• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
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• pp.256-259
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• 2002

The critical currents of sintered $YBa_{2}Cu_{3}O_{6.5+\delta}$ were measured as the variables with the corrosive time in the humid air. The corrosive process was studied by means of the current changes. Ag coating on the textured YBCO and polytetrafluoroethylene (PTFE) coating on the sintered YBCO were prepared. The critical current densities of different YBCO samples with and without coatings were compared. Both Ag coating and PTFE coating can well protect YBCO from moisture and $CO_{2}$.

• Journal of Advanced Research in Ocean Engineering
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• 제2권2호
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• pp.86-98
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• 2016

In this study, after the installation of a subsea pipeline, backfilling was performed in the trenched area. During these operations, a stability problem in the subsea pipeline occurred. The pipeline was directly impacted by environmental loading such as waves and currents that were caused by backfill material when scouring or sediment transport and siltation was carried out. Therefore, this study reviewed whether trenching was necessary, and conducted research into an indigenous seabed property that contains granular soil. A study of cohesive soil was also conducted in order to cross-correlate after calculating the values of the critical Shields parameter relevant to elements of the external environment such as waves and current, and the shear Shields parameter that depends on the actual shearing stress. In case of 1), sedimentation or erosion does not occur. In the case of 2), partial sedimentation or erosion occurs. If the case is 3), full sedimentation or erosion occurs. Therefore, in the cases of 1) or 2), problems in structural subsea pipeline stability will not occur even if partial sedimentation or erosion occurs. This should be reflected particularly in cases with granular and cohesive soil when a reduction in shear strength occurs by cyclic currents and waves. In addition, since backfilling material does not affect the original seabed shear strength, a set-up factor should be considered to use a reduced of the shear strength in the original seabed.

• 한국전기전자재료학회논문지
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• 제21권1호
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• pp.79-84
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• 2008

We are developing a small-sized high temperature superconducting magnetic energy storage (HTS-SMES) magnet with the nominal storage capacity of 600 kJ, which provides electric power with high quality to sensitive electric loads. Critical current and N-value of a high temperature superconductor with large current, which was selected for the development of the 600 kJ HTS-SMES magnet, were investigated in various oblique external magnetic fields. Based on the critical current and N-value measured for the short sample conductor, we discussed the DC V - I characteristic of a model coil fabricated with the same conductor of 500 m. The results show that the measured critical current and N-value of the conductor for parallel field are constant in external magnetic fields less than about 0.2 T. However, for oblique fields, its critical current and N -value abruptly decrease in all external magnetic fields. Moreover, the measured critical current of the model coil well agrees with the numerically calculated one based on the DC V - I characteristic measured for the short sample conductor. This suggest that losses and critical currents for an HTS-SMES magnet made up of a high temperature superconductor with anisotropic characteristic are predictable from the data of a short sample conductor.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.65-68
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• 2004

A lot of R&D efforts are being concentrated on the development of high performance HTS coated conductors(CC). Unlike the HTS Bi-2223 tape, a variety of processes have been tried to fabricate CC tapes. PLD and MOD are believed to be very effective methods, and high critical currents of long length CC tape have been reported. In this study, we prepared two kinds of YBCO CCs to evaluate electromagnetic property. One is YBCO tape deposited on IBAD template by PLD and the other is AMSC's MOD CC tape Critical current (Ic) in magnetic fields, its angular dependency, and n-value were measured and analyzed. Magnetic field property of Ic was appeared to be different due the fabrication process. MOD tape showed higher in-field property, n-value of both PLD and MOD tapes exponentially decreased with magnetic field. MOD tape showed higher n-value in whole magnetic fields.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권1호
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• pp.13-18
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• 1999

To fabricate a 0.7 FJ, 100 kVA $\mu$SMES device for improving power quality in sensitive electric loads, we developed a design code for a $\mu$SMES device and designed the 0.7 MJ $\mu$SMES device by using it. In this study special emphasis was placed in influence of winding tensions on quench currents of superconducting coils because dry superconducting coils are usually quenched by local disturbances due to strand motions. We first investigated the quench currents of a few kA class superconducting cables for various winding tensions experimentally. To prove the validity of the code and develop all techniques related to fabrication and test of the 0.7 MJ $\mu$SMES device, a smaller size superconducting coil was wound with high winding tension of about 15 kgf/$mm^2$ based on the test results of superconducting cables and tested. It isshown form the test results that designed parameters for the smaller size superconducting coil are in good agreements with measured ones and the quench current of the coil with high winding tension reaches nearly to the critical current of the superconducting cable without any training effects.

• 한국자기학회지
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• 제5권3호
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• pp.179-184
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• 1995

{100} 철단결정에 자기장을 가해주거나 혹은 자기장 없이 전류만을 변화 시킬 때의 교류 자기감수율에 관하여 연구 하였다. 작은 자기장과 전류를 철단결정에 걸어줄때, 단결정의 단연적 중앙끈처에는 정사각형 자구가 형성된다. 실험을 통하여 이 자구의 자기화 방향으로 자장을 걸어주변 걸어주는 전류크기와 전류방향의 영향을 받음을 보인다. 이 실험 결과는 전류에의해 중앙에 형성된 자구가 전류의 증감함에따라 변화하는 자구크기로 설명할 수 있다. 실험으로 측정된 자기강수율을 설명하기 위하여 미세 자기이론을 사용하였으며, energy 값을 구히기 위하여 간단한 model을 설정하였다. 이 model로부터 교류 자기감수율을 구할 수 있었으며, 이때 계산한 교류 자기감수율은 한 안정된 구조에서 다른 안정된 구조로 변화하는 전류를 제외한 거의 대부분 전류에 대하여 정량적으로 설명할 수 있었다.

• Journal of Electrical Engineering and Technology
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• 제4권1호
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• pp.98-105
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• 2009

This paper presents the characteristics of soil ionization for different water contents, and the parameters associated with the dynamic properties of a simple model grounding system subject to lightning impulse currents. The laboratory experiments for this study were carried out based on factors affecting the soil resistivities. The soil resistivities are adjusted with water contents in the range from 2 to 8% by weight. A test cell with a spherical electrode buried in the middle of the hemispherical container was used. As a result, the electric field intensity $E_c$ initiating ionization is decreased with the reduction of soil resistivities. Also, as the water content increased, the pre-ionization resistance $R_1$ and the post-ionization resistance $R_2$ became lower with increasing current amplitude. The time-lag to ionization $t_1$ and the time-lag to the second current peak $t_2$ at high applied voltages were significantly shorter than those of low applied voltages. It was found that the soil ionization behaviors are highly dependent on the water content and the applied voltage amplitude.

• 한국초전도ㆍ저온공학회논문지
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• 제22권4호
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• pp.14-19
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• 2020

Here we present the comparative experimental study of the stability of the superconducting state in 4 mm YBCO tapes with copper lamination against local heat disturbances at 77 K. The samples are either directly cooled by immersing a bare YBCO tape into a liquid nitrogen pool or operate in nearly-adiabatic conditions when the tape is covered by a 0.6 mm layer of Kapton insulation. Main quench characteristics, i.e. minimum quench energies (MQEs) and normal zone propagation (NZP) velocities for both samples are measured and compared. Minimum NZP currents are determined by a low ohmic resistor technique eligible for obtaining V - I curves with a negative differential resistance. The region of transport currents satisfying the stationary stability criterion is found for the different cooling conditions. Finally, we use the critical temperature margin as a universal scaling parameter to compare the MQEs obtained in this work for YBCO tapes at 77 K with those taken from literature for low-temperature superconductors in vacuum at 4.2 K, as well as for MgB2 wires cooled with a cryocooler down to 20 K.

• 한국해양학회지
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• 제26권4호
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• pp.332-339
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• 1991

고정밀 탄성파자료, 퇴적물시료, 조류를 분석하여 한국서해안 대조차 지역인 남해 포만에서의 퇴적 양상을 조사하였다. 만에서의 현생퇴적층의 두께는 약 20 m 에 달하 며 불규칙적인 음향기반암을 덮고 있다. 퇴적물은 주로 사질 실트나 실트로 구성되어 있으며, 평균입도는 4-5.5 phi의 범위이고 해안선을 향하면서 세립화하는 경향을 보인 다. 이러한 분포양상은 만에서의 조류의 운동방향과 잘 일치한다. 해저면에서의 조류 의 전단속도는 창조시 0.5-3.3 cm/sec 낙조시 0.7-2.5 cm/sec 의 범위를 보이며, 이러 한 전단속도들의 평균값은 만내에 분포하는 실트입자를 재동하거나 운반할 수 있는 임 계전단속도 값을 능가한다. 이러한 자료들은 조류가 만내에 분포하는 퇴적물 입자들의 이동과 퇴적에 중요한 역할을 하며, 해저면의 표층지형은 주로 조석퇴적작용에 의하여 결정되었음을 시사해 준다.

• Ocean and Polar Research
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• 제36권1호
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• pp.59-69
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• 2014

The long-term mooring performed at a KOGA station, located at about $30^{\circ}20^{\prime}N$, $126^{\circ}12^{\prime}E$ in the East China Sea shelf, shows some different behaviors between "semi-diurnal" and "diurnal currents" defined as the currents with periods around, respectively, a half day and a day. They appear to be predominantly tidal having significant coherences with sea level changes around the semi-diurnal and diurnal frequencies. The "semi-diurnal current" is strongly barotropic all year round. However, contrastingly, it is largely baroclinic in summer in the area about 70 km nearer to the continental slope, referred to as the "slope-area", as was found in previous current observations. The "diurnal current" of tidal origin is strongly barotropic in winter. In spring and summer, however, it becomes more baroclinic although it still remains largely barotropic, also showing more of its barotropic nature than in the "slope-area". The inertial oscillation contributing to the "diurnal current" appears to be more prominent when the current is baroclinic, indicating the important role played by stratification in generation of inertial oscillations. Downward energy propagation of inertial oscillation is not observed, suggesting that it is not created at the surface by wind. Considering that the study area is both near a critical latitude and proximity to the continental slope, it is suggested that parametric subharmonic instability (PSI) plays a significant role in creating the baroclinic inertial oscillation.