• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.426-430
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• 2003

본 연구에서는 초음파현미경의 기하학적 원리와 초음파현미경의 특징중 하나인 V(z)곡선의 간섭파형을 시뮬레이션 하였고, 실제 초음파현미경의 V(z)곡선법을 이용하여 미소영역에서의 누설탄성표면파 음속을 측정하였다. 초음파현미경을 이용한 V(z)곡선법의 음속측정결과가 시뮬레이션 음속값과 큰차이를 보이지 않으므로 미소영역에 초음파현미경의 V(z)곡선법을 적용하여 초음파의 음속측정이 가능함을 확인하였다. 이는 향후 초음파현미경을 이용하여 미세한 재료의 물성평가에 적용할 수 있을 것으로 기대된다.

• Journal of Power System Engineering
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• v.13 no.1
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• pp.39-45
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• 2009

The attenuation of the fundamental non-torsional modes that propagate down buried steel water pipes has been studied. The mode shapes, mode attenuation due to leakage into the surrounding medium and the scattering of the modes as they interact with pipe joints and fittings have been investigated. In the low frequency region the mode predicted to dominate over significant propagation distances approximates a plane wave in the water within pipe. The established acoustic technique used to locate leaks in buried steel water pipes assumes that leak noise propagates as a single non-dispersive mode at a velocity related to the low frequency asymptote of this water borne mode.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.33-34
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• 2010

본 논문에서는 기 제작된 전기자동차용 고효율 승압형 양방향 DC/DC 컨버터의 소형/경량화 및 전력밀도의 상승을 위한 구조설계를 제안한다. 제안된 컨버터는 1차 측 Full-Bridge 회로와 고조파 변압기 부, 2차 측 배압회로를 구성하고 변압기에 존재하는 누설인덕턴스 성분과 배압회로의 커패시터 성분을 이용하여 직렬 L-C공진회로를 구성함으로서 모든 스위치에 ZCS (Zero Current Switching)을 구현하여 전체 사이즈 및 비용을 감소시키고자 하였다. 제안된 방식의 타당성을 입증하기 위하여 전력밀도의 비교 및 PSIM 시뮬레이션으로 본 논문에서 제안된 컨버터 구조의 타당성을 검증하고자 한다.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.31-32
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• 2010

본 논문에서는 에너지 순환을 위해 회생제동을 할 수 있는 전기자동차용 고효율 승압형 양방향 DC/DC 컨버터를 제안한다. 제안된 컨버터는 1차 측 Full-Bridge 회로와 고조파 변압기 부, 2차 측 배압회로를 구성하고 변압기에 존재하는 누설인덕턴스 성분과 배압회로의 커패시터 성분을 이용하여 직렬 L-C공진회로를 구성함으로서 모든 스위치에 ZCS (Zero Current Switching) 을 구현함으로서 전체 사이즈 및 비용을 감소시키고자 하였다. 제안된 방식의 타당성을 입증하기 위하여 PSIM 시뮬레이션으로 본 논문의 컨버터 구조의 타당성을 검증하고자 한다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.9
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• pp.1013-1021
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• 2004

This paper presents the results of spectrum analysis of leakage current waveforms on contaminated polymer insulators under fog conditions. This is a basic study on development of a monitoring for aging degree and surface pollution state using distortion rate(%) of 3rd and 5th harmonics according fundamental frequency[60Hz] under environment conditions. Arcing on the surface was always associated with distortion in the leakage current ; hence the low frequency components of the leakage current can be used as a means to evaluate the surface degradation. The results indicate that the distortion rate by spectrum analysis is available for the monitoring of contamination condition of EPDM Polymer insulators.

• Proceedings of the KIEE Conference
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• 1998.07e
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• pp.1740-1742
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• 1998

This paper describes the technique of deterioration diagnosis for ZnO element. Due to the non-linear resistance of ZnO block, the total leakage current contains harmonics when arrester deteriorated. The most significant harmonics is the 3rd order component. So, it can be used as an indicator of the arrester condition. An iron core, which has a very high relative permeability, is used for increasing detection sensitivity and the 3th order harmonics of leakage current was detected by band-pass circuit. And we have verified the reliability and performance of the sensing device through several laboratory tests.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.297-298
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• 2013

본 논문에서는 LLC 공진형 컨버터의 트랜스포머를 Cantilever 모델로 등가화하여 공진 네트워크를 설계하기 위한 과정을 제시한다. 트랜스포머의 결합계수를 고려하여 누설 인덕턴스와 자화인덕턴스의 크기를 계산한다. 그 결과로 얻어진 파라미터를 이용하여 기본파 분석 (First Harmonic Approximation, FHA)을 통해 LLC 공진형 컨버터의 전압 이득관계를 분석한다. 제시한 설계방법을 적용하여 500W급 LLC 공진형 컨버터를 제작 구현함으로써 설계과정의 타당성을 검증한다.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.336-341
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• 2004

This research investigates the feasibility of ultrasonic microscope for nondestructive assessment of thermal degradation in artificially aged commercial Co-base superalloy, FSX414. This alloy has been used for high temperature structure applications such as stationary gas turbine blade and nozzle chamber in fossil plant. Microstructural change was found that the fine carbides became coarser and spheroidized in matrix as aging time increased. The leaky surface acoustic wave velocity gradually decreases by a maximum of 4.7% with increasing aging time up to 4,000hours. However, the longitudinal wave velocity has a little change. Also, it has a good correlation between leaky surface acoustic wave velocity and Vickers hardness. Consequently, LSAW can be used to examine the degree of degradation in thermally aged Co-base superalloy.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.12
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• pp.9-14
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• 2000

A numerical method for scattering of electromagnetic waves from a arbitrary shaped grating covered with dielectric slab is considered for TE polarization case from the viewpoints of both reflection grating problem and leaky wave antenna problem. The analysis is based on a periodic Green's function and the method of moments. Numerical results involving some combinations of geometric parameters are presented in terms of relative scattered powers of spectral modes and complex propagation constants.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.9
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• pp.1306-1313
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• 2012

This paper reports the contamination performance of two distribution arresters (new and used ones) tested under three different contaminant conditions - clean fog, ESDD (equivalent salt deposit density) level (A, B, C, and D), and kaolin contamination conditions, and their leakage current, total leakage current, and component of the resistive leakage current were measured in order to diagnose arrester deterioration. The 3rd harmonics was larger than 5th and 7th ones for the arrester under the clean fog, and as the ESDD contamination level was applied, 5th one became relatively larger than 3rd one. Therefore, these results indicated that the resistive leakage current could be used for the diagnosis of the arresters.