Fei Yen

Superconducting Excitation System of a Small Scale Linear Synchronous Motor

A four pole superconducting excitation system that was part of a linear synchronous motor (LSM) system, was fabricated and its thrust and normal forces studied experimentally. Four cases were investigated, air-cored, with a ferromagnetic (FM) back plate, an FM core, and with both an FM back plate and core. With a total of only 15 m of YBCO coated conductor in the form of four coils as the excitation system, thrust output of up to 95 N while operating at 77 K with a magnetic gap of 10 mm was obtained in one particular case. The results of the studied superconducting LSM system help better understand the feasibility of their applications to drive systems for Maglev trains.

Performance of a Small-Scale High Temperature Superconducting Linear Synchronous Motor Prototype

Four coils made of YBCO-coated conductor wire were fabricated and connected in series to make up the excitation system of a linear synchronous motor system with a stator made of ordinary copper wire. The electromagnetic forces experienced by the superconducting coils with respect to the stator were studied in the static case. We began with the study of one single coil, followed by two coils connected in series, and finally, four coils in series from which the largest force obtained was of 53.9 N at a gap of 10 mm at 77 K. The critical current, n-value, and inductance were also measured for the coils so that the power dissipation of the field windings can be calculated. This paper also helps us understand whether linear motors with superconducting components are currently economically feasible with present commercially available superconducting wire.

Normal Force Analysis on a High Temperature Superconducting Linear Synchronous Motor

The normal forces of a single sided high temperature superconducting linear synchronous motor (SLSM) have been investigated at 77 K. The SLSM consisted of a superconducting coil made of YBCO coated conductor as the excitation system and a conventional three phase copper wound armature as the stator with a gap of 10 mm in between. Alternating current up to 7.5 A at 10.5 Hz was applied to the armature and direct current up to 40 A to the excitation system. Studies were also made on addition of iron components such as a core and a back plate to the excitation system. The force components adding up to the resulting normal force are discussed. With minimal normal forces compared to the large thrust forces generated, the advantages of such SLSM system for maglev applications are discussed.

Hydrostatic Pressure Effects on the Critical Current of YBCO Coated Conductor Wire

The critical current density of optimally doped bulk YBCO superconductor has been found to increase with the application of external hydrostatic pressure. This paper reports the transport measurements of the critical current (Ic) of YBCO in the form of a coated conductor (CC) wire under hydrostatic pressure up to 0.24 GPa at 77 K. No noticeable change was observed in both the Ic and n-value of the CC sample in the studied pressure range. Two possible scenarios are discussed to explain the observed effect.

Experimental Study of the Electromagnetic Forces of a HTS Bulk Magnet Subjected to Sinusoidal Traveling Magnetic Field

High temperature superconducting (HTS) bulk sample acts as quasi-permanent magnet when it traps magnetic field, and the superconducting bulk magnet can substitute the traditional permanent magnet in the engineering of the linear motor for the purpose of achieving higher efficiency. The electromagnetic forces between the HTS bulk magnets and the ac magnetic field are the most important parameters to consider for the engineering of a motor. We measured the static vertical and thrust forces of an HTS magnet subject to a sinusoidal traveling magnetic field at different trapped fields and at different current amplitude and frequencies. The force relaxation of the HTS bulk magnet was also compared with that of a traditional permanent magnet. The feasibility of replacing the conventional magnet in the ac application machines by HTS bulk ones was preliminary validated experimentally.

Recent Developments of the High Temperature Superconducting Maglev at ASCLab

This year marks the tenth anniversary of the first man-loading high temperature superconducting (HTS) maglev test vehicle “Century” in the world. This report summarizes development advances of major topics related to the HTS maglev vehicle at the Applied Superconductivity Laboratory (ASCLab) at Southwest Jiaotong University (SWJTU). The HTS Maglev measurement systems are described, including the HTS maglev dynamic test system capable of speeds up to 300 km/h. Through these measurement systems, many problems related to the HTS maglev have been studied such as system optimization, stability control, influence from ramp angles, influence from AC field, and investigation of the systems properties at temperatures lower than 77 K. Apart from experimental studies, the 3-D model of the HTS maglev was constructed via two different methods to simulate the Maglevs behavior.

Levitation Force Transition of High-Tc Superconducting Bulks Within a Maglev Vehicle System Under Different Dynamic Operation

In the practical application of a High-Tc Superconducting (HTS) maglev vehicle, the onboard HTS bulks are inevitably exposed to a varying inhomogeneous magnetic field due to limited magnetic field precision during the processing and assembling of the permanent magnetic guideway (PMG). To explore the levitation force of YBa2Cu3O7-x bulk samples with respect to a PMG in such changing external magnetic fields, we study experimentally the wave detail and general transition of the levitation force at different dynamic operation modes with the aid of a spinning circular PMG. The rotation of the circular PMG simulates translational movement of the superconductor with respect to a PMG and the rotational speed was set under several shift processes for simulating the different running operation speeds of HTS maglev vehicle. The highest linear equivalent experimental speed was 238 km/h. The change in levitation force was almost instantaneous in accordance to the varying of the vertical component of the applied field, and generally attenuated with running time. The saturation behavior after a change in speed was discussed thoroughly. This observed phenomenon is of great importance in the design and application of the HTS maglev system.

Induced Currents in Close-Ended Type-II Superconducting Coils

The electrical properties of a close-ended coil made of REBCO-coated conductor wire are studied via the measurement of its induced currents upon exposure to a sinusoidal magnetic field at different frequency. Results show a similarity to the behavior of currents inside an RLC circuit where the peak amplitude is dependent on the contact resistance of the solder joining the two ends of the coil and the resonant frequency, i.e., a function of the inductance of the coil and penetration rate of fluxons into the superconducting layers. Our findings suggest highly feasible applications stemming from such experimental setup in the field of linear and rotating machinery and low-frequency high-quality-factor resonators.

Hydrostatic Pressure Effect on the Critical Current Density of First-Generation Bi-2223 Superconducting Wire

A method to transport up to 180 A of current into the sample space of a pressure cell without causing thermal instabilities at 77 K was developed in order to study the critical current Ic of samples of first-generation Bi-2223 superconducting wire at different hydrostatic pressures. Ic was found to linearly decrease with increasing application of external pressure and was found to be irreversible upon release of pressure. The n-value of the voltage-current curves at different pressure was also found to systematically decrease. The decrease in Ic and the irreversibility effect is attributed to the deformation of the filamentary walls of the wire.

Magnetization Method Design of Bulk Multi-Seeded High Temperature Superconductors

The potential application of bulk high temperature superconductor (HTS) magnets has attracted much attention because of the potential high trapped flux in HTS magnets. This paper focuses on the magnetization method design of bulk multi-seeded HTS magnets for obtaining their better flux-trapping performance. Firstly, three different magnetization methods were carried out based on the current experimental setup to find a better way of magnetizing a bulk melt-texture three-seeded YBaCuO superconductor. The experimental results indicated that when the three domains of this three-seeded YBaCuO bulk were magnetized in order, the maximum trapped flux was higher than that when only one domain was magnetized. However, this method costs about three times of the magnetization time than the other two methods and the increasing ratio was only about 11.11%. It has been found that another method of magnetizing only the middle domain could also get a good result such as the uniformity of trapped flux is good. In order to improve the current experimental magnetization conditions for further improvement, two sheets of iron were designed to attach two poles of the electromagnet (Lakeshore, Model EM4-CV) for increasing the magnetizing area, and that all domains of a bulk multi-seeded HTS can be magnetized in one time. Firstly, the appropriate size and thickness of the iron sheets was simulated and optimized by Comsol Multiphysics. It has been found that the magnetic field between two poles was highest when the thickness of iron was 2 mm and the length was 68 mm. Then, the simulating and optimization results had been verified by the following experiments. According to the comparison experiments, it is proved that to choose the magnetization method that only magnetizing the middle domain with the improved setup is helpful to obtain larger and more homogeneous magnetic flux for the bulk multi-seeded HTS magnet due to the added iron sheets.