• 풍력에너지저널
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• 제14권4호
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• pp.50-56
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• 2023

With the abnormal weather phenomena caused by global warming, the frequency and intensity of lightning strikes are increasing, and lightning accidents are becoming one of the biggest causes of failures and accidents in offshore wind turbines. In order to secure generator operation reliability, effective and practical measures are needed to reduce lightning damage. Because offshore wind turbines are tall structures installed at sea, the possibility of direct lightning strikes is very high compared to other structures, and the role of surge protection devices to minimize damage to the electrical and electronic circuits inside the wind turbine is very important. In this study, a varistor, which is a key element for a class 1 surge protection device for direct lightning protection, was developed. The current density was improved by changing the varistor composition, and the distance between the electrode located on the varistor surface and the edge of the varistor was optimized through a simulation program to improve the fabrication process. Considering the combined effects of heat distribution, electric field distribution, and current density on the optimized varistor surface, silver electrodes were formed with a gap of 0.5 mm. The varistor developed in this study was confirmed to have an energy tolerance of 10/350 ㎲, 50kA, which is a representative direct lightning current waveform, and good protection characteristics with a limiting voltage of 2 kV or less.

• 대한환경공학회지
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• 제34권10호
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• pp.671-677
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• 2012

본 연구는 에멀젼 연료의 특성과 배출가스에 대하여 연구하였다. 엔진 배출가스 측정은 엔진 dinamometer로 실시하였다. 실험분석 결과 emulsion 연료의 참발열량과 총발열량은 이론적 계산과 실제측정결과 오차범위인 ${\pm}0.5%$로 산정된다. 점도와 밀도는 물의 첨가량이 증가할수록 증가하였다. 또한 emulsion 연료는 보관온도가 높아질수록 상분리가 빠르게 진행된다. $20^{\circ}C$의 경우가 가장 안정된 상태를 오래 유지하며, 그 다음은 $50^{\circ}C$가, 가장 불안정한 상태를 보이는 것은 $80^{\circ}C$인 것을 알 수 있었다. 연소실험 결과 emulsion 연료가 Bunker-A 보다 낮은 NOx, Smoke 수치를 보였으며, 총 NOx는 1,000 rpm 41%, 1,200 rpm 10%, 1,500 rpm 32% 2,500 rpm 28%, 총 smoke는 1,000 rpm 42%, 1,200 rpm 65%, 1,500 rpm 70%. 2,000 rpm 62%. 2,500 rpm 82%의 저감이 가능하였다.

• Journal of Radiation Protection and Research
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• 제38권4호
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• pp.228-233
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• 2013

세계적으로 원전의 가동 년수 증가로 인하여 증기발생기와 같은 중요 설비의 교체가 지속적으로 이루어지고 있으며, 해체 시에는 대량의 방사성 금속 폐기물이 일시에 발생한다. 이러한 방사성 폐기물을 규제해제 후에 재활용하기 위해서는 정확한 잔류방사능을 측정하여야 한다. 그러나, 원자력시설에서 발생되는 금속 폐기물은 형상이 복잡하고, 재질별 특성이 다양하기 때문에 잔류방사능을 정확히 측정하기가 어렵다. 본 연구에서는 방사성 금속 폐기물의 정확한 잔류방사능을 측정하기 위한 절차를 수립하였고, 오염 대상 선원항 평가, 시료 대표성 확보 방안, 대면적 오염도 측정 장치 제작 및 밀도에 의한 자체흡수 보정인자 등을 평가하였다. 특히, 복잡한 구조의 금속 폐기물에 대하여 시료의 대표성을 확보하기 위하여 용융시킨 후 단순한 형태의 시료를 제조하였으며, 금속의 밀도 차이에 따른 보정인자를 결정하여 방사능 측정 결과의 신뢰성을 향상시켰다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.318-318
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• 2012

A graphene layer is most important materials in resent year to enhance the electrical properties of semiconductor device due to high mobility, flexibility, strong mechanical resistance and transparency[1,2]. The resistance switching memory with the graphene layer have been reported for next generation nonvolatile memory device[3,4]. Also, the graphene layer is able to improve the electrical properties of memory device because of the high mobility and current density. In this study, the resistance switching memory device with metal-oxide nano-particles embedded in polyimide layer on the graphene mono-layer were fabricated. At first, the graphene layer was deposited $SiO_2$/Si substrate by using chemical vapor deposition. Then, a biphenyl-tetracarboxylic dianhydride-phenylene diamine poly-amic-acid was spin coated on the deposited metal layer on the graphene mono-layer. Then the samples were cured at $400^{\circ}C$ for 1 hour in $N_2$ atmosphere after drying at $135^{\circ}C$ for 30 min through rapid thermal annealing. The deposition of aluminum layer with thickness of 200 nm was done by a thermal evaporator. The electrical properties of device were measured at room temperature using an HP4156a precision semiconductor parameter analyzer and an Agilent 81101A pulse generator. We will discuss the switching mechanism of memory device with metal-oxide nano-particles on the graphene mono-layer.

• KIEAE Journal
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• 제15권1호
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• pp.155-160
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• 2015

The annual average of energy sources is continuously increasing at a rate of 5.8%, and particularly, the power generation proportion of new/renewable energy is increasing significantly. Furthermore, South Korea has established a national energy master plan for 2008-2030 and is aiming at obtaining approximately 11% of total energy production from the wind turbine sector. Although offshore wind turbines are similar to wind turbines installed on land, they require materials with excellent dynamic properties and durability to prevent damage due to seawater at the lower parts and connecting parts. The lower parts of wind turbines are submerged in seawater, and the upper and lower parts are connected by filling the connecting part with grout. This paper describes the test results of the process of determining the mix ratios to develop ultra-high grout for offshore wind turbines. There is virtually no relevant technology regarding grout for offshore wind turbines in South Korea that can be referenced for the process of determining the mix ratios. Therefore, tests were conducted for determining compression strength, elastic modulus, flexural strength, density, constructability (floor test), and early strength by referencing a high-performance grout produced in South Korea, and the mixing process for achieving the goal strengths was described using the Korean Industrial Standards (KS) as the reference.

• 전기학회논문지P
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• 제55권1호
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• pp.13-20
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• 2006

In this paper, a control method of ozone generator for a tiny deodorizer is proposed, and also a cooling technique is described which is cooling down the flowing air gap into a silent discharger to $2[^{\circ}C]$ to generate ozone of high density and diffusing power. As the digital control system for this method, a double feedback loop is designed which detects the voltage and current of equivalent capacitor of the discharger and compensates for the poor power waveform caused by the noise at high discharging frequency. During the plant modeling of this system, computing time factor is considered as a unique parameter of the power system to improve the respond characteristics with regard to fluctuating load and to replenish the computing time delay of the controller. Through the experiment, sinusoidal input current for discharger can be acquired and all the effectiveness of this accurate control system over unstable ozone discharger are proved.

• 조명전기설비학회논문지
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• 제13권3호
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• pp.40-47
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• 1999

본 연구에서는 개발하고자 하는 저에너지 대면적 전자빔 발생장치는 원리로서 발생원인 글로우 발전에 의한 플라즈마로부터 이온을 음극으로 가속, 충돌하게 하여 그때 발생하는 2차전자를 전자빔원으로 하여 전자를 가속·제어하는데 바탕을 두고 있으며, 본 연구에서는 이러한 원리를 기본으로 이론적 해석을 통한 고효율의 저에너지 대면적 전자빔 발생장치개발의 설계 및 제작에 대해서 연구하였으며, 또한 빔 에너지의 안전성과 방전조건을 고려한 최적의 방전 파라메타를 설정하여 대면적의 균일한 빔 인출을 가능케 하였다.

• Journal of Electrical Engineering and Technology
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• 제10권2호
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• pp.545-550
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• 2015

High Temperature Superconducting (HTS) synchronous generators can be designed with either an air-core type or iron-core type. The air-core type has higher efficiency under rated rotating speed and load than the iron-core type because of the iron losses which may produce much heat. However, the total length of HTS wire in the air-core type is longer than the iron-core type because the generated magnetic flux density of the air-core type is low. This paper deals with designs of 10 MW air-core and iron-core HTS wind power generators for wind turbines. Fully air-core, partially iron-core, and fully iron-core HTS generators are designed, and various stator winding methods in the three HTS generators are also considered, such as short-pitch concentrated winding, full-pitch concentrated winding, short-pitch distributed winding, and full-pitch distributed winding. These HTS generators are analyzed using a 3D finite elements method program. The analysis results of the HTS generators are discussed in detail, and the results will be effectively utilized for large-scale wind power generation systems.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.336-340
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• 2009

This paper presents experimental results carried out on the purge characteristic of the anodic dead-end mode fuelcell and how to improve the cell performance by pulsation effects. The dead-end mode fuelcell has some merits that a fuel supplying device is not needed and the cell power is higher than that in the open mode fuelcell. However, the purge is necessary for preventing the porous media from being flooded by liquid water formed in the channel. At this time, the un-reacted fuel is discharged with the liquid water together in purge process. The discharged fuel can make the fuel efficiency lower. Therefore, the number of purge times should be decreased for the better fuel efficiency. In this study, the outlet of the anode channel was equipped with a purge solenoid valve and a pulsation generator. The purge times was decreased when the current density decreased and operation pressure increased without the pulsation effects. In addition, when the pulsation effects such as various frequencies or amplitudes were applied, purge times was alleviated up to 40%.

• 동의생리병리학회지
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• 제27권2호
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• pp.189-195
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• 2013

This study was designed to analyze the effects of methanol extracts and solvent fractions of the young branch of Prunus persica on scavenging activity of ROS, RNS and inhibiting activity of oxidative modification in human LDL induced by copper ion or free radical generator. The scavenging capacities of the fractions on DPPH radical, superoxide radical, nitric oxide and peroxynitrite were exhibited the highest in ethylacetate fraction, followed by butanol fraction. In the copper-induced LDL oxidative modification system, the highest antioxidant activity was revealed in ethylacetate fraction, and butanol fraction exhibited a similar activity. However, solvent fractions of the young branch of Prunus persica showed a relatively low antioxidant activity in the AAPH-mediated LDL oxidation. In addition, ethylacetate and butanol fractions also inhibited the copper-mediated LDL oxidation in the REM assay, which was comparable to that of the positive controls, including EDTA, ascorbic acid and BHT. Futhermore, a content of total phenolics in these two fractions was higher than that of the other fractions. These results indicated that ethylacetate and butanol fractions of the young branch of Prunus persica were useful for the prevention of the free radical- or metal ion-induced oxidative damages.