• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.1
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• pp.42-46
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• 2003

Arresters are deteriorated by overvoltages or impulse currents, and the resistive leakage current of arresters increases as the deterioration of the arrester progresses, showing an increase in the 3$^{rd}$ harmonic component of the leakage current. In this reason, arrester diagnostic techniques based on the 3$^{rd}$ harmonic leakage current as a reference parameter of deterioration are widely used. The technique, however, includes an error due to the harmonics of power system voltage. Therefore, the influence of the harmonics on arrester diagnostics should be considered. In this paper, we designed a PSpice ZnO arrester model to simulate the influence of the voltage harmonics described above. A pure sinusoidal voltage and its the 3r harmonic voltage were applied to the model, and the leakage current components were analyzed. From the simulation results, it is confirmed that the peak value of resistive leakage current depends not only on the phase of the 3$^{rd}$ harmonic voltage but also on the magnitude of it. Consequently, the errors caused 1)y the harmonic voltage could be minimized by correcting the magnitude of leakage current upon analyzing the harmonics.cs.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.1
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• pp.23-29
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• 2005

This paper presents the characteristics of leakage currents flowing through ZinC Oxide(ZnO) surge arrester blocks under mixed direct and 60 Hz alternating voltages. A mixed voltage, in which an alternating voltage is superimposed upon a direct voltage, appears on the HVDC system network. The mixed direct and alternating voltage generator with a peak open-circuit of 10 kV was designed and fabricated. The leakage currents and V-I curves for the fine and used ZnO surge arrester blocks were measured as a function of the voltage ratio k, where the voltage ratio k is defined as the ratio of the peak of alternating voltage to the peak of the mixed voltages. The resistive component in the leakage current in the low conduction region is significantly increased with increasing the voltage ratio k. The V-I characteristic curves for the mixed voltages lies between the direct and alternating characteristics, and the cross-over phenomenon in the high conduction region was appeared.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.348-351
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• 1999

We investigated current limiting properties for an SFCL of YBCO thin film coated with an Au layer. The YBCO film of 1 mm wide and 400 nm thick could carry the current 9.6 A$_{peak}$ without quench. The SFCL limited the fault current below 7.6 A$_{peak}$, which otherwise increases above 65 A$_{peak}$ and melted down at the potential fault current of about 100 A$_{peak}$ which is 10 times greater than the quench current. This means that the Au layer successfully protected the superconducting film by dispersing the heat generated at hot spots and electrically shunting the YBCO film.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.11
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• pp.493-497
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• 2005

This paper dealt with the influence of harmonic voltages on arrester diagnostics and its compensation method by using a designed Pspice arrester model. A pure sinusoidal voltage and its 3$^{rd}$ harmonic voltage were applied to the model, and the leakage current components were analyzed. The simulation results have shown that the peak value of resistive leakage current depends not only on the phase of the 3$^{rd}$ harmonic voltage but also on the magnitude of it. In this paper, an approximated 5$^{th}$ order polynomial formula by the Least-Square-Technique was derived, and correction factors which compensate the error caused by the 3$^{rd}$ harmonic voltage were calculated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.497-500
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• 1999

This paper reports on the fabrication and characteristics of recessed gate GaN MESFETs fabricated using a photoelectrochemical wet etching method. The unique etching process utilizes photo-resistive mask and KOH based etchant. GaN MESFETs with successfully recessed gate structure was characterized in terms of dc and RF performance. The fabricated GaN MESFET exhibits a current saturation at $V_{DS}$ = 4 V and a pinch-off at $V_{GS}$ =-3V The peak drain current of the device is about 230mA/mm at 300 K and the value is remained almost same for 500K operation. The $f_{T}$ and $f_{max}$ from the device are 6.357Hz and 10.25 GHz, respectively.y.y.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.338-341
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• 2006

This paper presents the leakage current characteristics of ZnO varistors exposed to the $8/20{\mu}s$ lightning impulse currents as functions of the number of injection and amplitude of impulse currents. The surge simulator system ECAT that can generate $8/20{\mu}s$ impulse currents with a peak short-circuit of $5[kA_p]$ was used. Leakage currents flowing through ZnO varistors subjected to the $8/20{\mu}s$ impulse currents were measured under 60 Hz AC voltages. The trend curves of resistive leakage current of ZnO varistors were analytically calculated.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.170-173
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• 2006

[ $CuInS_2$ ] filims were appeared from 0.84 to 1.27 of Cu/In composition ratio and sulfur composition ratios of $CuInS_2$ thin films fabricated, Also when Cu/In composition ratio was 1.03, $CuInS_2$ thin film with chalcopyrite structure had the highest XRD peak (112). And lattice constant (a) of and grain size of the film tin s ambient were appeared a little larger than those in only Vacuum The films in S ambient were p-type with resistive of around $10^{-1}{\Omega}cm$ and optical energy band gaps of the films in S ambient were appeared a little larger than those in only Vacuum. Analysis of the optical energy band gap of $CuInS_2$ thin films a value of 1.53eV.

• Progress in Superconductivity and Cryogenics
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• v.6 no.3
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• pp.50-55
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• 2004

We fabricated and tested a resistive type superconducting fault current limiter (SFCL) of three-phase 6.6 $kV_{rms}/200 A_{rms}$ rating based on YBCO thin films grown on sapphire substrates with a diameter of 4 inches, Short circuit tests were carried out at a accredited test facility for single line-to- ground faults, phase-to-phase faults and three-phase faults, Each phase of the SFCL was composed of 8${\times}$6 elements connected in series and parallel respectively. Each element was designed to have the rated voltage of 600 $V_{rms}$. A NiCr shunt resistor of 23 Ω was connected to each element for simultaneous quenches. Firstly, single phase-to-ground fault tests were carried out. The SFCL successfully developed the impedance in the circuit within 0.12 msec after fault and controlled the fault current of 10 $kA_{rms} below 816 A_{peak}$ at the first half cycle. In addition, in case of phase-to-phase fault and three- phase fault test. simultaneous quenches among the SFCLs of the phases successfully accomplished. In conclusion. the SFCL showed excellent performance of current limitation upon fault and stable operation regardless of the amplitude of fault currents.

• Progress in Superconductivity and Cryogenics
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• v.13 no.1
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• pp.31-35
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• 2011

A Hybrid Fault Current Limiter(FCL) which has more advantages in fast response and thermal characteristics than a simple resistive FCL had been proposed by our group. The Hybrid FCL consists of a resistive FCL for the magnitude of the first peak of fault current, and a fast switch for detecting fault current and generating the repulsive force within a cycle in fault situation. In ideal case, the impedance of the fast switch wound with two other kinds of HTS tape is negligibly zero in normal operation. But, during the fault situation, each HTS tape has different quench characteristics because of asymmetric current distribution. And this phenomenon causes effective flux and this flux opens the switch through the repulsive force applied to a metal plate of the fast switch. The magnitude of the repulsive force affects the switching characteristics of the fast switch. It should be large enough to raise the metal plate up. Otherwise the arc re-out break which are caused by not enough repulsive force to raise the metal plate up can cause unintended operation of the fast switch. In this paper, the numerical calculation of the repulsive force applied to the metal plate of the fast switch in various combinations of HTS tapes was performed by using the short-circuit test and finite element method.

• The Journal of Korean Physical Therapy
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• v.21 no.3
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• pp.25-32
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• 2009

Purpose: This study examined whether breathing exercises might increase the chest expansion and pulmonary function of stroke patients. Methods: Twenty four patients with stroke were assigned randomly into two groups: a combination of diaphragmatic resistive breathing and pursed-lip breathing exercise (CB) group (n=10) and control group (n=14). The CB group completed a 4-week program of diaphragmatic resistive breathing and pursed-lip breathing exercise. The subjects were assessed using the pre-test and post-test measurements of the chest expansion (length for resting, deep inspiration, deep expiration, deep expiration-inspiration) and pulmonary function (forced vital capacity (FVC), forced expiratory volume at one second (FEV1), FEV1/FVC, peak expiratory flow (PEF), vital capacity (VC), tidal volume (TV), expiratory reserve volume (ERV), inspiratory reserve volume (IRV)). Results: A comparison of the chest expansion between the pre and post tests revealed similar rest, deep inspiration, deep expiration, and deep expiration-inspiration lengths in the CB and control groups (p>0.05). A comparison of the pulmonary function between pre and post tests, revealed significant improvements in the FVC, FEV, PEF, VC, IRV, and ERV in the CB group (p<0.05). There was a significant difference in the FVC, FEV1, PEF, VC and IRV between the 2 groups (p<0.05). Conclusion: These findings suggest that breathing exercise should help improve the pulmonary function, such as the volume and capacity. This suggests that the pulmonary functions of stroke patients might be improved further by a continued respiratory exercise program.