The high permeability core guarantees the maximum energy extraction, whereas the clampable core enables the nonintrusive installation of the energy harvester for more pervasive applications. This article first builds a comprehensive mathematical model based on this saturating cascaded magnetic structure, considering the reachability of an individual saturation flux density of the two magnetic cores. This model resolves the new challenges introduced by the cascaded magnetics with respect to a traditional single-core case, providing the accurate calculation of the lengths of the relevant time windows for harvesting and the amount of the harvested power. Our mathematical model is verified against simulation and experiment, showing excellent agreement among them with the maximum discrepancy of less than 6%. This article also reveals that the maximum power extraction occurs when the ungapped core operates in its slightly saturated state and that the harvested power increases with a higher primary current as well as a higher line frequency.

Optimization of Core Size and Harvested Power for Magnetic Energy Harvesters based on Cascaded Magnetics

Abstract: Magnetic energy harvesting (MEH) extracts energy from magnetic fields generated from AC current, providing power for environmental sensors, Internet of Things (IoTs), and monitoring nodes. The cascaded-magnetic-based electromagnetic energy harvesters, consisting of a clampable core and a high-permeability ungapped core, feature relatively higher density and predictability in energy harvesting. The clampable core only facilitates a non-intrusive mounting of the energy harvester onto the primary wire while the high-permeability core is the heart of the energy harvester to guarantee the maximum power extraction and usable output voltage. Therefore, reducing the clampable core size is critical to increase the power density without drastic power degradation. This article first presents the optimization conditions of the clampable core volume based on the harvested power level and other design requirements. FEM simulations using Ansys Maxwell and LTspice simulations are both executed to show the influence of the core parameters on the amount of harvested power and core saturation. This paper also presents an energy improvement method, controlling power transfer window via active switches, to improve the harvested power level. The boosted power is evaluated in this paper via experimental results.

A Passive Negative Magnetic Reluctance Structure-Based kHz Transformer for Improved DC Magnetic Bias Withstanding

Abstract: How to effectively withstand the dc magnetic bias is one of the key aspects of transformer design. General approaches either require additional active power electronics devices or apply complicated control strategies, causing the increased cost or reduced reliability. In this article, a passive negative magnetic reluctance structure (NMRS) is proposed and installed in the air gap of the open-core transformer, which could achieve improved dc magnetic bias withstanding capability without extra active devices. The key criterion of the proposed design is to employ the NMRS with a frequency-variation magnetic reluctance property as a magnetic bandpass filter, which shows a negative equivalent magnetic reluctance for the fundamental component of flux. Nevertheless, it presents a high magnetic reluctance for the dc component. With the proposed design, the transformer provides a strong withstanding dc bias capability and a low magnetizing current as well as high efficiency. Accordingly, both the advantages of open-core and closed-core transformers could be obtained with the proposed design. For verification, a 500-W EE55-based core prototype is constructed and verified with sinusoidal and square wave excitation. Electromagnetic analysis and experimental results are provided to demonstrate the effectiveness of the proposed design.

Influence of tensile stress on the magnetic properties of ultra-thin grain-oriented electrical steel

Abstract: Ultra-thin grain-oriented electrical steel (GOES) with thickness less than 0.1 mm can be used to make the iron core of the reactor and high-power magnetic amplifiers. The design of these electromagnetic devices often relies on the data of magnetic characteristics measured under standard sinusoidal excitation. However, the influence of working conditions such as stress and temperature are ignored. The magnetic properties of the magnetic materials under stress are quite different from those under sinusoidal excitation. It is very important to accurately measure the magnetic properties of ultra-thin GOES under stress conditions. This article presents and analyzes the extensive experimental results of magnetic properties in the rolling direction with uniaxial and biaxial tensile stress applied by piezoelectric materials.

Design of an Air-Core Circuit for a Magnetically Shielded Hall Thruster

Abstract: The magnetic field of the SPT-100 is reproduced computationally using an air-core magnetic circuit. The air-core circuit is comprised of a group of solenoids distributed throughout the thruster body. An optimization problem is defined to translate and rotate the solenoids so that the L2 norm between the measured magnetic field of the SPT-100, and the predicted magnetic field of the solenoids is minimized. The problem is constrained such that the solenoids do not intersect each other or the thruster boundary. It is found that the air-core solution can replicate the design magnetic field with L2 norm of 11.2 G. The power produced by this circuit was calculated to be 369 W. It was also found that an air-core circuit may reduce the mass of the thruster by >50% compared to traditional ferromagnetic circuits.

Performance Comparison of Tubular Flux-Switching Permanent Magnet Machines Using Soft Magnetic Composite Material and Hybrid Material Magnetic Cores

Abstract: The magnetic core of a conventional tubular flux-switching permanent magnet machine (TFSPMM) is made of axially laminated silicon steel sheets. The laminated direction is consistent with the motion direction of the mover. According to the flux-switching principle, a large amount of eddy current loss will be generated when the alternating flux passes through the silicon steel sheets vertically. The soft magnetic composite (SMC) material is magneto-thermal isotropy and has low eddy current loss, which can be used in TFSPMM. However, the permeability of SMC is much lower than that of silicon steel sheets, and the hysteresis loss is large at low frequency. When the two materials are used as the hybrid material magnetic core in the machine, their respective advantages can be used to improve the thrust force of the machine and reduce core loss. In order to study the effect of SMC core and hybrid material magnetic core on the machine, the performances of TFSPMM with different kinds of cores are calculated and compared by finite element method (FEM), including magnetic density distribution, permanent magnet (PM) flux linkage, back-electromotive force (EMF), inductance, detent force, thrust force and core loss. Finally, a prototype machine with hybrid material magnetic core is made and experimental verification is carried out.

AC Loss Reduction in HTS Coil Windings Coupled With an Iron Core

Abstract: Rapid-cycling synchrotron (RCS) magnets based on a superferric design consist of high temperature superconducting (HTS) coil windings coupled with iron cores. However, the presence of iron cores significantly increases AC loss in HTS coil windings, making AC loss reduction a critical issue for applying HTS technology in RCSs. Enlarging the distance between iron cores and coil windings may reduce AC loss. In addition, magnetic materials with different saturation magnetic fields also may influence AC loss in HTS coil windings coupled with iron cores. To investigate the distance dependence, AC losses of 1DPC (double pancake coil)-, 2DPC-, 4DPC-, and 8DPC assemblies with various distances are simulated using the 3D T - A homogenization method with/without an iron core. Two magnetic materials with different saturation magnetic fields are chosen as the iron core to evaluate AC loss in HTS coil assemblies. The results show that the AC loss values in HTS coil assemblies coupled with the iron core decrease significantly with growing distance. For a given distance and current, when the iron core has a lower saturation field, the AC loss values of the 4DPC assembly are smaller than those with a higher saturation field.

Methodology for Eddy Current Losses Calculation in Linear Variable Differential Transformers (LVDTs)

Abstract: Linear variable differential transformer (LVDT) is a commonly used linear displacement sensor because of its good measurement characteristics. When using laminated ferromagnetic cores in LVDTs, it is very important to take eddy currents into the account during design phase of the sensor. Particularity of the open-type core means that the eddy currents induced by the stray magnetic flux that flow in large loops tangential to the lamination surfaces take on significant values. Due to the open-type core a typical LVDT has, depending on the core material, it is, therefore, very important to take eddy currents into the account when designing the sensor. This paper’s goal is to present a methodology for calculating LVDT eddy current losses that can be applied to LVDT design in order to optimize the dimensions and help with selection of materials of the LVDTs, in order to achieve the highest measurement accuracy. Presented approach using an AτA-formulation with elimination of redundant degrees of freedom exhibits rapid convergence. In order to calculate the relationship between eddy current losses and core displacement, frequency, and material characteristics, a number of 3D finite element method (FEM) simulations was performed. Analysis of the obtained results using presented methodology for eddy current losses calculation in LVDTs enables the designer optimize the design of the LVDT.

Study of Nonlinear Excitation Circuits for Fluxgate Magnetometer

Abstract: This paper presents the common methods and corresponding drawbacks concerning nonlinear analysis of fluxgate excitation circuits and emphasizes the importance of nonlinear analysis for these circuits. With regard to the nonlinearity of the excitation circuit, this paper proposes the use of the core-measured hysteresis curve for mathematical analysis and the use of a nonlinear model that considers the coupling effect of the core and winding and influence of the historical magnetic field on the core for simulation analysis. The feasibility of mathematical calculations and simulation for the nonlinear study of fluxgate excitation circuit is verified via experiments. The results demonstrate that, in this regard, the simulation is four times better than a mathematical calculation. The simulation and experimental results of the excitation current and voltage waveforms under different excitation circuit parameters and structures are essentially consistent, with a difference in current of no more than 1 mA, thereby verifying the effectiveness of the nonlinear excitation analysis method.

At What Frequencies Should Air-Core Magnetics Be Used?

Abstract: Magnetic components for power conversion (inductors and transformers) are often designed with magnetic cores, which add core loss but reduce the required number of turns, copper loss, and usually total loss. At very high frequencies, poor core materials make this tradeoff less advantageous and air-core magnetic components are often preferred. The boundary between the magnetic-core-preferred and air-core-preferred regimes has not yet been theoretically identified, and intermediate frequency ranges (e.g., 5–30 MHz) see both cored and air-core examples. In this work, we calculate various expressions that suggest that cored inductors can outperform their air-core counterparts up to many tens of megahertz on a volumetric basis and about 10 MHz on a mass basis, based on the properties of currently available magnetic materials. We experimentally demonstrate the boundary frequencies by comparing the quality factors of optimized magnetic-core and air-core toroidal inductors. Formally demonstrating the advantage of magnetic-core over air-core inductors suggests more advantageous design strategies at tens of megahertz, with significant impact on applications at industrial, scientific, and medical frequency bands (6.78, 13.56, and 27.12 MHz) and other radio frequencies.

Analysis of magnetic field characteristics and no-load losses of three-dimensional wound core transformer

Abstract: Three-dimensionally wound core transformers (TWCTs) are widely used because of their low iron loss. This paper investigates the triangularly arranged TWCT core structure and a conventional planar laminated core transformer’s flat “E” core structure (PLCT). First, the magnetic field structures of the two transformers are analyzed using the equivalent magnetic circuit method to study the symmetry of the three-phase reluctance. Then, using the finite element method, a three-dimensional simulation model was built to analyze the no-load performance of TWCT and PLCT with the same dimensional parameters and the same core material. The no-load flux of each coil, the induced voltage on the secondary side, and the no-load iron loss of the core are analyzed. The analysis results show that TWCT has a 7.48% lower no-load loss than PLCT, which verifies the superiority of TWCT in terms of no-load loss.

Development of Rotor Core with High Magnetic Flux by Partial Non-Magnetic Improvement of Silicon Steel

Abstract: Flux leakage in the rotor core bridges is a problem specific to interior permanent magnet motors and has been unsolved till date. It is widely known that if the bridges are partially non-magnetically improved with low magnetic polarization, the leakage flux will be smaller, and the rotor will have a higher magnetic flux. We proposed that the portion of the silicon steel sheets that becomes the bridge after pressing can be non-magnetized and laminated to fabricate the rotor core. Partially non-magnetic material with a polarization of almost zero was obtained by melting and mixing Ni–Cr alloy powder with the silicon steel sheets. This non-magnetic improvement treatment was applied to the bridge in the rotor core sheet, in which the non-magnetic area width was 1.45 mm, and the prototype rotor core was fabricated by laminating 60 rotor core sheets. Upon measurement, the rotor core showed approximately 35% higher magnetic flux than a conventional one, with the actual value nearly identical to that obtained from the magnetic field analysis.

Design of an Iron Loss Tester for the Evaluation of Assembled Stator Cores of Electric Machines

Abstract: The manufacturing processes of an electric machine can lead to a deviation between predicted and actual iron losses. This work presents an iron loss tester for measuring the iron losses produced by an assembled stator core including the effects of manufacturing and actual flux distribution. The tester is designed with accessible excitation and measurement windings with a toroidal configuration enabling a high degree of flexibility in emulating various flux distributions in AC electric machines. A prototype of the proposed tester is built and the experimental results of a manufactured stator are obtained under different pole configurations showing the magnetization characteristics in different regions of the tester/stator along with the total measured iron loss (IL). A noticeable deviation between experimental and FE simulation results is present at high frequencies. As the saturation level in steel laminations is reduced, the deviation in total IL is increased. Finally, the specific IL obtained through the tester is compared against standard Epstein frame results. Importing the experimental IL data obtained through the tester to the FE model led to a close match between simulation and experimental results.

Numerical Model for Eddy-current Loss of Wound Core in Single-Phase Transformer

Abstract: Taking the wound core transformer widely used in the field of traction energy saving as the research object, considering its unique geometric structure, combined with the magnetic circuit theory and finite element calculation of Ansys Maxwell software, the phenomenon of the magnetic flux distortion of the wound core is revealed, and the influence degree of various factors is analyzed; based on the Maxwell equation system of the magnetic quasi-static field, the calculation model of the magnetic flux distortion considering joints is deduced, and then the numerical calculation model of the eddy-current loss of the wound core considering the magnetic flux distortion is presented, which is verified by no-load tests and can reflect the change of the eddy-current loss caused by the geometry of the core with different frequencies and magnetic flux densities, and it can be applied to large-capacity traction transformer with calculation error less than 3%. The numerical model can quickly calculate the eddy-current loss by core structure parameters and material properties without sample preparation and simulation in design stage, which greatly saves engineering cost and can be used for structural design and optimization of the wound core.

Investigation of the Temperature Field Distribution in an EI Type Iron-Cored Coil Using 3D FEM Modeling at Different Load Conditions

Abstract: In this present paper, results for the temperature distribution in electromagnetic construction in the form of coil coupled with EI-type ferromagnetic core are presented. This construction is typical for small electric transformers (AC operation mode) or chokes—DC or AC operation mode. Investigation has been provided using 3D finite element method computer modeling at various load conditions to simulate power dissipation both in the coil and the core volumes. The results obtained were used to calculate overall thermal resistances toward ambient free air and the thermal resistance between the coil and the core. These results show the important role the thermal resistance between the coil and the core may play for both steady-state and transient device operation.

A Compact Saturated Core Fault Current Limiter Magnetically Integrated with Decoupling Windings

Abstract: Traditional saturated core fault current limiters (SCFCLs) have fast rising fault state inductance that can limit faults automatically. However, the current limiting performance of traditional SCFCLs is insufficient. In order to improve this, some novel SCFCLs use additional air core reactors, resulting in a large volume and floor area. A compact saturated core fault current limiter magnetically integrated decoupling windings (CSFCL) is proposed in this study, which has the advantages of a smaller volume and floor area. The principle of the non-orthogonal decoupling method is firstly introduced. The core body of the CSFCL is then magnetically integrated with the decoupling windings in the form of non-orthogonal decoupling. Equivalent magnetic circuit and electric circuit analysis is carried out. An inductance calculation method for decoupling windings is proposed. Following this, a 220 kV simulation model is conducted based on the finite element method. Finally, a small-capacity prototype of the CSFCL and a test platform are designed to test it. The experimental results verify the correctness and feasibility of the proposed structure.

Optimized Weight Low-Frequency Search Coil Magnetometer for Ground–Airborne Frequency Domain Electromagnetic Method

Abstract: The vertical component magnetic field signal in the ground–airborne frequency domain electromagnetic (GAFDEM) method is detected by the air coil sensor, which is parallel to the ground. Unfortunately, the air coil sensor has low sensitivity in the low-frequency band, making it challenging to detect effective low-frequency signals and causing low accuracy and large error for interpreted deep apparent resistivity in actual detection. This work develops an optimized weight magnetic core coil sensor for GAFDEM. The cupped flux concentrator is used in the sensor to reduce the weight of the sensor while maintaining the magnetic gathering capacity of the core coil. The winding of the core coil is optimized to resemble the shape of a rugby ball, taking full advantage of the magnetic gathering capacity at the core center. Laboratory and field experiment results show that the developed optimized weight magnetic core coil sensor for the GAFDEM method is highly sensitive in the low-frequency band. Therefore, the detection results at depth are more accurate compared with those obtained using existing air coil sensors.

Optimal Air Gap Length Design in Powder Core Inductors

Abstract: The main requirements of magnetic components for power electronics applications are high power density and low power losses, driven by the need for more compact and more efficient power converters. Metal powder materials are a common choice for high-power and high-frequency inductors subject to a large magnetic field bias, since they feature high saturation flux density and low magnetic permeability (i.e., a “distributed” air gap), allowing for the adoption of un-gapped cores. Despite this, under high values of magnetomotive force (i.e., deep core magnetic saturation), the insertion of a concentrated air gap can lead to higher core inductance factor values with respect to an un-gapped configuration. In this context, this paper proposes a straightforward procedure to maximize the inductance factor of metal powder magnetic cores by identifying the optimal air gap length for a specified design operating point. In particular, the procedure completely relies on information available in the core manufacturer’s datasheet and does not require experimental characterization of the core itself, dramatically simplifying the inductor design procedure. The proposed methodology is theoretically described and then experimentally validated on an XFlux®60 core from Magnetics.

Measurement and Analysis on Magnetic Field Influence of Substation for Magnetic Shielding Device

Abstract: The residual magnetic field in a magnetic shielding device with a multilayer high permeability material (permalloy) structure can be obtained at the nanotesla (nT) level or even lower. At present, in the process of designing a magnetic shielding device, most of the external environmental magnetic field settings are set at the size of the Earth’s environmental magnetic field, but the instruments inside the magnetic shielding device need to be powered, the active compensation coil needs to be powered, and the degaussing coil of passive shielding layer needs to be powered, so substations need to be used around magnetic shielding devices. The magnetic field generated by the substation will affect the magnetic shielding device, so this paper analyzes and measures the magnetic field generated by the substation. Firstly, the finite element model of a substation is established, and the influence of different substations on the environmental magnetic field is analyzed by changing the power. Secondly, the test method of a substation environment magnetic field is determined. Finally, the site test was carried out to measure the influence of different power substations and different distances on the magnetic field, and its influence on the magnetic shielding device was analyzed, which provided an important basis for the construction of the magnetic shielding device.

Stator Core Design of 10 Mvar Superconducting Synchronous Condenser

Abstract: The air gap flux density of the superconducting synchronous condenser is high. If the stator core uses a magnetic teeth structure, the teeth are easily overheating. For a 10Mvar superconducting synchronous condenser, Firstly, based on electromagnetic design and ventilation cooling calculation, the stator windings are determined to be water-cooled, and the radial ventilation channels are 10 grades. Then the stator core structure design without magnetic teeth is proposed, and the core slot and core end, and fastening structure are obtained. Two sets of clamping rings are used to realize the radial tightening of the core. Finally, a single tooth and single slot finite element model of the non-magnetic tooth was established, and the structural strength of the non-magnetic teeth was analyzed. The results show that the non-magnetic teeth meet the strength requirements of the rated condition and the strong excitation condition.

Mathematical Model and Simulation Based on ANSYS Maxwell of the Magnetic Fluid Differential Transformer Inclination Sensor

Abstract: A mathematical model of a mutual inductance magnetic fluid inclination sensor is established. The sensing element of the sensor is magnetic fluid. The composite magnetic core suspended in the magnetic fluid increases the permeability of the medium in the winding. The total magnetic induction intensity B in the winding is composed of two parts: the excitation magnetic induction intensity Bl and the additional magnetic induction intensity Ba generated by the magnetization of pure iron. The sensitivity S of the sensor and its influencing factors are derived. The output characteristics of the sensor are analyzed using ANSYS Maxwell simulation software. The results show that the variable resistance of the measuring circuit can eliminate the residual voltage at zero point, and the output voltage carrier after filtering and rectification is positive half cycle; The addition of pure iron to the magnetic core greatly increases the mutual inductance variation between the primary and secondary windings, and the inclination angle in a small range is linear with the mutual inductance variation; The recovery force of the composite core is proportional to the displacement.

Simulation of Stray and Core Shielding Loss for Power Transformer Based on 2D/3D FEM

Abstract: In recent years, the capacity has increased and the volume has been limited in the power transformers. The stray losses of the tanks and structural parts cannot be ignored in the load loss. The tanks and the structural parts are complex structures. It is difficult for transformer manufacturers to use analytical methods to calculate stray losses for each component in the power transformers. If the stray loss distribution of the components can be estimated, it will help to optimize the power transformer’s cost and performance. Therefore, this paper uses the finite element method to solve the stray loss of components in the time-varying magnetic field. At the same time, the core losses of the magnetic shielding are solved. In addition, the position of the tap is considered, and the proposed stray loss model has the temperature factor, which can improve the accuracy of the simulation results. Finally, the short circuit test experiment is carried out in the 350 MVA three-phase five-limb power transformer. The proposed models and material parameters are verified by the experimental results.

An Efficient and Stable Embedded Multi-U-Shaped Column Rotary Transformer

Abstract: Inductively coupled power transfer (ICPT) technology can be used to solve the problems of high friction loss, overheating and low stability caused by conductive slip rings on rotating power supply equipment. An improved embedded multi-U-shaped column rotary transformer (EMUCRT) based on the ICPT and spliced core structure is proposed in this article. It has a higher coupling coefficient and can transmit power more efficiently and stably due to the primary magnetic core is embedded inside the secondary magnetic core. Compared with the one-piece core structure, the spliced type is more flexible due to its loose magnetic core arrangement. Its primary coil can still transmit energy stably after offset by a certain distance, so the structure has good anti-misalignment ability. On the basis of analyzing its magnetic core arrangement and magnetic circuit model, the optimal magnetic core specifications and quantities of primary and secondary side are obtained by theoretical calculation and simulation. In order to verify the high efficiency, rotational stability and anti-misalignment characteristics of the structure, an experimental prototype was built. The results show that EMUCRT can transmit energy efficiently and has good rotational and offset stability.

Neutron imaging for magnetization inside an operating inductor

Abstract: Abstract Magnetic components are key parts of energy conversion systems, such as electric generators, motors, power electric devices, and magnetic refrigerators. Toroidal inductors with magnetic ring cores can be found inside such electric devices that are used daily. For such inductors, magnetization vector M is believed to circulate with/without distribution inside magnetic cores as electric power was used in the late nineteenth century. Nevertheless, notably, the distribution of M has never been directly verified. Herein, we measured a map of polarized neutron transmission spectra for a ferrite ring core assembled on a familiar inductor device. The results showed that M circulates inside the ring core with a ferrimagnetic spin order when power is supplied to the coil. In other words, this method enables the multiscale operando imaging of magnetic states, allowing us to evaluate the novel architectures of high-performance energy conversion systems using magnetic components with complex magnetic states.

Selecting the Best Magnetic Core Geometry

Abstract: Selecting the best core geometry for a given application can be challenging given all the options available. For high-frequency applications using ferrite and other low loss materials, many different shapes are available from core manufacturers. For power electronics applications, frequencies are not constrained to power line frequencies leading to more complex core designs. Proximity effects, nonlinear core excitation, and sensitivity to frequency are just some effects to consider for good designs. Whether designs are intended for 50 Hz or 100 kHz, the basic design equations are the same.

Research on Motion Characteristics of Circuit Breaker Electromagnet in Different Conditions

Abstract: The electromagnet is an important component of the circuit breaker operating mechanism. The stable work of the circuit breaker depends on the normal work of the electromagnet. In order to study the operation characteristics of the circuit breaker electromagnet, an electromagnet simulation model is established to analyze the action of the moving iron core and the coil current under the normal operation of the electromagnet. On this basis, the change of the moving iron core and the coil current under typical faults, such as the moving iron core jamming and coil voltage reduction, has also been studied. What’s more, the changes in the coil current under normal and fault conditions have been analyzed.

Magnetic Core Design for CRAFT NNBI Core Snubber

Abstract: The CRAFT project is a preliminary technology verification facility for Chinese next-generation magnetic nuclear fusion experimental device. The neutral beam injection system, as an important device for tokamak plasma current drive and auxiliary heating, is an important part of the CRAFT project. The core snubber is an important protection device to avoid breakdown damage during the operation of the neutral beam source. It can effectively suppress the surge current, absorb the arc energy, and weaken the EMI impact on nearby equipment. In this paper, the installation space and operating state of the core snubber are used as the initial conditions, and the core design of the core snubber is completed with the FBO method. Finally, the core parameters that meet the requirements of the physical scheme are obtained. In addition, by comparing the parameters of the four magnetic core materials to be selected, the silicon steel material with larger magnetic flux density variation and better square shape is selected as the magnetic core winding material of the snubber.

A Magnetic Shielding-Type PEC Sensor With a Canister Structure and Magnetic Core

Abstract: The pulsed eddy current (PEC) technique exhibits considerable benefits over conventional eddy current techniques. The structure and dimensional parameters of PEC sensors considerably influence the PEC systems. Conventional PEC sensors are susceptible to background noise of a magnetic excitation field. To strengthen the magnetic gathering ability and improve detection sensitivity, a magnetic shielding shell structure was introduced to PEC sensors. In this study, a novel canister structure and magnetic core-based PEC sensor with magnetic shielding was designed. Finite-element simulation and experimental study were performed subsequently to optimize the design. A 3-D finite-element simulation model was established according to the eddy current detection mechanism and electromagnetic shielding principle. The influence of the PEC sensor structure and size on its detection performance was observed. Next, a 2-D axis-symmetric model was established, and the size of this PEC sensor was optimized by using the orthogonal approach. The results revealed that the detection performance of this PEC sensor could be improved by incorporating an appropriate magnetic shielding mechanism and through the optimization of the sensor size. The research results show that compared with the PEC sensor without magnetic shield, the PEC sensor with magnetic shield developed in this article can obtain higher signal amplitude and can be better applied to surface and subsurface defect detection.