• 한국산학기술학회논문지
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• 제6권2호
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• pp.159-164
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• 2005

광 펄스가 대기 채널을 통해 전송될 때, 대기 교란은 광 펄스를 감쇠시키고 퍼지게 한다. 이러한 감쇠와 펄스 퍼짐은 광 수신 단에서 펄스 도착시간의 요동에 의해 발생된다. 이러한 펄스 퍼짐이 인접 펄스간의 부호 간 간섭을 일으킨다. 결국, 부호 간 간섭에 의해 인접한 펄스들은 중첩이 되고 비트 전송률 및 무중계 전송거리를 제한하게 된다. 따라서, 디지털 통신시스템에서는 감쇠보다 펄스 퍼짐이 더 중요한 인자가 된다. 이에, 본 논문에서는 시간적 모멘트 함수를 이용하여 대기 교란상태에서 교란 상태를 나타내는 굴절을 구조 함수로 부호 간 간섭을 구하고, 수치 해석을 통해 교란 상태에 따른 부호 간 간섭을 나타내고자 한다.

• 한국정보통신학회논문지
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• 제17권8호
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• pp.1755-1760
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• 2013

본 논문에서는 마이크로스트립 선로를 따라 펄스가 전송될 때 분산에 의한 펄스의 왜곡특성을 시간영역에서 해석 하였다. 전송선로의 구조, 유전율에 따른 분산특성을 비교 분석하였고, 구형펄스와 가우시안 펄스에 대해 펄스의 폭과 진폭, 그리고 전송속도에 따라 분산특성을 분석하였다. 구형 펄스의 경우 더 높은 고차 고조파 성분을 가지고 있기 때문에 이에 따른 저차 고조파 성분과의 위상 속도 차이가 선로를 따라 진행함에 따라 급격히 나타나서 분산이 심하게 나타났다. 본 연구의 결과는 MIC 또는 MMIC를 설계할 때 펄스전송에서 왜곡을 최소화하기 위해 펄스 폭, 선로의 폭, 기판의 높이 그리고 유전율을 결정하는데 유용하게 사용될 것이다.

• 한국전기전자재료학회논문지
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• 제28권5호
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• pp.320-325
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• 2015

This paper dealt with a defect identification algorithm which is based on single partial discharge (PD) pulse analysis in gas insulated structure. Four types of electrode systems such as a needle-plane, a plane-needle, a free particle and a crack inside spacer were fabricated to simulate defects in gas insulated switchgear (GIS). We measured single PD pulse by an oscilloscope with a sampling rate of 5 GS/s and a frequency bandwidth of 1 GHz. Data aquisition and signal processing were controlled by a LabVIEW program. Physical shapes of PD pulses were compared with kurtosis, skewness and time-based parameters as rising time, falling time and pulse-width. These parameters were analysed by an algorithm with a back propagation algorithm (BPA). By applying the algorithm, the identification rate was 97% for the needle-plane electrode, 96% for the plane-needle electrode, 91% for the free particle and 93% for the crack inside spacer. The results verified that the algorithm could identify the type of defects in GIS.

• 한국전기전자재료학회논문지
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• 제34권2호
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• pp.136-141
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• 2021

Heating cables, widely used in office buildings, factories, streets and railways, deteriorate in electrical insulation during operation. The insulation deterioration of heating cables leads to electric discharges that can cause electrical fires. With this background, this paper dealt with a condition monitoring technique for heating cables by the analysis of discharge signals to prevent electrical fires. Insulation deterioration was simulated using an arc generator specified in UL1699 under AC operation, and the characteristic and propagation of discharge signals were analyzed on a 100 meter-long heating cable. Discharge signals produced by insulation deterioration were detected as a voltage pulse because they are as small as a few mV and they are attenuated through propagation path. The frequency spectrum of discharge signals mainly existed in the range from 70 kHz to 110 kHz, and the maximum attenuation of the signal was 84.8% at 100 meters away from the discharge point. Based on the experimental results, a monitoring device, which is composed of a high pass filter with the cut-off frequency of 70 kHz, a comparator, a wave shaper and a microprocessor, was designed and fabricated. Also, an algorithm was designed to discriminate the discharge signal in the presence of noise, compared with the pulse repetition period and the number of pulse counts per 100ms. In the experiment, the result showed that the prototype monitoring device could detect and discriminate the discharge signals produced at every discharge point on a heating cable.

• Smart Structures and Systems
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• 제26권5호
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• pp.657-666
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• 2020

A rotational pulse-echo ultrasonic propagation imager that can inspect cylindrical specimens for material nondestructive evaluations is proposed herein. In this system, a laser-generated ultrasonic bulk wave is used for inspection, which enables a clear visualization of subsurface defects with a precise reproduction of the damage shape and size. The ultrasonic waves are generated by a Q-switched laser that impinges on the outer surface of the specimen walls. The generated waves travel through the walls and their echo is detected by a Laser Doppler Vibrometer (LDV) at the same point. To obtain the optimal Signal-to-Noise Ratio (SNR) of the measured signal, the LDV requires the sensed surface to be at a right angle to the laser beam and at a predefined constant standoff distance from the laser head. For flat specimens, these constraints can be easily satisfied by performing a raster scan using a dual-axis linear stage. However, this arrangement cannot be used for cylindrical specimens owing to their curved nature. To inspect the cylindrical specimens, a circular scan technology is newly proposed for pulse-echo laser ultrasound. A rotational stage is coupled with a single-axis linear stage to inspect the desired area of the specimen. This system arrangement ensures that the standoff distance and beam incidence angle are maintained while the cylindrical specimen is being inspected. This enables the inspection of a curved specimen while maintaining the optimal SNR. The measurement result is displayed in parallel with the on-going inspection. The inspection data used in scanning are mapped from rotational coordinates to linear coordinates for visualization and post-processing of results. A graphical user interface software is implemented in C++ using a QT framework and controls all the individual blocks of the system and implements the necessary image processing, scan calculations, data acquisition, signal processing and result visualization.

• 전기학회논문지
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• 제63권5호
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• pp.629-635
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• 2014

This paper describes propagation characteristics obtained by considering semiconducting screen and cross-bonding in underground transmission cables. The semiconducting screen of power cable has effect on propagation characteristics including attenuation, velocity and surge impedance. However, it is very difficult to apply the semiconduction screen for EMTP model because of the number of conductors limitation. Therefore, CIGRE WG 21-05 proposed advanced insulation structure and analysis technique of simplified approach including inner and outer semiconducting screen. In this paper, the various propagation characteristics analyse using this structure and technique for 154kV XLPE $2000mm^2$ cable. The frequency independent model of EMTP CABLE PARAMETER is used for just pattern analysis of propagation characteristics. For exact data analysis, the frequency dependent model of J-marti is used for EMTP modeling. From these result, various propagation characteristics of 154kV XLPE $2000mm^2$ cable according to semi conducting screen consideration, frequency range, cable length and pulse width are analysed. In addition, in this paper, the effects of cross-bonding are also variously discussed according to cross-bonding methods, direct connection and impedance of lead cable.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권8호
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• pp.591-597
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• 1999

The propagation characteristics of high power microwave pulse in an air-breakdown environment are examined. The maximum electron density produced by microwave air-breakdown is limited to $10^6cm^{-3}$ by the tail-erosion effect. Inorder to increase the electron density, the scheme using two pulses intersecting at a desired height is considered. Increasing the carrier frequency, it is shown that microwave pulse can be transferred without the serious erosion in the numerical simulation. This result is useful for the above scheme. Also, an experiment is conducted to show the tail-erosion effect and confirm that a rapidly generated lossy plasma can cause spectral breaking and frequency shift of a high-power microwave pulse. The experimental results are presented by comparing the frequency spectrum of an incident pulse with that of the pulse transmitted through a self-induced air-breakdown environment. The experimental results show that the amount of frequency upshift is co-related with the ionization rate, whereas that of frequency downshift is correlated with the energy losses from the pulse in the self-generated plasma.

• 한국광학회지
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• 제6권1호
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• pp.26-32
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• 1995

Kerr cell 광스위치를 옥소 레이저 증폭단에서 짧은 펄스를 발생시키는 광절단기로서 그리고 이후의 증폭기들을 광학적으로 분리하는 격리기로 사용하였다. Kerr cell 양단에 인가된 전위차에 따른 편광의 회전에 의해 입사된 펄스를 자를 수 있음을 보였으며 회로의 전기적 특성을 이용하여 케이블의 길이차에 의해 5ns와 1ns 펄스를 발생시켰다. 공진기에서 펄스폭이 긴 펄스가 발생한 경우 한개 이상의 단축된 출력 펄스가 발생함을 확인하였다. 또한 Kerr cell의 동작전압을 변화시켜 얻은 투과도를 Kerr 이론과 비교하였다. 단축된 펄스를 옥소레이저 전 증폭기를 통해 증폭하여 4ns 펄스에서 2J의 출력을 얻어 0.5GW의 최종출력을 얻었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.1606-1607
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• 2011

In this study, the propagation characteristics of partial discharge(PD) pulses in the 3-phase cable systems including crossbonding joints were discussed. For the purpose, experiments for 22.9kV CNCV cables were performed using simulated PD pulses, and on-site partial discharge measurements were carried out for the 345kV XLPE cable system.

• 한국초전도ㆍ저온공학회논문지
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• 제1권2호
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• pp.43-48
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• 1999

The normal zone propagation (NZP) velocity and V-I characteristics of two Bi-2223 pancake coils with different Ag/SC ratio were investigated based on the experimental results and broad resistive transition were obesved in two coils. The measured NZP velocity of coil was found to be faster due to increase of Ag/SC ratio, and agree well with calculated data from two dimensional heat balance equation.