Permanent Magnet Guideway Research Articles

Levitation Force Characteristics of High-Temperature Superconducting Bulks in a High Magnetic Field

The levitation force of high temperature superconducting (HTS) bulks can be enhanced by raising the strength of the external magnetic field. As to the field of HTS magnetic levitation (maglev), many researchers have also obtained this conclusion by levitation experiments above a permanent magnet guideway (PMG). However, the experimental results have limitations because the magnetic field above the PMG is relatively low, around 0.4 T at the 15 mm working height. In order to obtain more comprehensive levitation force characteristics of HTS bulks, it is necessary to carry out more experiments in high magnetic field. In this paper, the effects of magnetization angle and external field gradient on the levitation force of an HTS YBCO bulk which was manufactured with a top-seeded multi-seeded melt-textured process were studied. We set up a levitation force measurement system based on a 5-T Cryogen-Free Magnet (CRY-CFM-5 T-300-H3, Cryogenic Limited). The HTS bulk was cooled by liquid nitrogen in zero-field-cooling condition, and the external magnetic field was enhanced from 0 to 3 T. The HTS bulk was rotated 30° each time and finally rotated to 90°. Experiments show that the levitation force decreases from θ = 0° to 90°, where θ is the angle between the upper surface of the HTS bulk and the horizontal plane. The conclusion that the levitation force increases with the increase of the external magnetic field gradient in high magnetic field was also further confirmed.

Strategies to improve the dynamic levitation performance of superconducting maglevs against force decay and disturbance

In the design of maglev systems, the levitation force determines the levitation height and the dynamic stability associated with potential vibrations, especially the offset of the levitation point relative to the working point. However, such two key parameters are often antagonistic: a relatively low dynamic stability comes with a high levitation force, whereas a relatively low levitation force can come with a high dynamic stability. In this paper, we will discuss several strategies to deal with this problem by means of a two-dimensional numerical model based on Newton's second law and Maxwell's equations together with a power-law constitutive relation. The dynamics of maglev systems consisting of a bulk high-temperature superconductor and a Halbach-type permanent-magnet guideway with soft ferromagnets are analyzed. The results show that the drift phenomenon occurs in both vertical and lateral directions triggered by a transverse disturbance, and preloading can alleviate such a phenomenon, but this will lead to a reduction in the levitation force. Improved preloading is effective in enhancing the levitation force without sacrificing the dynamic stability. In some systems, the levitation force and dynamic stability can be further improved by adjusting the soft ferromagnets to an appropriate location in the guideway. Moreover, some guidelines on how the superconducting part should be designed are provided in order to overcome the technical difficulty and reduce the material consumption while at the same time maintaining the dynamic levitation performance.

Technical Feasibility Study of an E-Shaped Electromagnetic Guideway for HTS Maglev

High temperature superconducting (HTS) maglev technology has been developed for more than two decades. Permanent magnet guideway (PMG) has been always used for the rail of a HTS maglev system so far. For the long distance HTS maglev system, PMG has some disadvantages in practice. In last few years, we carried out studies to investigate the feasibility of using electromagnetic guideway (EMG) for a HTS maglev system. EMG is not only more reliable, but also more controllable and flexible. We have proposed an E-shaped electromagnet that could be the basic element for building an EMG with good controllability and flexibility. The geometrical and circuitry design of the E-shaped electromagnet were first suggested through theoretical magnetic circuit analysis. The design then was examined and optimized by computer simulation. Afterward, we made a prototype and conducted several levitation tests to verify the design with a high precision measuring platform. In this article, the performances of the prototype with different exciting modes and different dimensions are reported and discussed.

Determination of magnetic levitation force properties of bulk MgB2 for different permanent magnetic guideways in different cooling heights

Abstract In our study as different from the literature, the magnetic levitation force between a bulk MgB2 and two different permanent magnetic guideway (PMG) arrangements, which are Halbach and Conventional PMGs, were investigated in different cooling heights (CHs) and Field-Cooled (FC) condition at the temperatures of 37 K and 33 K. The cylindrical bulk MgB2 superconductor was fabricated by in-situ solid state reaction process with the diameter of 18 mm and the height of 5 mm. The XRD data indicates well developed MgB2 phase and the Jc value was obtained as 68 kA/cm2 at 30 K in the self-field. Experimental results show that MgB2 bulk above the Halbach PMG can exhibit better load capability at all the cooling heights between the bulk MgB2 and the PMG due to a more suitable magnetic field distribution. The maximum levitation force for Halbach PMG corresponds to 16.86 N whereas the conventional PMG shows 9.02 N at 37 K in cooling height of 77 mm. Additionally, the maximum levitation force increases while the CH increases because flux exclusion is more effective for larger CHs. It is considered that the experimental results obtained in study are very useful for future Maglev applications, because there are limited number of studies on magnetic levitation force of MgB2 bulk for different MgB2-PMG arrangements.

Modeling and identification of the hysteresis nonlinear levitation force in HTS maglev systems

High-temperature superconducting (HTS) maglev has great potential in the field of high-speed transportation due to its capability for passive stabilization. The levitation force between the bulk HTSs and the permanent magnet guideway is a significant parameter relating to operational safety and comfort. This force has an obvious hysteresis nonlinear characteristic, which can be represented by nonlinear stiffness and damping. The stiffness and the damping are functions of vertical displacement and velocity, respectively. The vibration velocity of a HTS maglev vehicle can at times exceed 100 mm s−1, but the existing levitation force test methods are almost quasi-static. These methods are unable to accurately measure the damping characteristic of the maglev system. In this paper, a viscoelasticity model is introduced to describe the dynamic force. The parameters in the model are identified using the least square method based on the vibration response of the HTS maglev system. Meanwhile, the effectiveness of the model and identification method are tested by numerical simulations. The hysteresis loops derived from the motion theory coincide with the practical ones. Finally, the method is applied to identify the parameters of hysteresis nonlinear levitation force in a previous experiment with dampers. Based on the established hysteretic model, the dynamic characteristics of the HTS maglev system can be well presented.

Temperature characteristics of bulk YBCO exposed to high frequency fluctuant magnetic field in high-TC superconducting maglev system

In high-temperature superconductor (HTS) Maglev system, the permanent magnet guideway (PMG) can't be formed by the whole permanent magnet (PM), which results in the existence of multiple PM splicing slots in the PMG. Moreover, this kind of splicing gap will become bigger with the longer service time of PMG. In addition, due to material inhomogeneity and magnetization difference inside a single PM and there will be fluctuation in magnetic field (MF) above PMG. The fluctuation may have a great impact on the efficient and stable operation of the Maglev system. This paper focuses on the influence of fluctuant MF on the temperature rise inside bulk HTS, including the internal loss caused by cooling height (CH), working height (WH) and frequency of MF change. Finally, the HTS Maglev system is analyzed from temperature rise inside the bulk HTS. The results and analyses of this article are useful for the application of bulk HTSs in the Maglev system.

Optimization study of the Halbach permanent magnetic guideway for high temperature superconducting magnetic levitation

Due to the combined advantages of no-contact friction and self-stable levitation, high temperature superconducting magnetic levitation (HTS Maglev) has significant potential for rail transit applications. In order to further improve the carrying capacity of the HTS maglev system, it is necessary to optimize the permanent magnet guideway (PMG). In this paper, the original Halbach PMG was optimized and a new PMG with better performance was designed and manufactured. The magnetic field and magnetic forces were calculated by the finite element method, and the size and magnetization direction of each PM in the PMG were optimized. Then, the magnetic field above the optimized PMG were measured and compared with the original Halbach PMG as well as the levitation and guidance force of the bulk high temperature superconductors. Experimental data show that the magnetic field above the optimized PMG is effectively enhanced and the levitation and guidance force of the superconductors increase by 12.2% and 11.3%, respectively. This study can provide the foundation for the further optimization of PMGs and the research of large load HTS Maglev technology.

Comparative study between electromagnet and permanent magnet rails for HTS maglev

In this study, we investigated the magnetic levitation characteristics of a high-temperature superconducting (HTS) bulk with both permanent magnet guideway (PMG) and electromagnet guideway (EMG). Trying to have the magnetic fields of the two kinds of guideways with a similar structure, then the central magnetic flux density Bz and unit magnetomotive Fu were selected as the evaluation indexes respectively for the comparative study. Different magnetic field characteristics on magnetic levitation performance were studied, such as the gradient of magnetic flux density and magnetic flux density component in different directions. Several experiments were carried out at different magnetic field conditions by changing the exciting current of EMG or replacing different PMG specimens. The experiments were conducted with a high-precision force-measuring platform. The experimental results show that the EMG has several different characteristics as compared with PMG. As a result, the magnetic levitation performance is related to the gradient of magnetic flux density as well as the directional magnetic flux density components. The structure of the magnetic field also has great influence on the performance. The results will be helpful for further study of the properties of HTS maglev and provide guidance for the subsequent EMG design.

Magnetic Characteristics of Nd-Fe-B Permanent Magnets at High Temperature and the Effect of Temperature on High-Temperature Superconducting Levitation Performance

In the practical application of high-temperature superconducting (HTS) magnetic levitation, the influence of ambient temperature on its performance is mainly reflected in the change of magnetic characteristics of the permanent magnet guideway (PMG). In order to investigate the magnetic characteristics of the PMG at high temperature and the influence of temperature on the levitation performance of HTS bulk above, we studied the magnetic characteristics of three kinds of PMG and six kinds of single permanent magnet (PM) in the temperature range from room temperature to 85 °C. Furthermore, we investigated the effect of this variation on the levitation performance of HTS bulk under a zero-field-cooling condition. The results show that the N-S-S-N-type PMG-H has better magnetic field stability than the Halbach PMG-I and the N-N-S-S-type PMG-J at high temperature. The levitation force of HTS bulks decreases with the increase of the PMG temperature. The variation range of levitation force is larger than that of magnetic field of PM, but absolute values under 55 °C are small. This work provides a reference for the engineering PMG optimization of HTS magnetic levitation.

A Force Measurement System for HTS Maglev Studies

An improved force measurement system was developed for investigating high-temperature superconducting (HTS) maglev properties. The measurement system consists of assorted sensors, a 3-D sliding platform, a mechanical drive with automatic control software, and a data collecting and processing software. This system features high precision, instant measurement at the movement of the targeted HTS bulk, synchronous measurement of levitation force and guidance force, and the magnetic field. This system can be used for studying the interaction behavior between an HTS bulk and a permanent magnet guideway (PMG) or an electromagnetic guideway (EMG) of different shapes and sizes. It can realize arbitrary 3-D complex curvilinear motions. This system was built with a flexible platform and high precision force and distance sensors. As a result, the magnetic levitation characteristics of an HTS bulk above a magnet guideway can be precisely investigated with this system. In general, the aforementioned functions all have been verified by experiments.

Modeling of High-Tc Superconducting Bulk using Different Jc–T Relationships over Dynamic Permanent Magnet Guideway

The linear temperature dependence of critical current density Jc∝((Tc-T)/(Tc-T0)) and the nonlinear functions of Jc∝(1-(T/Tc)2)α with the exponent α equal to 1, 3/2, and 2 are used to calculate the dynamic levitation force, the temperature distribution, and the current density distribution of the high-temperature superconducting (HTS) YBaCuO bulk over a permanent magnetic guideway (PMG). The calculations were based on the H-formulation and E–J power law. The model of the HTS bulk and the PMG has been built as a geometric entity by finite element software. To simulate the magnetic field fluctuation caused by the PMG arrangement irregularity, a small amplitude vibration in the vertical direction is applied to the PMG during the calculations. Both the low vibration frequency of 2 Hz and the high vibration frequency of 60 Hz are analyzed as the representative converted linear speeds of 34 km/h and 1018 km/h for magnetic levitation (Maglev) application. We compared the electromagnetic-thermo-force modeling with the experiments and the previous model without considering the thermal effect. The levitation force computed by the Jc–T relationship, in which Jc is proportional to (1-(T/Tc)2)2, is found to be in best agreement with the experimental data under quasi-static conditions. This work can provide a reference for the HTS electromagnetic-thermal-force coupling reproduction method of HTS Maglev at high speed.

Investigation of magnetic force properties between different PMGs and multi-seeded YBCO superconductors with different seed distances

The magnetic levitation force in vertical direction and guidance force in lateral direction should be increased for enhancing the loading capacity and stability of Maglev systems, respectively. In this study, we have produced multi‒seeded YBCO (YBa2Cu3O7) superconductors with two seeds and investigated the effect of seed distance on the vertical levitation force and lateral guidance force properties by using different permanent magnetic guideway (PMG) arrangements. Although there are studies in literature related to different distance, orientation and angle of seeds; there is no detailed study investigating the effect of seed distance on the vertical and lateral magnetic force properties of Maglev systems depending on different types of PMGs. In this study, after the sample fabrication, the optimum PMG arrangement were determined by using numerical simulation to obtain magnetic flux density distribution. It is determined that both maximum levitation and guidance force values firstly increased with increasing the seed distance from 0 to 4 mm and then related forces decreased with increasing the seed distance from 4 to 16 mm but still keep the higher force values than the sample with the seed distances of 0 mm. This situation is clarified as the increasing of the seed distance to an optimum value enhances both the levitation and guidance forces simultaneously and this is very important for levitation force applications because it causes to easy control of the Maglev system in vertical and lateral directions.

Numerical Simulation and Experimental Analysis on the AC Losses of HTS Bulks Levitating Under a Varying External Magnetic Field

Alternating current (AC) loss occurs when the high-temperature superconducting (HTS) maglev running on a permanent magnetic guideway (PMG) with a varying field. The running stability and safety of the HTS maglev vehicle will be influenced by the AC losses, which are closely related to the magnetic field fluctuation of the PMG and the levitation characteristics of HTS bulks. In order to study the AC losses of the HTS bulk under a varying field with different frequencies and amplitudes, numerical simulation and experimental analysis are employed. The simulation model was built by COMSOL Multiphysics with the partial differential equations module and heat transfer module. The experimental analysis of AC losses was designed based on a calorimetric method. The experiments are based on an HTS maglev dynamic measurement system, in which the rotational velocity of the PMG and working height of the HTS bulks are changed for simulating the experimental conditions of different frequencies and amplitudes of the AC field. And, the AC losses of HTS bulks are deduced from the evaporation amount of the liquid nitrogen. The simulation findings are consistent with the experimental phenomena qualitatively, which not only verify the rules of frequency and amplitude, but also the availability of the numerical simulation method. Moreover, the findings provide important hints for the future design of the HTS maglev systems.

Dynamic Simulation of the HTS Maglev Vehicle-Bridge Coupled System Based on Levitation Force Experiment

In this paper, we built a high-temperature superconducting (HTS) maglev vehicle-bridge coupled system model by Universal Mechanism (UM) software, and analyzed the vertical dynamics. The UM model is composed of two parts, the train subsystem involved three vehicles, and the flexible bridge with simple-supports. In the UM modeling system, the expression of levitation force and the parameters related to the maglev vehicle-bridge were indispensable. The levitation force of maglev vehicle was described by an exponential analytical expression simplified by the experimental results of four YBCO bulks above a Halbach permanent magnetic guideway. The parameters related to the maglev vehicle-bridge are based on experimental prototype. Based on the UM model, the vertical dynamic was simulated and analyzed with different bridge spans under different operating velocities. This subject is a basic study for understanding the unique dynamic characteristic of the HTS maglev vehicle-bridge system. The simulation results provided reference for the further design of the HTS maglev vehicle-bridge coupled system in different speed ranges.

Magnetic Field Test on an Electromagnetic Turnout Prototype System for High-T c Superconducting Maglev

Due to the strong magnetic force between segments of the permanent magnet guideway (PMG), the unmovable electromagnetic turnout becomes one of the most possible choices for high-temperature superconducting (HTS) maglev systems. Meanwhile, it has advantages of quicker response and smaller volume compared with mechanical turnout. A complete turnout system is vital for further evaluating feasibility. Based on the previous studies in ASCLab of Southwest Jiaotong University, a complete electromagnetic turnout prototype system is introduced in this article, which consists of two electromagnets, a Halbach type PMG, a control system, and a maglev vehicle model with a single-domain YBaCuO cylindrical bulk superconductor. In order to guarantee the stable running of vehicle at the turnout area, electromagnets are necessary to provide a similar magnetic field compared with the normal Halbach PMG. Based on the system, the measurement on the magnetic field was done and indicates that the electromagnet could replace permanent magnets of guideway to create a similar magnetic field distribution. The magnetic field experiment on this prototype system further certifies the applicability of the Halbach electromagnetic turnout. For future HTS maglev transportation, the electromagnetic turnout could be widely used in low-speed application such as railway station, switchyard, and laboratory.

Magnetic levitation and guidance performance of Y–Ba–Cu–O and Gd–Ba–Cu–O bulk superconductors under low ambient pressure

The high-temperature superconducting Maglev-evacuated tube transport (HTS Maglev-ETT) system has significant potential for practical applications. In order to employ HTS bulks in an ETT system, it is necessary to study the magnetic levitation and guidance performance of bulk superconductors under low ambient pressure conditions that are representative of those inside the tube. As a result, we have investigated the Maglev performance of Y–Ba–Cu–O (YBCO) and Gd–Ba–Cu–O (GdBCO) single grain, bulk superconductors under different ambient pressures of 100 kPa, 60 kPa and 20 kPa using a bespoke pressure-controlling platform, in which the superconductors were positioned above a Halbach permanent magnet guideway. The levitation forces under conditions of field-cooling (FC) and zero-field-cooling (ZFC) have been measured and analyzed. The guidance force for the FC case and the levitation force relaxation for the ZFC case were also measured. It was found from the experimental results that the Maglev performance of both types of bulk superconductor improves significantly by reducing the ambient pressure in their immediate working environment. The levitation forces of YBCO and GdBCO bulk superconductors were observed to increase by 11.6% and 4.4% in the case of FC, and by 20.3% and 13.7% in the case of ZFC, respectively, as the ambient pressure changed from 100 kPa to 20 kPa. An improvement of the guidance force and an inhibition of the levitation force relaxation were also observed for these materials. The supercooled liquid nitrogen cryogen in the low-pressure environment further reduces the temperature, which, in turn, increases the critical current density Jc of the bulk superconductors and improves their levitation performance. These results provide further evidence of the significant advantages of combining HTS Maglev with evacuated tube technologies as a key enabling feature of the HTS Maglev-ETT system. The data further indicate that YBCO bulk superconductors tend to be more sensitive to ambient pressure and temperature variation than GdBCO bulk superconductors. This difference essentially reflects the dependence of Maglev performance of HTS bulk superconductors on Jc when operating in a low-pressure environment.

Levitation Height Drifts of HTS Bulks under a Long-Term External Disturbance

High-temperature superconducting (HTS) maglev owns the capability of passive stabilization and has the potential to operate at a high speed with low energy consumption. However, the excitation caused by the irregular surface and inhomogeneous magnetic field of the permanent magnet guideway (PMG) will result in vibration between the superconductors and PMG, which could lead to some stability problems such as drift. To study the reliability of HTS maglev systems under a long-term disturbance, a tailored experimental device composed of a vibration table, a fixture, and HTS maglev model was employed. The effects of field-cooling height (FCH), external excitation frequencies, and amplitudes on the levitation height drift were investigated. It is found that under the same operating conditions, large excitation amplitude, high frequency, and low FCH would lead to a greater levitation height drift. There are three kinds of drift trends, i.e., downward, upward, or downward at first and then upward, and the phenomenon of drifting upward is more likely to occur under small excitation amplitude, high frequency, and low FCH conditions. Meanwhile, two simulation models employing the flux flow model and the flux flow and creep model were applied respectively. The simulation results show that the flux flow and creep model are more consistent with the experimental phenomena and the flux flow has a greater influence on the drift in the initial time period, while the flux creep has a slighter impact on the drift for a long time. These researches reveal the levitation height drift rules of the HTS maglev system and introduce proper simulation model for levitation height drift so that this work provides a reference for the design and safe operation of HTS maglev vehicles.

Guidance Force and Its Hysteresis of YBCO Bulks Under a Low-Pressure Environment

High temperature superconducting (HTS) maglev train running in the evacuated tube is a new kind of transportation with great potential. The HTS bulks are core component of the HTS maglev train, and its guidance performance is crucial to the ability of curve-passing. Therefore, it is necessary to study the guidance force of YBCO bulks under a low-pressure environment. Based on the test system of magnetic levitation characteristics under low-pressure environments, the super-cooling state of liquid nitrogen is realized by the method of evacuation. The guidance force of YBCO bulks moving laterally above a Halbach permanent magnetic guideway was measured under different pressure values (100, 60, 40, 20 kPa). Results show that decreasing pressure is beneficial to improve the guidance performance of YBCO bulks. When the field cooling height (FCH) is under 35 mm, the guidance force increases with the decrease of the pressure. However, when the FCH is more than 35 mm, the guidance force decreases with the decrease of the pressure. Furthermore, decreasing FCH and pressure value can decrease hysteresis of guidance force and enhance the lateral stability of the HTS maglev system.

Vibration Suppression of High-Temperature Superconducting Maglev System via Electromagnetic Shunt Damper

The high-temperature superconducting (HTS) maglev system is characterized with self-stable levitation, low energy consumption, and pollution-free operation, and it has been considered as a promising technology for implementing high-speed transport systems. But the previous studies have shown that the damping of such system is relatively low, which indicates the large-amplitude nonlinear vibration may occur easily under external disturbances and affect the long-term motion stability, operation safety, and comfort of HTS maglev in rail transit application. In order to suppress the harmful vibration, an electromagnetic shunt damper (EMSD) was designed and incorporated into the HTS maglev system. Compared with other systems which employ the EMSD to diminish the vibration, the HTS maglev system does not need to set up external devices to supply magnetic field for the damper, because the permanent magnet guideway (PMG) in this system is directly taken advantages of. The natural frequency of the damper is adjusted to a value close to that of the maglev system. In this way, the damper becomes most effective because the moving vehicle body and the circuit resonate simultaneously. The feasibility of the damper was demonstrated through systematic experiments, and the effects of different field cooling heights (FCHs) of the HTS maglev system on EMSD’s performance were experimentally studied as well. Also, how the change of resistors in the EMSD circuit affects its working efficiency was preliminarily explored in this work. The results show that under the definite external disturbance, the damper can effectively attenuate the acceleration of vibration, furthermore, and it is found that the damper works better in condition of lower FCH. Within the scope of our experiments, the EMSD with a resistor in lower resistance performs better as results have shown. This investigation indicates that the vehicle will run in a more smooth and comfortable way along the track with this damper. The work is important for the further practical application of the technology.

Effect Laws of Different Factors on Levitation Characteristics of High-Tc Superconducting Maglev System with Numerical Solutions

The interaction between the high-temperature superconducting (HTS) bulk and permanent magnet guideway (PMG) has been a topic among the existing HTS magnetic levitation systems. Up to now, the theories about the electromagnetic and force characteristics have been relatively consummated. Here, using the finite element model by COMSOL Multiphysics 5.3a, we investigated the impact of the intrinsic and external factors on the levitation characteristics of HTS maglev systems, the application laws are concluded. Factors including the critical current density and geometric dimensions of the bulk superconductor, as well as the moving velocity, are discussed. The effects of the multiple back and forth movements are also analyzed. By comparing calculation results of the distributions of the induced current and the levitation force of the bulk superconductor, we can clearly confirm the effect laws of various factors on the electromagnetic characteristics and levitation force. These observations support the physical parameters that are difficult to be tested by experiments. And they also have a significant contribution to the experimental condition selections and optimization of the high-temperature superconducting magnetic levitation.