• Journal of Power Electronics
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• 제13권2호
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• pp.186-196
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• 2013

This paper presents a low voltage-stress AC-linked charge equalizing system for balancing the energy in a serially connected, valve-regulated lead acid battery string using a modular converter that consists of multiple transformers coupled together. Each converter was coupled through an AC-linked bus to increase the overall energy transfer efficiency of the system and to eliminate the problem of the unbalanced charging of batteries. Previous solutions are based on centralized and modularized topologies. A centralized topology requires a redesign of the hardware and related components. It also faces a high voltage stress when the number of batteries is expanded. Modularized solutions use low-voltage-stress, double-stage, DC-linked topologies which leads to poor energy transfer efficiency. The proposed solution uses a low-voltage stress, AC-linked, modularized topology that makes adding more batteries easier. It also has a better energy transfer efficiency. To ensure that the charge equalization system operates smoothly and safely charges batteries, a small intelligent microcontroller was used in the control section. The efficiency of this charge equalization system is 85%, which is 21% better than other low-voltage-stress DC-linked charging techniques. The validity of this approach was confirmed by experimental results.

• Corrosion Science and Technology
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• 제12권5호
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• pp.227-232
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• 2013

A number of components installed in the secondary system of nuclear power plants are exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), Cavitation, Flashing, and LDIE (Liquid Droplet Impingement Erosion). Those aging mechanisms can lead to thinning of the components. In April 2013, one (1) inch small bore piping branched from the main steam line experienced leakage resulting from wall thinning in a 1,000 MWe Korean PWR nuclear power plant. During the normal operation, extracted steam from the main steam line goes to condenser through the small bore piping. The leak occurred in the downstream of an orifice. A control valve with vertical flow path was placed on in front of the orifice. This paper deals with UT (Ultrasonic Test) thickness data, SEM images, and numerical simulation results in order to analyze the extent of damage and the cause of leakage in the small bore piping. As a result, it is concluded that the main cause of the small bore pipe wall thinning is liquid droplet impingement erosion. Moreover, it is observed that the leak occurred at the reattachment point of the vortex flow in the downstream side of the orifice.

• 한국유체기계학회 논문집
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• 제7권5호
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• pp.29-35
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• 2004

The turbine efficiency is an important factor in power plant, and accurate evaluation of steam turbine performance is the key issue in turbo machinery industry. The difficulty of evaluating the steam turbine performance due to its high steam temperature and pressure environment makes the most steam turbine tests to be replaced by air similarity test. This paper presents how to decide the similarity conditions of the steam turbine test and describes its limitations and assumptions. The test facility was developed and arranged to conduct an air similarity turbine performance test with various inlet pressure, temperature and mass flow rate. The eddy-current type dynamometer measures the turbine-generated shaft power and controls the rotating speed. Pressure ratio of turbine can be controled by back pressure control valve. To verify its test results, uncertainty analysis was performed and relative uncertainty of turbine efficiency was obtained.

• 한국산학기술학회논문지
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• 제20권2호
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• pp.1-6
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• 2019

본 연구의 목적은 100kW급 연료전지 시스템의 열관리 성능을 실도로 운전조건에서 분석하여, 성능 해석 모델링을 개발하는 것이다. 개발된 모델을 적용하여, 열관리 시스템의 운전조건 변화에 따른 성능 변화를 고찰하고자 한다. 해석 모델링은 핵심부품들에 대한 성능 평가 데이터를 바탕으로, 성능에 영향을 주는 변수들로 개발하였다. 개발된 연료전지 열관리 시스템 해석 모델링으로 다양한 실차 운전조건에서의 최적 열관리 시스템에 대한 전력소비량을 분석하였다. 주요하게, 연료전지 열관리시스템 핵심부품(워터펌프, 냉각 팬, 3 Way Valve, 라디에이터)에 대한 성능 특성 분석 후 모델링을 진행하였다. 개발된 모델링으로 운전조건에 따른 유량 예측을 하였고, 실험값과 예측값과의 비교분석을 통하여서, 해석 모델링에 대한 검증을 진행하였다. 과도해석을 통하여서, 냉시동시 냉각수 온도가 특정온도까지의 소요시간을 예측하였다. 스택 운전조건에서 스택 입출구 온도가 적정 수준에서 움직이기 위한 열관리 시스템 운전조건에 대한 예측을 진행하였다. 그 결과를 바탕으로, 소모전력과 열방출량과의 비교분석을 하였다. 개발된 해석 모델링은 핵심부품들의 성능 변화시 연료전지 시스템 운전에 대한 영향도를 분석할 수 있도록 활용할 예정이다.

• 한국지열·수열에너지학회논문집
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• 제5권1호
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• pp.1-6
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• 2009

In this study, an ORC (Organic Rankine Cycle) is investigated for a low-temperature geothermal power generation by a simulation method. A steady-state simulation model is developed to analyze cycle's performance. The model contains a turbine, a pump, an expansion valve and heat exchangers. The turbine and pump are modelled by an isentropic efficiency. Simulations were carried out for the given heat source and sink inlet temperatures, and given flow rate that is based on the typical power plant thermal-capacitance-rate ratio. HFC-245fa is considered as a working fluid of the cycle. Simulation results, at the given secondary working fluids conditions, show that even though the power can be presented by both the evaporating temperature and the turbine inlet superheat, it depends on the evaporating temperature primarily.

• 에너지공학
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• 제24권2호
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• pp.40-44
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• 2015

중수로 일차냉각재계통 액체방출밸브의 개방압력에 대한 안전여유 및 시간지연을 반영하여 열수력코드로 경년열화가 반영된 노심에 대해 민감도를 평가하였다. 과거에는 안전해석을 수행할 때 안전여유와 시간지연을 반영하여 평가하지 않았으나, 월성1호기 안전해석 인허가 심사과정중 반영 평가하였다. 중수로 안전해석에서 압력경계는 일차냉각재계통 액체방출밸브이다. 따라서 액체방출밸브 응동이 안전해석에 직접적인 영향을 주므로 안전여유와 시간지연 부가가 안전해석 결과에 미치는 영향을 파악하고 해석에 반영하기 위해 일차냉각재계통 과압이 걸리는 사고들에 대해 평가하였다.

• 열처리공학회지
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• 제35권3호
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• pp.121-129
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• 2022

Recently the growth of the renewable energy production has caused the flexible operation in LNG combined cycle power plant. Due to the rapid start and stop operations, large CrMoV castings used for turbine casings and valve bodies could be distorted and lead to replacement or welding repair. This study was performed to find out the characteristics of the repair welding for a damaged CrMoV casting steel. A typical field repair method (arc & TIG welding) was applied to making specimens. The degraded N2 packing head sample from the steam turbine was used. The evaluations of weldments were carried out in terms of microstructural characterization, microhardness measurements, tensile, creep-rupture and fatigue tests. Color etching was also applied for better understanding of welding microstructures. As the boundary between HAZ and base material was deteriorated by welding, it caused microstructural changes formed during PWHT and the shortening of the remaining residual life. By comparing the properties according to repair welding method, it was possible to derive what important welding factors were. As a result, arc welding method is more suitable for repair welding on CrMoV castings.

• 한국유체기계학회 논문집
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• 제17권6호
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• pp.104-108
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• 2014

The recent Fukushima nuclear power plant accidents shows that the core make up at high RCS pressure condition is very important to prevent core melting. The core make up flow at high pressure condition should be driven by gravity force or passive forces because the AC-powered safety features are not available during a Station Black Out (SBO) accident. The reactor Coolant System (RCS) mass inventory is continuously decreased by releasing steam through the pressurizer safety valves after reactor trip during a SBO accident. The core will be melted down within 2~3 hours without core make up action by active or passive mode. In the new design concept of a Hybrid Safety Injection Tank (Hybrid SIT) both for low and high RCS pressure conditions, the low pressure nitrogen gas serves as a charging pressure for a LBLOCA injection mode, while the PZR high pressure steam provides an equalizing pressure for a high pressure injection mode such as a SBO accident. After the pressure equalizing process by battery driven initiation valve at a high pressure SBO condition, the Hybrid SIT injection water will be passively injected into the reactor downcomer by gravity head. The SBO simulation by MARS code show that the core makeup injection flow through the Hybrid SIT continued up to the SIT empty condition, and the core heatup is delayed as much.

• 한국산학기술학회논문지
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• 제21권1호
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• pp.760-767
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• 2020

발전용 수력플랜트 분야는 기후변화 및 에너지 확보를 고려해 향후 지속적인 성장이 전망된다. 수력발전설비는 항상 수충격에 의한 위험에 노출되어 있고, 이에 대한 안정성 확보는 매우 중요하다. 수충격 현상은 밸브의 개도 조정이나 펌프와 터빈의 기동 및 정지 시 관로설비 전반에 걸쳐 발생하며, 예기치 못한 긴급 상황 시에는 더욱 현저하게 나타난다. 이와 같은 수충격에 대한 발전설비의 안정성 검토를 위해 본 연구에서는 수충격 발생 메커니즘을 반영된 특성선법을 적용한 수치해석기법(MOC-FDM: Method of Characteristic-Finite Dimensional Method, 이하 MOC-FDM)을 이용하여 전산수치 모형을 개발하였다. 개발모형은 발전설비의 주요시설인 저수지, 관로, 밸브, 펌프 등 경계조건을 반영하였고 가상시나리오 case를 적용하여 개발모형을 이용한 수치모의를 수행하였다. 개발모형 해석결과의 검증을 위해 발전설비의 주요 지점에서의 해석결과를 각각 제시하였다. 각 case 별 수충격 현상이 양호하게 재현되었으며, 상용모델의 수치해석결과와 비교분석 결과가 거의 유사하게 나타나 개발모형의 신뢰성을 확인하였다. 본 연구에서 제시된 전산수치 모델은 수력발전설비의 운영 중 발생할 수 있는 비정상상태의 유체 거동을 정교하게 예측함으로써 설비의 안정성 검토를 위한 유용한 도구로 활용될 수 있을 것으로 판단된다.

• 한국소음진동공학회논문집
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• 제23권5호
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• pp.385-393
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• 2013

In this paper, the mechanism identification and the avoidance measures on the phenomena of transient acoustic vibration amplified at the water-supply piping system to regulate the steam temperature of the boiler reheater in 500MW class supercritical power plant are presented. The pressure pulsation waves induced by the impeller passing of two feed-water pumps with five blades are coincident with the local acoustic modes of boiler reheater water-supply piping system. There are the phenomena amplified at the peaks of 5X, 10X, 15X and 20X in spectrums of piping vibration, sound pressure, and the feed-water's pressure pulsation waves. The shut-off device is installed in the piping system for the interception of pressure pulsation waves transmitted from two feed-water pumps and the modified design change of the piping layout is applied for the acoustic resonance avoidance. The acoustic natural frequencies are separated from the harmonics of pressure pulsation waves induced by the pump impellers passing through the design change of the span length. The acoustic vibration is gone by resonance avoidance measures. As a result, more than 20 dBA reduction is achieved from 100 dBA to 80 dBA.