gye-won Hong - Academia.edu (original) (raw)

Papers by gye-won Hong

Progress in Superconductivity, 2005

Physica C-superconductivity and Its Applications, Sep 1, 2008

We fabricated BSCCO-2212 (2212) rods using a casting process and evaluated the effects of anneali... more We fabricated BSCCO-2212 (2212) rods using a casting process and evaluated the effects of annealing time and size to improve critical current (I c). Diameters of rods were 1.0 cm and 1.6 cm and annealing was performed from 60 h to 200 h at 800°C. The I c of rods increased with increasing annealing time, probably due to increased grain size of 2212. Annealing time of the highest I c for the smaller rod was shorter (150 h) than that of the larger rod (200 h). This size effect seems to be related to different grain sizes of the intermediate phases such as 2201 and secondary phases in the ingot. In addition, we successively fabricated 2212 tubes from the rod by making a hole in the center region which contained inhomogeneous microstructures. This method was simple and I c did not significantly decrease. However, critical current density (J c) improved when as much as 60% of the diameter in the center region was machined out of the rod.

Progress in Superconductivity and Cryogenics, 2009

High temperature superconductor (HTS) coated conductors has high hysteretic magnetization loss wh... more High temperature superconductor (HTS) coated conductors has high hysteretic magnetization loss which is an obstacle for the AC applications of coated conductors. We propose a method to reduce the magnetization loss of the coated conductor. It is the mechanical striation method by load variety using office knife. The magnetization loss measured in the mechanical striated YBCO coated conductor without copper layer was compared with the loss generated by perpendicularly exposed external magnetic filed. The reduction in magnetization loss due to the mechanical striation is clearly shown at higher field and was dependent on the striation number. The mechanical striation method was proven to have additional advantages of a low cost and high fabrication process.

Progress in Superconductivity and Cryogenics, 2010

Silver stabilizing layer of coated conductor has been prepared by dip coating method using organi... more Silver stabilizing layer of coated conductor has been prepared by dip coating method using organic silver complexes containing 10 wt% silver as a starting material. Coated silver complex layer was dried in situ with hot air and converted to crystalline silver by post heat treatment in flowing oxygen atmosphere. A dense continuous silver layer with good surface coverage and proper thickness of 230 nm is obtained by multiple dip coatings and heat treatments. The film heat treated at showed good mechanical adhesion and crystallographic property. The interface resistivity between superconducting YBCO layer and silver layer prepared by dip coating was measured as . Additional protecting copper layer with the thickness of was successfully deposited by electroplating. The critical current measured with the specimen prepared by dip coating and sputtering on same quality YBCO layer showed similar value of ~140 A and proved its ability to replace sputtering method for industrial production of coated conductor.

Korean Journal of Materials Research, 1994

Progress in Superconductivity, 2006

Progress in Superconductivity, 2006

Progress in Superconductivity, 2007

IEEE Transactions on Applied Superconductivity, Jun 1, 2020

This paper extends a conventional adaptive fuzzy sliding mode controller with integer order to fr... more This paper extends a conventional adaptive fuzzy sliding mode controller with integer order to fractional ones for a three-phase active power filter (APF) in order to track instruction current quickly and precisely and offset the harmonic current in the electrical grid. A fractional sliding surface is utilized to make the system work on the designed sliding surface stably. A fuzzy system with fractional adaptive laws is employed to precisely approximate the unknown parameters in the APF system. Simulations are given to demonstrate the excellent performance of the proposed controller. Moreover, the superiority of the proposed controller over the conventional adaptive fuzzy sliding mode controller is also illustrated by showing the smaller total harmonic distortion, which is a significant index to evaluate the current quality in the smart grid. INDEX TERMS Sliding mode control, fuzzy system, fractional adaptive control.

Progress in Superconductivity and Cryogenics, 2009

Mechanical and electrical properties of silver stabilizer layer of coated conductor, which as pre... more Mechanical and electrical properties of silver stabilizer layer of coated conductor, which as prepared with nano silver paste as starting materials, have been investigated, Nano silver paste was coated on a YBCO film by dip coating process at a diping speed of 20m/min. Coated film was dried in air and heat treated at in an oxygen atmosphere. Adhesion strength between YBCO and silver layer was measured by a tape est(ASTM D 3359). Hardness and electrical conductivity of the samples were measured by pencil hardness test (ASTM D 3363) and volume resistance test by LORESTA-GP (MITSHUBISHD, respectively. The sample heat-treated at showed poor adhesion 1B, but samples heat treated at higher than showed enhanced adhesion of 5B. The silver layer heat-treated at showed the high hardness value larger than 9 H, low volume resistance, surface resistance value as well as superior current carrying capacity compared to sputtered silver. SEM observations showed that a dense silver layer was formed with a thickness of about . Dip coated silver layer prepared by using nano silver paste showed superior electrical and mechanical characteristics.

Progress in Superconductivity and Cryogenics, 2003

In a HTS transformer, the perpendicular component of magnetic flux density () applied to HTS tape... more In a HTS transformer, the perpendicular component of magnetic flux density () applied to HTS tapes of pancake windings becomes larger than that of solenoid winding, thereby decreasing the critical current in the HTS tapes. This paper introduces several methods to reduce applied to the HTS tapes in the transformer with double pancake windings by changing winding arrangements and the relative permeability of flux diverters. We have conducted a winding design for a single-phase 1MVA 22.9kV/6.6kV HTS transformer. We observed a change of due to a variation of gap-length between the high voltage windings and the low voltage windings, reciprocal arrangement and an increase of the number of the high voltage pancake. We also observed a change of Br on the HTS tapes due to variation of the relative permeability of flux diverters placed between the high voltage winding and the low voltage winding. Finally, we have designed a 1MVA 22.9kV/6.6kV HTS transformer winding using suggested methods and calculated transformer parameters by the 3D finite element method.

한국자기학회 학술연구발표회 논문개요집, Dec 1, 2010

한국자기학회 학술연구발표회 논문개요집, Dec 1, 2010

Korean Journal of Materials Research, 1998

Physica C-superconductivity and Its Applications, Oct 1, 2006

ABSTRACT We fabricated 2212-SrSO4 composites by the melt casting process and evaluated the effect... more ABSTRACT We fabricated 2212-SrSO4 composites by the melt casting process and evaluated the effect of melt flowing on the critical current (Ic) by using two different pouring methods, i.e., the conventional vertical casting and the tilt casting methods. It was observed that the 2212-SrSO4 rod processed by the tilt casting method had a higher Ic value than that processed by the vertical casting method. This improved Ic is considered to be related to the more homogenous microstructure due to the laminar flow of the melt. In addition, we evaluated the variation of the Ic with the SrSO4 content. The Ic value was found to be significantly dependent on the SrSO4 content: the Ic of the 2212 increased as the SrSO4 content increased and reached a peak value (260A at 77K) at an SrSO4 content of 6wt.%, and then decreased when the SrSO4 content was further increased. This increase is probably due to the lower porosity, larger grain size and stronger texture, resulting from the enhanced diffusion kinetics. The possible causes of the variation in the Ic with the SrSO4 content based on the microstructural observations were discussed in detail.

Progress in Superconductivity, 2005

Physica C-superconductivity and Its Applications, Sep 1, 2008

We fabricated BSCCO-2212 (2212) rods using a casting process and evaluated the effects of anneali... more We fabricated BSCCO-2212 (2212) rods using a casting process and evaluated the effects of annealing time and size to improve critical current (I c). Diameters of rods were 1.0 cm and 1.6 cm and annealing was performed from 60 h to 200 h at 800°C. The I c of rods increased with increasing annealing time, probably due to increased grain size of 2212. Annealing time of the highest I c for the smaller rod was shorter (150 h) than that of the larger rod (200 h). This size effect seems to be related to different grain sizes of the intermediate phases such as 2201 and secondary phases in the ingot. In addition, we successively fabricated 2212 tubes from the rod by making a hole in the center region which contained inhomogeneous microstructures. This method was simple and I c did not significantly decrease. However, critical current density (J c) improved when as much as 60% of the diameter in the center region was machined out of the rod.

Progress in Superconductivity and Cryogenics, 2009

High temperature superconductor (HTS) coated conductors has high hysteretic magnetization loss wh... more High temperature superconductor (HTS) coated conductors has high hysteretic magnetization loss which is an obstacle for the AC applications of coated conductors. We propose a method to reduce the magnetization loss of the coated conductor. It is the mechanical striation method by load variety using office knife. The magnetization loss measured in the mechanical striated YBCO coated conductor without copper layer was compared with the loss generated by perpendicularly exposed external magnetic filed. The reduction in magnetization loss due to the mechanical striation is clearly shown at higher field and was dependent on the striation number. The mechanical striation method was proven to have additional advantages of a low cost and high fabrication process.

Progress in Superconductivity and Cryogenics, 2010

Silver stabilizing layer of coated conductor has been prepared by dip coating method using organi... more Silver stabilizing layer of coated conductor has been prepared by dip coating method using organic silver complexes containing 10 wt% silver as a starting material. Coated silver complex layer was dried in situ with hot air and converted to crystalline silver by post heat treatment in flowing oxygen atmosphere. A dense continuous silver layer with good surface coverage and proper thickness of 230 nm is obtained by multiple dip coatings and heat treatments. The film heat treated at showed good mechanical adhesion and crystallographic property. The interface resistivity between superconducting YBCO layer and silver layer prepared by dip coating was measured as . Additional protecting copper layer with the thickness of was successfully deposited by electroplating. The critical current measured with the specimen prepared by dip coating and sputtering on same quality YBCO layer showed similar value of ~140 A and proved its ability to replace sputtering method for industrial production of coated conductor.

Korean Journal of Materials Research, 1994

Progress in Superconductivity, 2006

Progress in Superconductivity, 2006

Progress in Superconductivity, 2007

IEEE Transactions on Applied Superconductivity, Jun 1, 2020

This paper extends a conventional adaptive fuzzy sliding mode controller with integer order to fr... more This paper extends a conventional adaptive fuzzy sliding mode controller with integer order to fractional ones for a three-phase active power filter (APF) in order to track instruction current quickly and precisely and offset the harmonic current in the electrical grid. A fractional sliding surface is utilized to make the system work on the designed sliding surface stably. A fuzzy system with fractional adaptive laws is employed to precisely approximate the unknown parameters in the APF system. Simulations are given to demonstrate the excellent performance of the proposed controller. Moreover, the superiority of the proposed controller over the conventional adaptive fuzzy sliding mode controller is also illustrated by showing the smaller total harmonic distortion, which is a significant index to evaluate the current quality in the smart grid. INDEX TERMS Sliding mode control, fuzzy system, fractional adaptive control.

Progress in Superconductivity and Cryogenics, 2009

Mechanical and electrical properties of silver stabilizer layer of coated conductor, which as pre... more Mechanical and electrical properties of silver stabilizer layer of coated conductor, which as prepared with nano silver paste as starting materials, have been investigated, Nano silver paste was coated on a YBCO film by dip coating process at a diping speed of 20m/min. Coated film was dried in air and heat treated at in an oxygen atmosphere. Adhesion strength between YBCO and silver layer was measured by a tape est(ASTM D 3359). Hardness and electrical conductivity of the samples were measured by pencil hardness test (ASTM D 3363) and volume resistance test by LORESTA-GP (MITSHUBISHD, respectively. The sample heat-treated at showed poor adhesion 1B, but samples heat treated at higher than showed enhanced adhesion of 5B. The silver layer heat-treated at showed the high hardness value larger than 9 H, low volume resistance, surface resistance value as well as superior current carrying capacity compared to sputtered silver. SEM observations showed that a dense silver layer was formed with a thickness of about . Dip coated silver layer prepared by using nano silver paste showed superior electrical and mechanical characteristics.

Progress in Superconductivity and Cryogenics, 2003

In a HTS transformer, the perpendicular component of magnetic flux density () applied to HTS tape... more In a HTS transformer, the perpendicular component of magnetic flux density () applied to HTS tapes of pancake windings becomes larger than that of solenoid winding, thereby decreasing the critical current in the HTS tapes. This paper introduces several methods to reduce applied to the HTS tapes in the transformer with double pancake windings by changing winding arrangements and the relative permeability of flux diverters. We have conducted a winding design for a single-phase 1MVA 22.9kV/6.6kV HTS transformer. We observed a change of due to a variation of gap-length between the high voltage windings and the low voltage windings, reciprocal arrangement and an increase of the number of the high voltage pancake. We also observed a change of Br on the HTS tapes due to variation of the relative permeability of flux diverters placed between the high voltage winding and the low voltage winding. Finally, we have designed a 1MVA 22.9kV/6.6kV HTS transformer winding using suggested methods and calculated transformer parameters by the 3D finite element method.

한국자기학회 학술연구발표회 논문개요집, Dec 1, 2010

한국자기학회 학술연구발표회 논문개요집, Dec 1, 2010

Korean Journal of Materials Research, 1998

Physica C-superconductivity and Its Applications, Oct 1, 2006

ABSTRACT We fabricated 2212-SrSO4 composites by the melt casting process and evaluated the effect... more ABSTRACT We fabricated 2212-SrSO4 composites by the melt casting process and evaluated the effect of melt flowing on the critical current (Ic) by using two different pouring methods, i.e., the conventional vertical casting and the tilt casting methods. It was observed that the 2212-SrSO4 rod processed by the tilt casting method had a higher Ic value than that processed by the vertical casting method. This improved Ic is considered to be related to the more homogenous microstructure due to the laminar flow of the melt. In addition, we evaluated the variation of the Ic with the SrSO4 content. The Ic value was found to be significantly dependent on the SrSO4 content: the Ic of the 2212 increased as the SrSO4 content increased and reached a peak value (260A at 77K) at an SrSO4 content of 6wt.%, and then decreased when the SrSO4 content was further increased. This increase is probably due to the lower porosity, larger grain size and stronger texture, resulting from the enhanced diffusion kinetics. The possible causes of the variation in the Ic with the SrSO4 content based on the microstructural observations were discussed in detail.