• 한국안전학회지
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• 제26권1호
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• pp.1-7
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• 2011

When the pumps stopped in the operation by the power failure, the hydraulic transients take place in the sudden change of a velocity of pipe line. Each and every water hammer problem shows the critical stage to be greatly affected the facts of safety and reliability in case of power failure. The field tests of the water hammer executed at Cheong-Yang booster pump station having an air chamber. The effects were studied by both the practical experiments and the CFD(Computational Fluid Dynamics : Surge 2008). The result states that the system with water hammering protection equipment was much safer when power failure happens. The following data by a computational fluid dynamic analysis are to be shown below, securing the system stability and integrity. (1) With water hammering protection equipment. (1) Change of pressure : Up to $15.5\;kg/cm^2$ in contrary to estimating $16.88\;kg/cm^2$. (2) Change rate of water level : 52~33% in contrary to estimating 55~27%. (3) Note that the operational pressure of pump runs approx. 145 m, lowering 155 m of the regularity head of pump. (4) Note that the cycle of water hammering delays from 80 second to 100 second, together with easing the function of air value at the pneumatic lines. (2) Change of pressure without water hammering protection equipment : Approximate $22.86\;kg/cm^2$. The comprehensive result says that the computational fluid dynamics analysis would match well with the practical field-test. It was able to predict Max. or Min. water hammering time in a piping system. This study aims effectively to alleviate water hammering in a pipe line to be installed with air chamber at the pumping station and results in making the stability of pump system in the end.

• 융합신호처리학회논문지
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• 제18권2호
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• pp.43-48
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• 2017

수중천이신호는 복잡하고 시변, 비선형 및 짧은 지속성의 특성을 지니고 있어서 기준패턴으로 모델링하기가 어렵다. 본 논문에서는 이러한 신호들을 프레임간의 중첩을 허용하는 일정한 짧은 신호로 잘라서 분석한다. 더빈 알고리듬을 이용하여 20차의 선형예측계수(LPC)를 프레임마다 추출하여 2층 은닉신경망회로의 입력신호로 사용한다. 추출된 선형예측계수들의 65%는 신경망구조의 학습에 이용되고 35%는 시험용 입력신호로 사용된다. 고래소리 분류에 사용된 고래 종류는 대왕고래, 들쇠고래, 귀신고래, 혹등고래, 밍크고래, 북방긴수염고래 등이다. 결과적으로 이러한 시험용의 신호들로부터 83%이상의 고래 소리 평균 분류율을 얻을 수 있었다.

• The Korean Journal of Physiology
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• 제24권2호
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• pp.377-388
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• 1990

Ca movements during the late plateau phase in rabbit atrium implicate Na-Ca exchange. In single atrial cells isolated from the rabbit the properties of the inward current of Na-Ca exchange were investigated using the whole cell voltage clamp technique. The inward currents were recorded during repolarization following brief 2 ms depolarizing pulse to +40 mV from a holding potential of -70 mV. Followings are the results obtained: 1) When stimulated every 30 sec, the inward currents were activated and reached peak values $6{\sim}12\;ms$ after the beginning of depolarizing pulse. The mean current amplitude was 342 pA/cell. 2) The current decayed spontaneously from the peak activation and the timecourse of the relaxation showed two different phases: fast and slow phase. 3) The recovery of the inward current was tested by paired pulse of various interval. The peak current recovered exponentialy with a time course similar to that of Ca current recovery. 4) Relaxation timecourse was also affected by pulse interval and time constant was reduced almost linearly according to the decrease of pulse interval between 30 sec and 1 sec. 5) The peak inward current was increased by long prepulse stimulation, Bay K, isoprenaline or c-AMP. 6) The relaxation time constant of the inward current was prolonged by Bay K or c-AMP, and shortened by isoprenaline. From the above results, it could be concluded that increase of the calcium current potentiates and prolongs intracellular calcium transients, while shortening of the timecourse by isoprenaline or short interval stimulations might be due to the facilitation of Ca uptake by SR.

• The Korean Journal of Physiology and Pharmacology
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• 제12권5호
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• pp.267-274
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• 2008

Since first discovered in chick skeletal muscles, stretch-activated channels (SACs) have been proposed as a probable mechano-transducer of the mechanical stimulus at the cellular level. Channel properties have been studied in both the single-channel and the whole-cell level. There is growing evidence to indicate that major stretch-induced changes in electrical activity are mediated by activation of these channels. We aimed to investigate the mechanism of stretch-induced automaticity by exploiting a recent mathematical model of rat atrial myocytes which had been established to reproduce cellular activities such as the action potential, $Ca^{2+}$ transients, and contractile force. The incorporation of SACs into the mathematical model, based on experimental results, successfully reproduced the repetitive firing of spontaneous action potentials by stretch. The induced automaticity was composed of two phases. The early phase was driven by increased background conductance of voltage-gated $Na^+$ channel, whereas the later phase was driven by the reverse-mode operation of $Na^+/Ca^{2+}$ exchange current secondary to the accumulation of $Na^+$ and $Ca^{2+}$ through SACs. These results of simulation successfully demonstrate how the SACs can induce automaticity in a single atrial myocyte which may act as a focus to initiate and maintain atrial fibrillation in concert with other arrhythmogenic changes in the heart.

• Journal of Electrical Engineering and Technology
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• 제9권3호
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• pp.1104-1111
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• 2014

The digital substations are being built based on the IEC 61850 network. The cooperation and protection of power system are becoming more intelligent and reliable in the environment of digital substation. This paper proposes a novel method to prevent the malfunction caused by the Transformer Magnetizing Inrush Current(TMIC) using the IEC 61850 based data sharing between the IEDs. To protect a main transformer, the current differential protection(87T) and over-current protection(50/51) are used generally. The 87T IED applies to the second harmonic blocking method to prevent the malfunction caused by the TMIC. However, the 50/51 IED may malfunction caused by the TMIC. To solve that problem, the proposed method uses a GOOSE inter-lock signal between two IEDs. The 87T IED transmits a blocking GOOSE signal to the 50/51 IED, when the TMIC is detected. The proposed method can make a cooperation of digital substation protection system more intelligent. To verify the performance of proposed method, this paper performs the real time test using the RTDS (Real Time Digital Simulator) test-bed. Using the RTDS, the power system transients are simulated, and the TMIC is generated. The performance of proposed method is verified in real-time using that actual current signals. The reaction of simulated power system responding to the operation of IEDs can be also confirmed.

• 조명전기설비학회논문지
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• 제22권9호
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• pp.94-102
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• 2008

대전 관내에서 송전계통 및 배전계통의 고장발생이 없었음에도 불구하고 고압 수용가의 2차측에서 플리커(형광등 깜박거림), 엘리베이터 정지 등의 문제가 수차례 발생하였다. 순간 전압변동의 원인을 해당 변전소 캐패시터 소손, 캐패시터 투입과 OLTC 조작으로 인한 전압변동, 고조파 공진 등을 원인으로 추정하고 같은 전압변동 원인 분석을 실시하였다. 분석 개소는 정전이 발생된 변전소 모선 전압과 전류, 캐패시터 뱅크의 전압과 전류, 덕진과 항공 D/L의 전류, 세종아파트의 MOF와 엘리베이터 전용의 변압기 2차측의 전압과 전류이다. 분석결과 변전소의 캐패시터 뱅크의 콘덴서, 리액터, 방전코일의 조사 결과 열화 및 소손이 없었으며, 4차 고조파에 공진이 되도록 설정된 것도 측정을 통해 이상 없음을 확인하였다. 사고재현을 위해 이전과 동일하게 변전소 캐패시터 조작을 수행했으나 엘리베이터가 중단되는 현상이 재현되지 않았지만 고압측의 콘덴서를 투입하였을 때 수용가측의 저압변압기 2차측에서 15[%] 이상 전압이 확대됨을 확인하였다. 다양한 분석과 시뮬레이션 결과 공진에 의해 전압이 확대되었음을 규명하였다.

• 전기학회논문지
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• 제65권8호
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• pp.1326-1333
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• 2016

It is important to clear the fault and prevent resulting in damage to power system. Although the frequency of generator internal fault is relatively low, it can lead to incalculable damage to power system as well as generator. Especially, loss of field on generator can cause the generator to lose synchronism for a short time if it is not removed promptly. Therefore, it is needed to conduct research on loss of field relay for detecting or clearing the loss of field. However, the setting of the relay may vary in generator operator or engineer, and the relay is not coordinated well with other elements associated with loss of field. In this paper, we address specifically the coordination of positive offset mho loss of field relay which is one of the protection schemes for loss of field. Computer simulations are performed by using ElectroMagnetic Transients Program-Restructured Version (EMTP-RV) based on actual data.

• Nuclear Engineering and Technology
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• 제27권4호
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• pp.483-490
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• 1995

PKL III A 4.4 실험은 "증기발생기 세관파열사고 후 소외전원 가용의 조건 하에서 발전소가 비상냉각수 주입없이 수작동에 의해 제어될 수 있음을 확인하는 것이다. 실험 모사에 따른 NLOOP Code의 제한이나 능력의 검증을 위해, 실험에서 얻어진 PKL 설비의 거동은 NLOOP의 결과와 상호 비교되었다. NLOOP 코드는 한국원자력연구소와 독일 SIEMENS/KWU사에 의해 Westinghouse 형 발전소의 과도현상 해석용으로 개발되었으며, PKL III 설비모사를 위해 적절히 수정되었다. 자연대류에 의한RCS Loop의 냉각수 유량과 격리된 RCS Loop에서의 자연대류 중단현상을 특별히 주의깊게 연구하였다. 실험과 계산 결과의 비교는 NLOOP 코드의 의사능가 문제점들을 보여준다.보여준다.

• Nuclear Engineering and Technology
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• 제50권2호
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• pp.246-252
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• 2018

A series of simulated reactivity-initiated accident (RIA) tests on irradiated fully recrystallized boiling water reactor Zircaloy-2 cladding has been performed by means of the expansion-due-to-compression (EDC) test method. The EDC method reproduces fuel pellet-clad mechanical interaction (PCMI) conditions for the cladding during RIA transients with respect to temperature and loading rates by out-of-pile mechanical testing. The tested materials had a large variation in burnup and hydrogen content (up to 907 wppm). The results of the EDC tests showed variation in the PCMI resistance of claddings with similar burnup and hydrogen content, making it difficult to clearly identify ductile-to-brittle transition temperatures. The EDC-tested samples of the present and previous work were investigated by light optical and scanning electron microscopy to study the influence of factors such as azimuthal variation of the Zr-hydrides and the presence of hydride rims and radially oriented hydrides. Two main characteristics were identified in samples with low ductility with respect to hydrogen content and test temperature: hydride rims and radial hydrides at the cladding outer surface. Crack propagation and failure modes were also studied, showing two general modes of crack propagation depending on distribution and amount of radially oriented hydrides. It was concluded that the PCMI resistance of irradiated cladding under normal conditions with homogenously distributed circumferential hydrides is high, with good margin to the RIA failure limits. To further improve safety, focus should be on conditions causing nonfavorable hydride distribution, such as hydride reorientation and formation of hydride blisters at the cladding outer surface.

• 비파괴검사학회지
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• 제23권3호
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• pp.205-211
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• 2003

구조물의 안전성평가와 관련하여 비파괴평가 방법 중에서 음향방출 (acoustic emission, AE)기법에 의한 비파괴적 결함 발생 검출 기법은 다른 기법에 비해 비교적 새로운 평가기술로서 구조물의 이상 유무를 조기에 진단하고 주기적으로 감시할 수 있는 온-라인 모니터링에 적합하다. 그러나 한편, 국내에서는 아직까지 이에 대한 체계적인 연구가 미비한 실정이며, 대부분 값비싼 외국 시스템을 도입하여 사용하고 있는 실정이다 뿐 만 아니라 기존의 음향방출 시스템은 장치의 특성상 시스템이 매우 복잡하고 가격이 고가인 관계로 다양한 산업분야에서 실제 현장에 적용하기가 쉽지 않다. 따라서 본 연구에서는 기존의 음향방출 시스템이 가지고 있던 불필요한 낭비적인 요소들을 제거하고 실제 산업현장에 부합하는 위치표정 시스템을 개발하고자 하였다. 한편, 기존의 AE 시스템들은 위치표정을 위한 신호분석이 난해할 뿐만 아니라 박판 구조물의 경우는 위치표정이 매우 어렵다. 본 연구에서는 시간-주파수 해석에 널리 사용되고 있는 웨이블릿 기법을 이용하여 보다 정확한 위치표정을 진단하는 기법을 수행하였다.