• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.147-148
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• 2008

In this paper two kinds of techniques were compared for localization of PD(partial discharge) in power transformer and more useful method was suggested. Both of them, the time of arrival and the energy content method, were tested in 154kV single phase experimental transformer using UHF signal measurement. The former was using the difference of arrival time of recorded signals from four UHF sensors, the latter was based on the energy content in frequency spectra of signals detected at all sensors.

• Journal of Electrical Engineering and Technology
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• v.12 no.1
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• pp.19-28
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• 2017

False data injection attacks have recently been introduced as one of important issues related to cyber-attacks on electric power grids. These attacks aim to compromise the readings of multiple power meters in order to mislead the operation and control centers. Recent studies have shown that if a malicious attacker has complete knowledge of the power grid topology and branch admittances, s/he can adjust the false data injection attack such that the attack remains undetected and successfully passes the bad data detection tests that are used in power system state estimation. In this paper, we investigate that a practical false data injection attack is essentially a cyber-attack with uncertain information due to the attackers lack of knowledge with respect to the power grid parameters because the attacker has limited physical access to electric facilities and limited resources to compromise meters. We mathematically formulated a method of identifying the most vulnerable locations to false data injection attack. Furthermore, we suggest minimum topology changes or phasor measurement units (PMUs) installation in the given power grids for mitigating such attacks and indicate a new security metrics that can compare different power grid topologies. The proposed metrics for performance is verified in standard IEEE 30-bus system. We show that the robustness of grids can be improved dramatically with minimum topology changes and low cost.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.12
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• pp.1142-1149
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• 2003

The strength and characteristics of the soldering interface of the power semiconductor chip in a power module has been firstly surveyed by the peel strength measurement method. A power module is combined with several power chips which generally has 30∼400$\textrm{mm}^2$ chip area to allow several tens or bigger amps in current rating, so that the traditional methods for interface characterization like shear test could not be applied to high power module. In this study power diode modules were fabricated by using lead-tin solder with 10${\times}$10$\textrm{mm}^2$ or 7${\times}$7$\textrm{mm}^2$ soldering interface. The peel strengths of soldered interfaces were measured and then the microscopic investigation on the fractured surfaces were followed. The peel test indicated that the crack propagated either through the bulk of the soft lead-tin solder which has 55-60 kgf/cm peel strength or along the interface between the solder and the plated nickel layer which has much lower 22 kgf/cm strength. This study showed that the peel test would be a useful method to quantify the solderability as well as to recognize which is the worst interface or the softest material in a power module with a large soldering area.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.4
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• pp.293-297
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• 2020

This paper tried to find the best conditions that could be applied to solar cells by deposition of CdS thin film on ITO glass using multiplex displacement sputter system. RF power was changed to 50W, 100W, and 150W and sputtering time was set to 10 minutes. As a result of the measurement of transmittance, the average transmittance in the area of 400 to 800 nm was measured from 60% to 80% and the best characteristic was measured at 150W at 84%. The band gap was also measured at 3.762eV at 50W, 4.037eV at 100W and 4.052eV at 150W. In XRD analysis, even as RF power was increased, it was observed as a structure called Wurtzite (hexagonal) of CdS. And as RF power increased, the particles were large and uniformly deposited, but at 100W the particles were densely composed and dense. And the thickness measurement showed that the RF power increased uniformly.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.93.1-93.1
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• 2005

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.481-482
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• 2012

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.130-130
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• 2003

• 제어로봇시스템학회:학술대회논문집
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• 1987.10b
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• pp.174-178
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• 1987

In the design of reference model based STC (self-tuning controllers), parameters of the controllers are determined not from the true plant but from the estimated model. In this paper, we suggest a power spectrum estimation method for visualling the sensitivity of the closed loop system without knowing the explicit original plant.

• Journal of Power System Engineering
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• v.7 no.3
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• pp.5-11
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• 2003

• 한국초전도학회:학술대회논문집
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• 2008.08a
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• pp.42-42
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• 2008