Myung-Hwan Sohn

Joint resistances between two parallel high Tc superconducting tapes

Eight different types of joining between two parallel high Tc superconducting (HTS) tapes were prepared and current-voltage (I-V) characteristic curves were investigated at 77 K, liquid nitrogen temperature. Contact resistances of joint parts with 25 mm in length were estimated from I-V curves. Lowest contact resistance among eight samples having different types of joining was 0.497 /spl mu//spl Omega/. The best joining method is to do crossly joining with HTS tapes on two parallel HTS tapes after filling solder paste into their gap. In this case, lowest joint resistance was 0.15 /spl mu//spl Omega/ at 77 K and 0.05 /spl mu//spl Omega/ at 28 K. Joule heat of a joint sample generated at 30 K and at 100 A was calculated 0.492 mW. Also, in I-V curve of samples crossly joined with HTS tapes, it was found that joint resistance does not depend on variation of magnetic fields (0/spl sim/7000 G) at 77 K. From consideration of Joule heat generation, such joining method is available for fabricating the field winding of superconducting rotating machine.

Development of a 100 hp synchronous motor with HTS field coils

A 3-phase, 100 hp, 4 pole, 1800 rpm superconducting synchronous motor built and tested in Korea Electrotechnology Research Institute(KERI). This machine consists of HTS rotor and air-core stator. The HTS field windings are composed of the double-pancake coils wound with AMSCs stainless steel-reinforced Bi-2223 tape conductor. These were assembled on the support structure and fixed by a bandage of glass-fiber composite. The cooling system is based on the heat transfer mechanism of the thermosyphon by using GM cryocooler as cooling source. The cold head is in contact with the condenser of a Ne-filled thermosyphon. The rotor assembly was tested independently at the stationary state and combined with stator. The open circuit, no-load, and short circuit characteristic were obtained. Also, load tests in motor mode driven by inverter and generator mode connected to resister load bank were conducted. This paper will present design, construction, and experimental test results of the 100 hp HTS machine.

High temperature superconducting synchronous motor

This paper deals with high temperature superconducting (HTS) synchronous motor, which has two characteristics: the HTS magnet with iron plates as field coil, and the solid nitrogen (SN/sub 2/) as a cryogen. The HTS magnet has iron plates to achieve the maximum current-carrying capacity and the simple shape that can easily be wound and jointed. The HTS magnet with iron plates, magnet optimized current distribution, and initial magnet are presented through FEA (finite element analysis), manufacturing and testing these magnets. SN/sub 2/ is employed for keeping the operating temperature of HTS synchronous motor. To make the SN/sub 2/ of liquid nitrogen (LN/sub 2/), liquid helium (LHe) passes into the heat exchanger and cools its own temperature. Two types of heat exchangers are designed and manufactured to make the SN/sub 2/, and each of the temperature characteristics is compared.

Performance Analysis of a Toroid-Type HTS SMES Adopted for Frequency Stabilization

Superconducting magnetic energy storage (SMES) can overcome fluctuations in frequency because of its fast response time in charging and discharging energy. To stabilize the fluctuations in frequency of wind power generation systems (WPGSs), HTS SMES systems should be connected to the terminal of the WPGSs. Ulleung Islands power network in Korea was modeled with a real-time digital simulator (RTDS) to demonstrate the effectiveness of SMES at stabilizing frequency. A toroid-type HTS SMES cooled by conduction cooling and a DC/DC chopper to charge and discharge current were fabricated for the experiment. The simulation results show the frequency stabilization effected by the HTS SMES system with its operational characteristics such as real time variation in current and temperature.

Optimal Design of Superconducting Motor to Improve Power Density Using 3D EMCN and Response Surface Methodology

This paper proposes an effective design process for 1 MW HTS superconducting motor by using 3-dimensional equivalent magnetic circuit network method (3D EMCN) and response surface methodology (RSM). During the process, 3D EMCN is used with a simplified 3D analysis model to get electric parameters in short time. RSM is used for the motor optimal design to improve power density. The usefulness of this method is verified through the comparison of the performances of the optimal geometry and those of the initial geometry

Design and electrical characteristics analysis of 100 HP HTS synchronous motor in 21st Century Frontier Project, Korea

A 100 hp class superconducting motor in the 21st Century Frontier R&D Program of Korea has been designed. A theoretical model of high temperature superconducting (HTS) motor was presented by two-dimensional electromagnetic field analysis. The motor is composed of HTS field winding, cold damper shield, air-gap armature winding and laminated machine shield. The HTS field winding consists of racetrack type double pancake coils wound with Bi-2223 HTS tapes operated at about 30 K. The operating current of the HTS tape conductor could be determined by the magnetic field distribution calculated in the HTS field winding and the I/sub c/ - B characteristics of a practical HTS conductor, taking account of its anisotropy.

Microstructures in high-Jc Tl-1223/Ag tapes

Abstract High- T c Tl-1223/Ag tapes with a nominal composition of (Tl 0.93 Bi 0.22 )(Sr 1.6 Ba 0.4 )Ca 2 Cu 3 O x were prepared using the powder-in-tube method combined with the two step reaction method. Their microstructures were examined using scanning and transmission electron microscopy. Tape A ( J c = 5 500 A/cm 2 at 77 K under 0 T) prepared using rolling only has a lower J c than tape B ( J c = 14 000 A/cm 2 ) prepared using pressing. In both tapes Tl-1223 forms plate-like grains. Although the size of the plates in tape A is larger than those in tape B, their mutual connection is poorer. Many subgrains are formed in each grain with small angle boundaries, which are composed of tilt-type as well as twist-type components in most cases. The boundaries might be considered as effective pinning sites for magnetic flux as far as the tilt component predominates. Additionally, small holes were found at the subgrain boundaries.

Purification of the Coolant for Hot Roller by Superconducting Magnetic Separation

It is important to recycle industrial wastewater in the aspect of energy saving and minimizing the environment damage. Steel manufacture factories make an effort to purify and recycle wastewater from the manufacturing processes. A steel manufactory in Korea, POSCO (POhang iron and Steel COmpany) has also concerned about the treatment of wastewater for long time. The coolant of hot roller at steel making factory includes suspended solid (SS) like steel fines, iron oxide and emulsified oil. A laboratory-scale conduction cooled high temperature superconducting (HTS) magnet was used for high gradient magnetic separation (HGMS) systems. It consists of eight double-pancake sub-coils, two HTS current leads, a GM cryo-cooler and a cryostat without a radiation shield vessel. Sub coils were wound with 1 G HTS tapes of Sumitomo Electric Industries by wet-winding method. A Cryo-cooled high temperature superconducting magnet system with 70 mm room temperature bore and 250 mm of height was prepared. This magnet was used for batch type HGMS system. Superconducting HGMS system that had a purpose to purify the wastewater was assembled. Various magnetic seeding reactions were investigated to increase the reactivity of coagulation.

Purification of Wastewater From Paper Factory by Superconducting Magnetic Separation

It is environmentally important to recycle the wastewater, since paper factories use a large amount of water and equivalent amount of wastewater is generated. Conventional water treatment facilities like precipitation process need large-scale equipment and wide space to purify the wastewater of paper factory. In case of massive waste water, high gradient magnetic separation (HGMS) parts are more effective to purify it rapidly and to occupy relatively small space, since large voids at filter with HGMS are adopted. In this respect, we prepared two types of superconducting magnets in order to apply HGMS parts for wastewater purification process. We made cryo-cooled Bi-2223 (HTS) superconducting magnet parts with room temperature bore in diameter of 70 mm and 200 mm in height. Also, cryo-cooled Nb-Ti superconducting magnet with room temperature bore in diameter of 100 mm and 600 mm in height was used for magnetic separator. Magnetic filters were designed by the analysis of magnetic field distribution at superconducting magnets. The faster wastewaters flow rate was, the worse the degree of clarity in treated water was. The ability of wastewater treatment in the case of magnetic separation used with 10 of magnetite particles was better than that in the case of 5 of magnetite particles.

Fabrication and Characteristics of 2G HTS Current Leads

2nd generation high temperature superconducting (2G-HTS) tape consists of multi-layers such substrate, buffer layer, superconducting layer and reinforced lamination tapes. 2G HTS tape is a candidate of good materials for current lead of superconducting magnet system owing to its low thermal conductivity. However, joint resistance between 2G HTS tapes and terminal block can be a major problem because of high electrical resistivity of substrate, buffer layer and reinforced lamination tapes of 2G HTS. So specially considering joint resistance between 2G tapes and terminal block, 2G HTS current lead for 400 A was designed and fabricated. This current lead was consisting of two terminal blocks, a support bar or tube, protection tube and six 2G HTS tapes. Its total length was 300 mm and body diameter 18.3 mm. At liquid nitrogen temperature (77 K) critical current (Ic) of this HTS current lead was 600 A, about 1.5 times the operating current 400 A. Conductive heat loss of 2G HTS current lead between 60 K and 7 K was 50 mW.