Auxiliary Permanent Magnets Research Articles

Magnetic Force Performance of Hybrid Multisurface HTS Maglev System With Auxiliary Onboard PMs

The vertical levitation force, guidance force, and magnetic stiffness values, and thus the loading capacity and movement stability of high-temperature superconducting (HTS) Maglev systems, are aimed to be increased in this study by using auxiliary permanent magnets (PMs) in the onboard unit together with the multisurface HTS-permanent magnetic guideway (PMG) arrangement (hybrid multisurface arrangement). First, the magnetic levitation force, guidance force, and stiffness performances of the hybrid multisurface arrangement were investigated at different field cooling heights (FCH). Then, to compensate for the negation of instability that results from the higher repulsive force between the onboard PMs and the PMG and to obtain an optimal magnetic field medium, we have changed the vertical position of the auxiliary onboard PMs (Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PM</sub> ) to Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PM</sub> = 0, 2, and 4 mm, at the cost of a bit of adecrement in the vertical levitation force. The bigger levitation force, together with the guidance force values for FCH = 25 mm and Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PM</sub> = 0 mm, indicates that the hybrid multisurface HTS–PMG arrangements are beneficial to increasing the practical applicability of Maglev systems.

Investigation of the magnetic separation performance of a low-intensity magnetic separator embedded with auxiliary permanent magnets

Low-intensity magnetic separators (LIMSs) comprise one of the most widely employed magnetic separation equipment. It is worth studying how to reduce magnetic flux leakage and significantly improve magnetic induction. Typically, auxiliary permanent magnets (APMs) are embedded in the main permanent magnets (MPMs) to increase the magnetic induction. In this study, the effect of the matching relationship between the widths of the MPM and APM and the height of the APM on the magnetic field distribution and magnetic separation performance are investigated. The wider the width of the MPM is, the wider the area of the relatively high magnetic induction intensity. Therefore, increasing the width of the MPM can effectively capture farther magnetic particles, which can effectively improve the magnetic separation performance. In addition, when the size of the MPM is constant, although the height of the APM is increased, the magnetic induction is improved less significantly. The research findings indicate that the height of the APM is approximately two-thirds of that of the MPM, so a satisfactory magnetic field distribution and magnetic separation performance can be obtained. Furthermore, to verify whether APM-LIMSs have advantages, a conventional low-intensity magnetic separator (CON-LIMS) without MPMs was designed. The magnetic field distribution and the effect of important parameters (remnant flux density, drum/tank distance, feeding speed and particle size) on the separation recovery are systematically compared and investigated through detailed computational simulations corresponding to the operating conditions. All the comparison results indicate that embedding APMs in the gaps of MPMs significantly expands the area of relatively high magnetic induction, which can ensure that there is still a strong magnetic force in the area far from the surface of the drum, thereby significantly improving the separation performance. Therefore, APM-LIMSs can capture a wider range and finer particle size. Moreover, APM-LIMSs can select low-cost, ferrite, permanent magnets and set a higher feeding speed and a wider drum/tank distance, thereby significantly increasing the processing capacity while ensuring a high separation performance.

Analysis and testing of a superconducting maglev submersible cryogenic liquid pump

This paper studies a superconducting maglev submersible cryogenic liquid pump (CLP) using superconducting magnetic bearing (SMB). A new structure is proposed for the self-stability of high-temperature superconducting magnetic levitation, and the compact structure of disk motor-pump. The rotor of the axial-flux disk motor is connected with a centrifugal impeller to form an impeller-rotor of the proposed superconducting CLP. Supported by a SMB system, the impeller-rotor rotates frictionlessly with self-stabilisation as a suspension rotor. The SMB system includes a radial-type SMB, an auxiliary permanent magnet bearing, and an electromagnetic bearing composed of the stator and the rotor of disk motor. Theoretical calculations and experimental measurements are performed to examine the axial and radial levitation force behaviours of the SMB system. Then, a kinetic model of the suspension rotor is established and analysed to assure force balance and stable levitation. Finally, a prototype pump is fabricated and an experimental setup for liquid nitrogen transmission is constructed for validation purposes. The experimental tests on the pump head and the flow rate are carried out, which demonstrate the effectiveness of the proposed superconducting maglev submersible CLP.

Design and analysis of a novel claw‐shaped modular stator relieving‐DC‐saturation doubly salient machine with 3D complementary magnetic circuit

Here, a novel DC-excited doubly salient machine with a claw-shaped modular stator and three-dimensional (3D) complementary magnetic circuit is proposed for wind power generation application. The key is to artificially construct a 3D complementary structure to suppress torque ripple and employ auxiliary slot-opening PMs to relieve DC-saturation in the stator core and improve overload capability. The novel 3D complementary structure provides an alternative magnetic path for the main flux, so the flux leakages in the air gap at open-circuit position are effectively cancelled, and the flux in the yoke remains relatively constant. Hence, the output torque ripple is suppressed. Furthermore, the saturation issue in the stator is solved with auxiliary permanent magnets which have opposite magnetization direction to that of DC field excitation. Therefore, the torque capacity of the machine is improved. Here, the machine structure and operation principle are introduced, and a 2D equivalent model is also developed to replace the 3D model to improve the calculation efficiency. Multi-objective optimization algorithm is developed to improve the performance of this new machine. The validity of machine design is finally verified with 2D and 3D finite element analysis.

Analysis and Design of a New Relieving-DC-Saturation Transverse-Flux Tubular Motor With Complementary Magnetic Circuit

Due to the flux leakage and large detent force, the thrust force ripple of transverse-flux linear motor is relatively large, which restricts its further application. Also, the field of most existing transverse-flux machines is hard to be altered and regulated considering the permanent magnet (PM) excitation. Therefore, to suppress the force ripple and strengthen the flux regulation capability of transverse-flux machines, a novel hybrid excitation transverse-flux tubular motor with complementary structure is proposed in this article. The key is that a complementary and parallel structure is constructed in this motor, and hybrid excitation of both dc windings and small auxiliary PMs installed at opening of the slot is adopted in this motor as well. In addition, unequal teeth design of dc winding and ac winding is also employed to increase the thrust force density. Finite element calculation results verify the effectiveness of the proposed machine.

Modeling of the dynamics of a superconducting maglev in the mixed state

We studied the levitation of a YBa2Cu3O7 (YBCO) melt-textured superconducting specimen above a closed path of permanent magnets. The superconductor was magnetized with an auxiliary permanent magnet before brought to the path of magnets. This way, the superconducting levitation in the mixed state was achieved. The vertical and horizontal forces acting on the superconductor were calculated by means of two models. One model considers that the superconductor is in the Meissner state and assumes that it is possible to take into account the demagnetizing field by using a single average parameter. The second model considers that the superconductor with trapped field behaves as a permanent magnet with a uniform magnetization. The total force on the superconductor in the mixed state is result of the superposition of these two contributions. In order to validate the model, the height of levitation and the frequency of horizontal oscillations were measured. Both variables were then calculated with the model fed with experimental information. The calculated values were in agreement with the measured ones.

In-situ post-assembly magnetization of large rare-earth permanent-magnet machines

Auxiliary permanent magnet generator (PMG) represents an essential part of the large steam generator excitation system. It provides energy for main exciter (rated power 1600 kVA) which supplies excitation for steam generator (rated power 300 MW). While auxiliary PMG is out of service, its permanent magnets are demagnetized. In order to put auxiliary PMG into operation, magnetization of permanent magnet poles is needed. This paper presents a method for in-situ post-assembly magnetization (PAM) of rare-earth PMG by applying DC current to all three phases of its stator windings. Magnetization process is performed in the power plant, and all equipment used in experiment is readily accessible to plant maintenance personnel (transformer, rectifier, circuit breaker, cables, etc.). The main advantage of this technique is that magnetization is performed without demounting the PMG off the main rotor shaft, and as a result, generator overhaul duration is significantly reduced, and magnetization costs are decreased. Throughout the procedure, magnetizing currents, voltage on PMG stator terminals and magnetic induction (flux density) are measured. Prior to magnetization, DC currents, current pulse duration and rotor position are calculated. Based on the calculated values, the temperature rise in stator windings has to be checked. The technique is validated through case study in the real power plant at the PMG, rated power 35 kVA, which was successfully magnetized. Subsequently, the simulation is performed, in order to determine the unknown parameters of the equipment used.

Pole Optimization and Thrust Ripple Suppression of New Halbach Consequent-Pole PMLSM for Ropeless Elevator Propulsion

Permanent magnet linear synchronous motors (PMLSM) has the advantages of high speed, high thrust density, high power density, high power factor and high reliability. In order to save permanent magnet (PM) materials and reduce magnetic leakage, a new type of PMLSM with Halbach consequent-pole (HCP) structure is presented, which has great potential for application to the ropeless elevator system. By using extensive finite element analysis (FEA), the electromagnetic properties of the proposed HCP-PMLSM, including magnetic field, back electromagnetic force (back-EMF), thrust force and cogging force are simulated and compared with the consequent pole PMLSM (CP-PMLSM) and surface-mounted pole PMLSM (SP-PMLSM). The comparison results show that the proposed HCP configuration can reduce substantial PM material and increase the air-gap magnetic field effectively. Then, the influence trend of HCP parameters such as pole thickness, pole width ratio, auxiliary PM width and magnetism angle, are studied and analyzed for evaluating the output performance in HCP-PMLSM. On this basis, Response surface method (RSM) is employed to optimize the HCP parameters with the target of maximum average thrust, minimum thrust ripple, and highest PM utilization. Furthermore, a double-sided pole shift method was proposed to significantly suppress the thrust fluctuation of HCP-PMLSM. Lastly, experimental results are provided to verify the investigation.

Analysis of an on-line superconducting cryofan motor for indirect cooling by LH2

This work relates to the study of an electrically powered cryofan for circulating closed-loop cooling helium gas for superconducting applications with the following features:- Absence of any seal that can leak the pumped fluid or provide a path for heat transfer and require maintenance and/or is prone to failures.- The use of high temperature superconducting (HTS) stacks on the fan-rotor that, below critical temperature, can be magnetized contributing to the driving torque.The absence of electrically connected equipment as well as the lack of any seal, makes this arrangement especially suitable for reliable cryogenic helium gas circulation. Because HTS stacks cannot provide magnetic flux above Tc, during the initial stages of operation, in the presented study we analyse the torque that will be provided by the passive iron components of the machine (reluctance torque, due to the saliency of the rotor) and by auxiliary permanent magnets or alternatively magnetizing coils.

Lateral Position Effect of Auxiliary Permanent Magnets on the Magnetic Force Properties of Cylindrical YBCO

The magnetic levitation force (MLF) and the guidance force (GF) should be improved for loading capacity and stability of Maglev systems, respectively. Although there are some ways to increase these properties, using of auxiliary onboard permanent magnets (PMs) can be considered as the most efficient one. The auxiliary PMs increase the MLF significantly but, at the same time, decrease the GF. We have searched a solution to overcome this problem in this study. Firstly, we have determined the optimum vertical positions of the auxiliary PMs and then we have investigated the vertical levitation force and lateral guidance force of hybrid Maglev system depending on lateral position of auxiliary PMs in different cooling heights (CHs). A cylindrical YBCO superconductor, fabricated by a top seeding method with the diameter of 45 mm and the height of 15 mm, was used as a high-temperature superconductor (HTS). The maximum increment rate in MLF and the minimum decrement rate in GF were observed as 277 and 54 %, respectively. The increment in MLF was obtained five times more than the decrement in GF, and this reality points out that the results of this study can be useful for improving the loading capacity and thus enhancing the practical applicability of Maglev systems.

Novel Structure of Three-Axis Active-Control-Type Magnetic Bearing for Reducing Rotor Iron Loss

Magnetic bearings (MBs) are useful for suspending the rotor shaft of a high-speed, high-output motor because they can do so without mechanical contact. In [2] , we have proposed a three-axis active-control-type MB (3-axis AMB) with a cylindrical rotor whose diameter is equal to that of the rotor of a radial MB (RMB) or a motor. The proposed 3-axis AMB integrates an RMB and a thrust MB in one unit. However, the assembly of the conventional 3-axis AMB is complex, and the rotor iron loss is large. Thus, in order to simplify the assembly of the 3-axis AMB and to reduce rotor iron loss, this paper discusses a novel structure for the 3-axis AMB in which small auxiliary permanent magnets (PMs) are inserted in the radial winding slots. The suspension force and the rotor iron loss of the proposed device are evaluated by 3-D finite-element analysis in comparison with a 3-axis AMB without small auxiliary PMs.

Influence of Auxiliary Permanent Magnet on the High-$T_{\rm c}$ Superconductive Hybrid Maglev System

The high-Tc superconductive (HTS) hybrid Maglev with the auxiliary permanent magnet (PM) is a useful method to improve the system load density and stiffness. The auxiliary PM changes the magnetic circuits and increases the instability of the Maglev system. To investigate the levitation performance, different HTS hybrid Maglev arrangements involving PM and bulk HTS were tested above the permanent magnet guideway. Some useful conclusions and reference for relative design can be found from the experimental results and analyses.

Profile control of large-area rectangular plasma in a modified-magnetron-type RF discharge

A large-area rectangular modified-magnetron-type (MMT) radio frequency (RF) plasma source is newly developed and the properties are investigated in detail for producing a large-area uniform plasma. A quite uniform plasma with density variation less than several percent is produced in front of the rectangular substrate of 830×650 mm 2. The spatial plasma uniformity is controlled not only by employing an upper auxiliary electrode but also by putting permanent magnets on the auxiliary electrode in several patterns. We now produce more uniform plasma by using auxiliary permanent magnets put on the upper auxiliary lid electrode.

Low temperature growth of rutile TiO 2 films in modified rf magnetron sputtering

Low temperature (≤300°C) growth of rutile TiO 2 films with high refractive index which is equal to bulk TiO 2 crystal was achieved by using a modified sputtering method. Depositions were carried out in rf magnetron sputtering apparatus equipped with an auxiliary permanent magnet just under the grounded electrode. The as-deposited films showed rutile polycrystalline structure and fine surface morphology indicating higher densification. Remarkable changes in composition, total current and energy of incident ions were presented at a Ar–O 2 total pressure of 2.7 Pa. The rutile phase grows in a modified sputtering method in contrast with anatase phase growth in conventional sputtering apparatus.

Up-grading a 4.7-cm-period plane electromagnetic undulator

Electromagnetic undulators have a number of advantages over permanent-magnet undulators. They are less expensive to fabricate and their field is easily regulated by changing the current, without requiring a complex and expensive precision system for changing the undulator gap. Their main weaknesses are that they require a large power supply and that the field is limited due to yoke saturation mainly because of large axial stray fluxes, particularly in simple constructions. Modernization of a 4.7-cm-period, 20-period long plane electromagnetic undulator of simple design is described. Samarium-cobalt permanent magnets were used to increase the field and decrease power consumption. They were placed between adjacent rings (with opposite sign of field) and while increasing the working field they decreased saturation of the iron yokes. Small lateral displacements of permanent magnets were used to equalize field amplitudes in half periods of the undulator with 0.1% accuracy. Matched input and output to and from the undulator, respectively, were formed by means of auxiliary permanent magnets and special magnetic screens

Deposition of High-Quality TiO 2 Films by RF Magnetron Sputtering with an Auxiliary Permanent Magnet

RF magnetron sputtering with an auxiliary permanent magnet was applied for the deposition of TiO2 films. An auxiliary magnet was installed under a grounded electrode and the magnetic field strength was intensified in the whole discharge space. The film prepared by this sputtering apparatus showed a high value of the refractive index equal to that of bulk TiO2 crystal. The results of several diagnostic techniques showed characteristic changes in the discharge structure. It was shown that a high current of substrate-incident ions brings about growth of high-quality TiO2 films.