• Proceedings of the KSME Conference
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• 2004.04a
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• pp.2070-2075
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• 2004

Performance of a solid oxide fuel cell (SOFC) can be enhanced by converting thermal energy of its high temperature exhaust gas to mechanical power using a micro gas turbine (MGT). A MGT plays also an important role to pressurize and warm up inlet gas streams of the SOFC. In this study, the influence of performance characteristics of the tubular SOFC on the hybrid power system is discussed. For this purpose, detailed heat and mass transfer with reforming and electrochemical reactions in the SOFC are mathematically modeled, and their results are reflected to the performance analysis. The analysis target is 220kWe SOFC/MGT hybrid system based on the tubular SOFC developed by Siemens-Westinghouse. Special attention is paid to the ohmic losses in the tubular SOFC counting not only current flow in radial direction, but also current flow in circumferential direction through the anode and cathode.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.509-512
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• 2006

국내 대형 기력발전단지에서 냉각수로 사용되고 방류되는 해수는 약 150cms로 (100Mwe 당 약 5cms) 약 3,000kW 이상의 수력에너지를 보유하고 있으나, 현재 활용되지 못하고 그대로 해양으로 방류되고 있다. 발전소 방수로는 흐름조건이 비교적 균일하고, 파랑 내습이 없으며 부유사 해조류, 부유물 충돌 등의 문제가 발생하지 않아 자연 해양조건보다 조류력 발전에 매우 유리하나 수심이 낮고, 순환수 계통에의 영향으로 다수의 수차를 설치하기는 어려운 조건을 지니고 있다. 따라서, 인공수로의 균일하고 양호한 흐름조건에 적합한 보다 경제적인 수차를 개발하고, 발전량을 증대하기 위한 수차 배치 기술, 수차 및 발전기 지지구조물의 설계 기술, 계통 연결기술 등을 개발할 필요가 있으며, 이를 위하여 시험용 조류식 발전시스템을 제작하여 수차의 성능 및 전체 발전시스템의 성능을 평가하여 발생되는 문제점을 해결하고자 한다. 본 연구에서는 시험용 조류식 발전시스템을 하동화력발전소 방수로에 적용하기 위하여 현장 특성 분석, 형식 선정, 발전량 산정 등의 시스템 설계를 수행하였다.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.55-61
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• 2008

The Reynolds-Averaged Navier-Stokes(RANS) analysis of the 3-D steady flow around the NREL Phase VI horizontal axis wind turbine(HAWT) rotor was performed. The CFD analysis results were compared with experimental data at several different wind speeds. The present CFD model shows good agreements with the experiments both at low wind speed which formed well-attache flow mostly on the upper surface of the blade, and at high wind speed which blade surface flow completely separated. However, some discrepancy occurs at the relatively high wind speeds where mixed attached and separated flow formed on the suction surface of the blade. It seems that the discrepancy is related to the onset of stall phenomena and consequently separation prediction capability of the current turbulence model. It is also found that strong span-wise flow occurs in stalled area due to the centrifugal force generated by rotation of the turbine rotor and it prevents abrupt reduction of normal force for higher wind speed than the designed value.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.4
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• pp.478-485
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• 2013

This paper focuses on the design and control of a new concept for wind turbines with a planetary gearbox to realize a power split. This concept, where the generated wind power is split into two parts, is to increase the utilization of the wind power and may be particularly suitable for large scale off-shore wind turbines. In order to reduce the cost of the power electronic devices, a synchronous generator, which is driven by the planetary gear, is directly connected to the power grid without electronic converter. A servo drive, which functions as the control actuator, is connected to the power grid by a power electronic converter. With small scale power electronic device, the current harmonics can also be reduced. The speed of the main shaft is controlled to track the optimal tip speed ratio. Meanwhile the speed of the synchronous generator is controlled to stay at the synchronous speed. The minimum rated power of the servo motor and the converter, is studied and discussed in this paper. Different variants of the wind turbine with a planetary gear are also compared. The controller for optimal tip speed ratio and synchronous speed tracking is given.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.3
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• pp.421-424
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• 2016

In order to evaluate the insulation deterioration in the stator windings of air-cooled gas turbine generators(119.2 MVA, 13.8 kV) which has been operating for more than 15 years, diagnostic test and AC dielectric breakdown test were performed on phases A, B and C. Diagnostic test included measurements of AC current, dissipation factor, partial discharge (PD) magnitude and capacitance. ${\Delta}I$ and ${\Delta}tan{\delta}$ in all three phases (A, B, and C) of generator stator windings showed that they were in good condition but PD magnitude indicated marginally serviceable condition. After the diagnostic test, an AC overvoltage test was performed by gradually increasing the voltage applied to the generator stator windings until electrical insulation failure occurred, in order to determine the breakdown voltage. Although phase A of generator stator windings failed at breakdown voltage of 29.0 kV, phases B and C endured the 29.0 kV. The breakdown voltage in all three phases was higher than that expected for good-quality windings (28.6 kV) in a 13.8 kV class generator.

• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.4
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• pp.366-371
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• 2014

The neural network pitch controller using changing rate of generator speed has been suggested in this paper to regulate wind turbine power above the rated wind speed. The changing rate of generator speed is used in the suggested pitch controller as well as the difference between the rated and current generator speed. Matlab/simulink has been used for simulations and it has been shown that the suggested pitch controller regulates generator speed as the rated speed of 122.9[rad/s].

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.4
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• pp.158-162
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• 2017

This paper did basic study on the vertical-axis wind turbine. Namely, This paper was try to find the optimum conditions by using the ANSYS CFX simulation program through the changes of the main-blade angle and sub-blade angle. Main-blade Shape #4 angle $45^{\circ}$ compared to others Shape angle $0^{\circ}$ was increased by 157.2[%] to 263.2[%] in the power output and was increased by 110[%] to 250[%] in the power coefficient. Also, when the Shape #5 Fin length of main-blade doubles, because the power output was 70.8[%] compared to Shape #1 and 27.5[%] compared to Shape #4, and the power coefficient was 60[%] compared to Shape #1 and 28.6[%] compared to Shape #4, the power output and the power efficiency were rather reduced. The output current of Shape #4 was increased 109.9[%] compared to Shape #1 and increased 250[%] compared to Shape #5, and The output voltage of Shape #4 was increased 22.5[%] compared to Shape #1 and increased 3.7[%] compared to Shape #4.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.8
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• pp.1172-1180
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• 2017

This study analyzed competition in peak load plants between CCGT and GT instead of competition between base and peak load plants like in previous studies. In common overseas power markets, CCGT and GT claim certain market shares as peak load plants with the latter boasting a high utilization rate as reserve plants. In South Korea, however, there has been no introduction of GT in the market that opened in 2001 with no analysis cases of GT's economy as a peak load plant. The current power market of South Korea is run on the cost-based pool, which allows for no price spikes. Since the capacity payment criteria for compensations for missing money are set based on GT generators, the power market uses GT generators as marginal plants. The purposes of this study were to analyze the competitive edge of GT generators as peak load plants in the domestic power market of South Korea and identify the causes of GT's failure in market entry, thus assessing the adequacy of market signals in the domestic power market.

• Wind and Structures
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• v.23 no.4
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• pp.301-311
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• 2016

The numerous benefits of Savonius turbine such as simple in structure, has appropriate self-start ability, relatively low operating velocity, water acceptance from any direction and low environmental impact have generated interests among researchers. However, it suffers from a lower efficiency compared to other types of water turbine. To improve its performance, parameters such flow pattern, pressure and velocity in different conditions must be analyzed. For this purpose, a detailed description on the flow field of various types of Savonius rotors is required. This article presents a numerical study on a nonlinear two-dimensional flow over a classic Savonius type rotor and a Benesh type rotor. In this experiment, sliding mesh was used for solving the motion of the bucket. The unsteady Reynolds averaged Navier-Stokes equations were solved for velocity and pressure coupling by using the SIMPLE (Semi-Implicit Method for Pressure linked Equations) algorithm. Other than that, the turbulence model using $k-{\varepsilon}$ standard obtained good results. This simulation demonstrated the method of the flow field characteristics, the behavior of velocity vectors and pressure distribution contours in and around the areas of the bucket.

• Wind and Structures
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• v.18 no.3
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• pp.253-265
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• 2014

The platform and floating structure of spar type offshore wind turbine systems should be designed in order for the 6-DOF motions to be minimized, considering diverse loading environments such as the ocean wave, wind, and current conditions. The objective of this study is to optimally design the platform and substructure of a 3MW spar type wind turbine system with the maximum postural stability in 6-DOF motions as well as the minimum material cost. Therefore, design variables of the platform and substructure were first determined and then optimized by a hydrodynamic analysis. For the hydrodynamic analysis, the body weight of the system was considered, and the ocean wave conditions were quantified to the wave forces using the Morison's equation. Moreover, the minimal number of computation analysis models was generated by the Design of Experiments (DOE), and the design variables of the platform and substructure were finally optimized by using a genetic algorithm with a neural network approximation.