For the electrodynamic suspension (EDS) system in the high-speed magnetic levitation (Maglev) train, high-temperature superconducting (HTS) coils made of ReBCO-coated conductors can be used as ...levitation magnets. In this paper, a three-dimensional (3-D) model of the HTS EDS system is built for the design of the suspension system of a full-scale high-speed Maglev train. Subsequently, the levitation and drag forces are analyzed using finite-element method (FEM), and the force performances of different operating currents, reaction board thicknesses, and air gap lengths are investigated. And the distribution of the eddy current on the reaction board induced by the moving HTS magnets is obtained. Moreover, according to the eddy current distribution and force analysis results, a mirror image method is proposed to simplify the calculation and accelerate the estimation of the saturated levitation force of an HTS EDS system. The calculation results of the model are verified by the FEM model with an error less than 8%. Finally, the model is expanded to a full-scale HTS EDS system, which validates the feasibility of applying to the high-speed Maglev train.
The high-temperature superconductor (HTS) dc induction heater shows great potential in the efficiency increase and heating quality improvement, which has been validated by previous prototypes. Now, ...Shanghai Jiao Tong University has been developing and fabricating an industrial scale 1-MW HTS dc induction heater in China. The heater is utilized to preheat aluminum billets 446 mm in diameter × 800-1500 mm in length. Two cryocoolers are applied for coil cooling with pluggable sleeve and providing an additional safety margin whose normal operating temperature is 30 K. The magnet consists of a double pancake coils wound by REBa 2 Cu 3 O 7-δ -coated conductors, which are produced by Shanghai Superconductor Technology Company. More than 12-km HTS tapes are used and the inductance of coil with iron is 98 H. The HTS magnet's critical current is 213 A. The 0.5-T dc magnetic field is set up in the two air gaps of HTS magnet with an iron core. The adjustable iron yoke distribution along the axial direction of billets can meet the 100 °C adjustable temperature gradient design requirement. The results will be helpful to design for the commercialization of the HTS dc induction heater.
High-temperature superconducting (HTS) coils could bear larger current density and produce higher magnetic field compared to permanent magnets. An HTS linear synchronous motor (LSM) with its ...secondary excitation system made of HTS coils can provide larger thrust force but unavoidable larger normal force. This paper focuses on the analysis and comparison of different armature structures in an HTS LSM to improve the magnetic flux waveform quality, decrease the normal force, and simultaneously maintain the thrust force. Five alternative armature structures are proposed and investigated, i.e., coreless double layer lap winding (DLLW), yokeless DLLW, coreless and yokeless DLLW, and flat winding with and without iron yoke. Three dimensional models of HTS LSMs are built and verified to compare the magnetic field and force performances of various armature structures using the finite element method. Results indicate that armatures without iron components perform better. Furthermore, the yokeless flat winding is recommended for its 81% reduction of magnetic flux harmonic component and 52% increase of thrust force compared with DLLW.
High-temperature superconducting (HTS) tape stacks could be used in motors as a substitute for permanent magnets (PMs) to improve the power density. However, the magnetization difficulty and safety ...concern limit its wider application. A novel hybrid magnet made of HTS tape stacks and PMs is proposed in this paper and investigated in experimental and numerical modeling methods. A hybrid magnet sample is manufactured and tested using pulsed field magnetization (PFM) at 77.3 K. Then, a 3-D electromagnetic-thermal coupled model is built and verified to simulate the field performance at lower temperatures. After the optimization process of the thickness ratio, an optimal 5-mm hybrid magnet of 0.5-mm tape stack +4.5 mm PM is obtained. Compared with the PM, the optimal hybrid magnet could enhance the magnetic field by 114%. Compared with the pure tape stack of the same size, the hybrid magnet could be magnetized with relatively small pulsed field, could reduce the consumption of the HTS tapes, and could enhance the operation safety especially encountering a cooling system failure. The results offer a novel perspective to introduce the HTS material into the conventional motor applications and provide a possible reference to the future study of HTS motors.
•Influences of Ampere's force applied on each turn of a NI coil are investigated deeply.•Ampere's force influences electrical behavior of a NI coil including its time constant and characteristic ...resistance.•Different components of Ampere's force have different influences on electrical behaviors of a NI coil.•A step-rising energizing method together with a modified circuit model are proposed to calculate instantaneous current-dependent characteristic resistance precisely.
A coil wound with no-insulation (NI) winding technique can present enhanced electrical/thermal stability and more compact structure but poorer energizing/de-energizing instantaneity as compared to an insulated counterpart. The above features of a NI coil are resulted from its turn-to-turn contact resistance, namely, the characteristic resistance Rc. Rc is a rather important parameter of a NI coil, and it is greatly influenced by winding tension, more intrinsically, the compactness of coil winding pack. Alone with the winding tension, Ampere's force that is induced by coil current and magnetic flux density, may also apply on each turn of a NI coil to influence the compactness of coil winding pack, and further the Rc and electrical behaviors of the coil. This paper explores the aforementioned influences caused by Ampere's force through energizing and de-energizing tests. Experimental results show the Rc decreases as charging current increases. Meanwhile, simulation results indicate the Ampere's force applied on each coil turn has a compressive effect and the force is proportional to the square of charging current. Furthermore, a step-rising energizing method together with a modified circuit model are proposed to calculate instantaneous current-dependent Rc. And precise prediction of coil electrical behavior is acquired. Totally, the Ampere's force do have influence on coil electrical behavior especially when the operation current and flux density are large.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In the high-temperature superconducting (HTS) magnets applications, fast quench detection is very important to protect the magnets from burning out. Usually, the method of voltage measurement is ...widely applied to detect quench. However, this method is not satisfied for large HTS magnets intrinsically. Besides, a novel quench detection, which is measured by Raman-scattering-based distributed temperature sensors (DTS) using flexible optical fibers, is suggested to be a potential candidate. To verify the feasibility of this method, we prepared a DTS system based on interrogating Raman-scattering signals and a no-insulation (NI) HTS coil mounted by a 2-m length optical fiber as a test sample. The main results show that critical current of the NI coil is 111 A. In the continued overcurrent-induced quench state under coil current of 160 A, the temperature rise was observed obviously at the position of 1.2 m in the optical fiber, and the temperature was up to 94 K in the near middle region of top surface in the NI coil.
High-temperature superconducting (HTS) coils made of coated conductors that can operate in persistent current mode (PCM) are regarded to be promising in MRI/nuclear magnetic resonance and Maglev ...system. The temporal stability of the magnetic field trapped by the PCM coil is a key issue, which significantly determines the imaging quality of MRI and dynamic behavior of Maglev. This study focuses on the temporal stability of the trapped magnetic field in the double-slit HTS PCM coil, which is magnetized by a field cooling (FC) method at 77 K. The magnetic field decay behavior under different initial fields and FC ramp rates are systematically studied. The experiment results indicate that higher initially trapped field will lead to faster decay, but if the initially trapped field is lower than a certain value, this trend is no longer obvious. The FC ramp rate has a little impact on the field decay. Finally, a numerical model based on R-L circuit and E-J equation is established to fit the decay process. It is found that if the operating current is lower than 60% of the coil critical current, good temporal stability could be achieved. Another long-term experiment is performed that a stability of 8.1 ppm/h is achieved after 19 days' decay.
Closed coils made by second-generation high-temperature superconducting (HTS) coated conductors are promising for superconducting magnets, which operating in a persistent current mode such as MRI, ...NRM, and Maglev. The magnetic field stability for the HTS closed coils after local thermal quench is one of the key indicators to the design of superconducting magnet systems. It significantly affects the operational reliability of superconducting magnets. This paper presents quantitative experiments on the magnetic field stability of a jointless stacked pancake (JSP) coil after local thermal quench. The JSP coil is assembled by stacking double-slit YBCO tapes, which is a true sense of HTS closed coil without any joints. A JSP coil with inner diameter of 30 mm is impregnated by paraffin wax and its central magnetic field stability is measured after various local thermal quench energies. The relationship between quench energy and magnetic field stability time is presented. The magnetic field of the JSP coil will stay stable when quench energy is lower than a threshold value Qm. The magnetic field stability of JSP coils comes from its parallel-structure. Besides, the magnetic field stability of the JSP coil is better than the series-structure closed coil obviously under the same quench energy.
As the capacity of the power grid continues to expand, high-level fault currents might be caused during a contingency, and the problem of short-circuit current over-limitation is imminent. The ...high-temperature superconducting (HTS) fault current limiter (FCL) is an effective method to solve this problem. In this paper, a transient numerical model for the process of limiting current in the inductive FCL is proposed. The model is based on the coupling of multiphysics finite element simulation and a circuit model. The voltage source is used as input, which can simulate the macroscopic characteristics in the process of limiting current, such as the voltage and current waveforms, and can also simulate microscopic characteristics, such as temperature, magnetic field, and electrodynamic force distribution. The short-circuit experimental data of an air core inductive superconducting fault current limiter (SFCL) prototype was compared with the simulation results to verify the reliability of the simulation.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Greenbelt policies are important urban containment policies. On the one hand, they can effectively control the disorderly growth of a city; on the other hand, they can cause other social problems ...because of their strict control over land development. This paper uses data from 2000 and 2010 and the difference-in-differences (DID) method to evaluate the effects of greenbelt deregulation policies on urban land development in the Seoul metropolitan area (SMA) through a quasi-natural experiment. The results show that first, the deregulation of the greenbelt has significantly furthered urban land development that was not caused by economic development or other factors. Second, the greenbelt deregulation had no significant effects on urban land development in the city centers, but has furthered urban land development near the boundary of Seoul City and greenbelt boundaries. Third, in terms of the effects on land development, the greenbelt deregulation has resulted in regional heterogeneity. Specifically, the greenbelt deregulation has had a significant impact on the urban land development in the southern section of the Han River, whereas the effects of the greenbelt deregulation in the northern area of the Han River are not as obvious.
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