• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.4
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• pp.715-722
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• 1998

A large electric system of a vacuum circuit breaker(VCB) has been studied for the electro-thermal analysis by finite element methods. Since the heat generation in VCB causes not only energy loss but deterioration of the VCB system with oxidization of parts, the overheating of the system must be prevented. For the analysis, a finite element formulation is derived for both electric analysis and thermal analysis that are coupled together. Two sets of formulations are uncoupled after finite dimensional approximation. First, the electric potential is obtained for the entire field and scaled to the given electric current. The electric field obtained is then used to calculate the heat generation in the VCB system including contacts and connections for the calculation of the temperature distribution in the entire domain. The finite element analysis is carried out to study the effect of shapes and locations of contacts and connections. From the results, the existing VCB has been modified to enhance its capacity with reduction of heat generation and temperature elevation.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.357-360
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• 2009

The present study focused on the segmented cell which has the similar performance to unaltered (not segmented) cell in real operating condition. Many literatures have been made the segmented cell to observe the behavior of local current density distribution in the single cell. However, it has been lack of scheme to segment the cell in that the detailed interpretation of segmenting in analytic point of view was insufficient. Hence, the basic idea of segmenting was introduced to determine the component to be segmented in anode side of unit cell. The electrical contact/bulk resistance was measured by using four wire/probe method through each part of cell components including MEA, GDL, Bipolar Plate and Current Collector. Electron transport mechanism was predicted by comparing resistance values which were obtained from the experiment. As a result, this offered a great benefit to segment the cell efficiently. With this method further experiments would be conducted in research areas which require current density distribution at the same operating condition as unaltered cell.

• Transactions of the Society of Information Storage Systems
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• v.10 no.2
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• pp.32-38
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• 2014

Heat emission from the laser diode used in the optical disc drive and the defects from the increased temperature at the system have attracted attentions from the field of the information storage device. Thermoelectric refrigerator is one of the fine solutions to solve these thermal problems. The refrigeration performance of thermoelectric device is dependent on the thermoelectric material's figure-of-merit. Meanwhile, high electrical contact resistivity between metal electrode and p- and n-type thermoelectric materials in the device would lead increased total electrical resistance resulting in the degeneracy in performance. This paper represents the manufacturing process of the PbTe-based material which has one of the highest figure-of-merit at medium-high-temperature, ~ 600K to 900 K, and the nickel contact layer for reduced electrical contact resistance at once, and the results showing the decent contact structure and figure-of-merit even after the long-term operation environment.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.8
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• pp.438-444
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• 2000

We report the effects of etch process parameters on the ohmic contact formation in the plasma etching of GaN. Planar inductively coupled plasma system with $CH_4/H_2/Ar$gas chemistry has been used as etch reactor. The contact resistance and the specific contact resistance have been investigated using transfer length method as a function of RF bias power and %Ar gas concentration in total flow rate. AES(Auger electron spectroscopy) analysis revealed that the etched GaN has nonstoichiometric Ga rich surface and was contaminated by carbon and oxygen. Especially large amount of carbon was detected at the sample etched for high bias power (or voltage) condition, where severe degradation of contact resistance was occurred. We achieved the low ohmic contact of $2.4{\times}10^{-3} {\Omega}cm^2$ specific contact resistance at the input power 400 W, RF bias power 150 W, and working pressure 10mTorr with 10 sccm $CH_4$, 15 sccm H2, 5 sccm Ar gas composition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.64-64
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• 2008

연속공정이 가능한 Roll to Roll sputter system을 이용하여 플렉시블 indium tin oxide(ITO) 투명전극을 PET(polyethlyene terephthalate) 기판위에 성막하였다. 연속 성막공정을 위해 Roll to Roll sputter system에서의 unwinder roller와 rewinder roller를 이용한 servomotor의 rolling으로 기판의 움직임이 완벽히 제어되었으며, 외부 응력으로 부터의 안정성 및 성막 공정 시의 PET 기판의 열적 변형을 최소화하기 위한 접촉식 냉각방식의 cooling system을 main drum으로 사용하였다. 또한 고분자 기판과 투명전극 사이의 adhesion을 향상시키기 위한 전처리 공정으로 gridless linear ion beam source를 pretreatment system으로 구축하였다. 이렇게 제작된 Roll to Roll sputter system을 이용하여 PET 기판위에 연속공정을 통해 ITO 투명전극을 성막하였다. 성막된 플렉시블 ITO/PET 투명전극은 XRD, HREM, SEM 분석을 통하여 main drum의 cooling에 의해 완전한 비정질 구조를 나타내었음을 확인할 수 있었으며, 비록 Roll to Roll sputter system을 통하여 상온에서 성막 되었음에도 불구하고 최적화 된 조건에서 가시광선 영역 83.46 %의 높은 광투과도 값과 47.4 Ohm/square의 비교적 낮은 먼저항 값을 얻을 수 있었다. 또한 Bending test 결과를 통하여 ion source의 전처리 공정으로 굽힘/평의 반복적 응력에 따른 전기적 특성 열화를 최소화 할 수 있음을 보였다. 최적화된 플렉시블 투명전극을 이용하여 P3HT:PCBM 기반의 플렉시블 유기태양전지를 제작하였으며, 제작된 유기태양전지로부터 1.88%의 power conversion efficiency (PCE)을 확보함으로써 플렉시블 유기태양전지 제작을 위한 ITO/PET 투명전극 성막 공법으로써 Roll to Roll sputter system의 적용가능성을 확인할 수 있었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.10
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• pp.788-795
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• 2013

A magnesium bipolar plate whose surface was protected by thinly deposited silver layer was investigated as an alternative to existing graphite bipolar plate of PEM fuel cells. Thin silver layer of $3{\mu}m$ was deposited on a magnesium alloy substrate by physical vapor deposition (PVD) method in an environment of $180^{\circ}C$. A number of tests were conducted on the fabricated magnesium based bipolar plates to determine their suitability for use in PEM fuel cell stacks. The test on corrosion resistance in the same pH condition as in a PEM operation demonstrated the layer protected the magnesium alloy substrate, while unprotected substrate suffered from severe corrosion. The contact resistance of the fabricated bipolar plate was less than $20m{\Omega}-cm^2$ which was superior to the conventional bipolar plates. A single cell was constructed using the fabricated bipolar plates and power output was measured. Due to the enhanced conductivity caused by low contact resistance, slight increase was observed in current density and output voltage. With low density of the magnesium substrate and ease on machining, the weight reduction of the stack of 30~40 % is possible to produce the same power output.

• Journal of the Society of Disaster Information
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• v.14 no.2
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• pp.130-140
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• 2018

Purpose: In this paper, we propose a design technique for the safety characterization grounding in the construction of the photovoltaic power generation complex which can be useful and useful as an alternative power energy source in our society. In other words, we will introduce the application of safety grounding for each application, which can improve and optimize the reliability of the internal grid from the cell module to the electric room in the photovoltaic power generation complex. Method: We analyze the earth resistivity of the soil in the solar power plant and use the computer program (CDEGS) to analyze the contact voltage and stratospheric voltage causing the electric shock, and propose the calculation and calculation method of the safety ground. In addition, we will discuss the importance of semi-permanent ground electrode selection in consideration of soil environment. Results: We could obtain the maximum and minimum value of ground resistivity for each of the three areas of the data measured by the Wenner 4 - electrode method. The measured data was substituted into the basic equation and calculated with a MATLAB computer program. That is, it can be determined that the thickness of the minimum resistance value is the most favorable soil environment for installing the ground electrode. Conclusion: Through this study, we propose a grounding system design method that can suppress the potential rise on the ground surface in the inner grid of solar power plant according to each case. However, the development of smart devices capable of accumulating big data and a monitoring system capable of real-time monitoring of seismic changes in earth resistances and grounding systems should be further studied.

• Polymer(Korea)
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• v.32 no.4
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• pp.340-346
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• 2008

The aim of this study is to understand the effect of structure on the dispersion of both CNT and GNF in the phase of synthesized polyurethanes matrix. Various CNT/PU and GNF/PU composite films were prepared. Polyurethane having a different hard segment was blended with both CNT and GNF. PU having HDI as hard segment showed good dispersion with both CNT and GNF because of their linear structural character and molecular kinesis while PU having aromatic ring showed poor dispersion with those due to their structural complexity. Structural effect also induced the increase of its electro conductivity. The PU/CNT composite showed a bad dispersion (because of phase separation between PU matrix and CNT) but good electro conductivity at its surface (because CNT was collected on the surface of composite film due to low density of CNT). PU/CNT and PU/GNF composite films have quite low normalized sheet resistance value compared with silver/PU nanocomposite film because the fiber type filler could have much more contact points than that of sphere shaped silver particles have.

• Applied Chemistry for Engineering
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• v.21 no.3
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• pp.265-271
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• 2010

Desalination effects of capacitive deionization (CDI) process was studied using $TiO_2$/activated carbon electrode. In order to enhance the wettability of electrode and decrease a electrode resistance, $TiO_2$ was coated on activated carbon. By means of $TiO_2$ coating on activated carbon, electric double layer to adsorption content in CDI process was increased. It was identified from TEM, XRD, and XPS that the activated carbon based on $TiO_2$ composite was fabricated successfully by means of sol-gel method. As a results of cyclic voltammetry and impedance, it was identified that $TiO_2$/activated carbon electrode has more electric double later capacitance and less diffusion resistance than activated carbon. Also charge-discharge and ion conductivity profiles showed that the ion removal ratios of $TiO_2$/activated carbon electrode in NaCl electrolyte of $1000\;{\mu}S/cm$ more increased about 39% than that of activated carbon. In conclusion it was possible to identify that the carbon electrode coated $TiO_2$ as electrode material was more effective than raw carbon electrode.

• Proceedings of the KIEE Conference
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• 2001.11a
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• pp.112-114
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• 2001

In this letter, we report on the investigation of Si/Ti, Pt/Si/Ti, Co/Si/Ti Ohmic contacts to p-type 4H-SiC. The contacts were formed by a 2-step vacuum annealing at $550^{\circ}C$ for 5 min, $850^{\circ}C$ for 2 min respectively. The contact resistances were measured using the transmission line model method, which resulted in specific $10^{-4}{\Omega}cm^2$, and the physical properties of the contactcontact resistivities in the $9.2{\times}10^{-4}$, $7.1{\times}10^{-4}$ and $4.5{\times}s$ were examined using microscopy, AES(auger electron spectroscopy). AES analysis has shown that, at this anneal temperature, there was a intermixing of the Ti and Si, migration of into SiC. Overlayer of Pt, Co had the effect of decreasing the specific contact resistivity and improving the surface morphology of the annealed contact.