• International Journal of Korean Welding Society
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• v.4 no.1
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• pp.15-22
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• 2004

Metal transfer behavior of three shielded metal arc welding electrodes, AWS El1018, E6013 and E6010, were investigated through the characterization of size distribution of droplets and measurement of arc voltage signals. Of the three electrodes, Ell018 electrode showed the largest droplet size with the smallest amount of spatter, while E6010 electrode showed the smallest droplet size with the largest amount of spatter. Even though Ell0l8 electrode showed a good agreement between the frequencies of voltage drop in FFT processed voltage signals and the transfer rate of droplets, E6013 and E6010 electrodes showed weaker correlation because of their dominant explosive transfer behavior. The type of cathode used and electrode baking time also influenced the metal transfer behavior. Compared to bead-on-plate welding using steel plate as a cathode, welding on a water-cooled copper pipe showed less short-circuiting and higher melting rate in all electrodes because of higher arc potential and/or anode drop. When baked for a long time, E6010 electrode showed much more stable arc with less short-circuiting and explosion due to the loss of gas formation ingredients.

• Journal of Electrical Engineering and Technology
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• v.11 no.2
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• pp.446-454
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• 2016

In this paper, we present experimental results of the soil discharge characteristics as a function of moisture content when a 1.2/50-㎲ lightning impulse voltage is applied. For this study, laboratory experiments were carried out based on factors affecting the transient behavior in soils. The electrical breakdown voltages in soils were measured for a 0-6% range of moisture content for sand and a 0 - 4% range of moisture content for gravel. A test cell with semi-spherical electrodes buried face-to-face in the middle of a cylindrical container was used. The distance separating the electrodes is 100 mm. As a result, the time-lag to breakdown in soils decreases as the amplitude of applied voltage increases. The time-lag to initiation of ionization streamer is decreased, with an increase in the moisture content. However, the formative time-lag is rarely changed. The behavior of soil discharges depend not only on the type of soil and its moisture content but also on the amplitude of the impulse voltage. When the test voltage is applied repeatedly, electrical breakdown occurs along different discrete paths, leading radially away from the injected electrode. i.e., the fact that the ionization streamers propagate in different paths from shot to shot was observed.

• Journal of Hydrogen and New Energy
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• v.32 no.5
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• pp.410-416
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• 2021

The initial electrochemical performance of ceramic fuel cell with thin-film electrolyte was evaluated in terms of peak power density ratio, open circuit voltage ratio, and activation/ohmic resistance ratios at 500℃. Hydrogen and air were used as anode fuel and cathode fuel, respectively. The peak power density ratio reduced as ~17% for 40 minutes, which rapidly decreased in the early stage of the performance evaluation but gradually decreased. The open circuit voltage ratio decreased with respect time; however, its time behavior was remarkably different with the reduction behavior of the peak power density ratio. The activation resistance ratio increased as ~15% for 40 minutes, which was almost similar with the time behavior of the peak power density ratio.

• Journal of the Korean institute of surface engineering
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• v.55 no.5
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• pp.292-298
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• 2022

In this study, PEO (plasma electrolytic oxidation) film formation behavior of AZ31 Mg alloy under application of 300 Hz pulse current was studied by the analyses of V-t curve, arc generation behavior, PEO film thickness and morphology of PEO films with treatment time in 0.05 M NaOH + 0.05 M Na₂SiO₃ + 0.1 M NaF solution. PEO films was observed to grow after 10 s of application of pulse current together with generation of micro-arcs. PEO film grew linearly with treatment time at a growth rate of about 5.58 ㎛/min at 200 mA/cm² of pulse current but increasing rate of film formation voltage became lowered largely with increasing treatment time after passing about 250 V, suggesting that resistivity of PEO films during micro-arc generation decreases with increasing film formation voltage at more than 250 V.

• Journal of the Korea Safety Management & Science
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• v.3 no.4
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• pp.45-52
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• 2001

In order to Investigate water tree degradation behavior on XLPE cable, direct voltage of 200 to 800V has been applied to the material at 5$0^{\circ}C$~10$0^{\circ}C$, and the water tree property has been correlated with voltage and temperature. The leakage current was increase as temperature increased and the Ohm's law was generally satisfied in this experiment though some experimental errors were found. The leakage current was decreased and reached to the stable state with time. It was also shown that the time for the stabilization of leakage current was lessened as voltage increased

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.12
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• pp.2328-2334
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• 2009

Through the development of phasor measurement units (PMU), various aspects of power system dynamic behavior could be monitored and diagnosed. Monitoring dynamic voltage stability becomes one of achievements we can obtain from PMUs. It is very important to select the method appropriate to the KEPCO system since there are many voltage stability indices. In the paper, we propose an advanced WAVI (Wide Area Voltage Stability) for monitoring dynamic voltage stability. It reflects the PMU installation plan of KEPCO, thus it is suitable for KEPCO system specially. The salient features of the proposed index are; i) it uses only PMU measurements without coupling with EMS data. ii) it is computationally unburden so that it can be applied to real-time situation. The proposed index is applied to the KEPCO test system and the result shows that it successfully predicts voltage instability through the comparative studies.

• Journal of Electrical Engineering and Technology
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• v.4 no.4
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• pp.451-456
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• 2009

Through the development of phasor measurement units (PMU), various aspects of power system dynamic behavior could be monitored and diagnosed. Monitoring dynamic voltage stability has become one of the achievements we can obtain from PMUs. It is very important to select the most appropriate method for the Korea Electric Power Corporation (KEPCO) system since there are many voltage stability indices. In this paper, we propose an advanced WAVI (Wide Area Voltage Stability) that is well suited for the purposes of monitoring the dynamic voltage stability of KEPCO's PMU installation plan. The salient features of the proposed index are: i) it uses only PMU measurements without coupling with EMS data; ii) it is computationally unburdened and can be applied to real-time situations. The proposed index is applied to the KEPCO test system and the results show that it successfully predicts voltage instability through comparative studies.

• Journal of Hydrogen and New Energy
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• v.32 no.5
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• pp.340-346
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• 2021

The initial electrochemical performance of ceramic fuel cell with thin-film electrolyte fabricated by plasma-enhanced atomic layer deposition method was evaluated in terms of peak power density ratio, open circuit voltage ratio, and activation/ohmic resistance ratios at 500℃. Hydrogen and air were used as anode fuel and cathode fuel, respectively. The peak power density ratio reduced as ~52% for 30 min, which continually decreased as time increased but degradation rate gradually decreased. The open circuit voltage ratio decreased with respect time; however, its behavior was evidently different from the reduction behavior of the peak power density. The activation resistance ratio increased as ~127% for 30 min, which was almost similar with the reduction behavior of the peak power density ratio.

• Journal of the Korean institute of surface engineering
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• v.51 no.6
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• pp.393-399
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• 2018

Formation behavior of aluminum anodic oxide (AAO) films on Al6061 alloy was studied in view of thickness, morphology and defects in the anodic films in 20 vol.% sulfuric acid solution at a constant current density of $40mA/cm^2$, using voltage-time curve, observation of anodized specimen colors and surface and cross-sectional morphologies of anodic films with anodization time. With increasing anodizing time, voltage for film formation increased exponentially after about 12 min and its increasing rate decreased after 25 min, followed by a rapid decrease of the voltage after about 28 min. Surface color of anodized specimen became darker with increasing anodizing time up to about 20 min, while it appeared to be brighter with increasing anodizing time after 20 min. The darkened and brightened surfaces with anodizing time are attributed to an increase in thickness of porous anodic oxide film and a chemical damage of the films due to heat generated by increased resistance of the film, respectively. Cross-sectional observation of AAO films revealed the formation of defects of crack shape at the metal/oxide interface after 15 min which prevents the growth of AAO films. Width and length of the crack-like defect increased with anodizing time up to 25 min of anodizing, and finally the outer part of AAO films was partly dissolved or detached after 30 min of anodizing, resulting in non-uniform surface structures of the AAO films.

• Journal of the Korean institute of surface engineering
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• v.55 no.4
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• pp.196-201
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• 2022

This paper deals with anodic oxidation behavior of AZ31 Mg alloy in aqueous solutions containing various NaF concentrations from 0.01 M to 1 M. Three different voltage-time curves and anodic oxide formation behaviors appeared with concentration of NaF in deionized water. When NaF concentration is lower than 0.02 M, the voltage of AZ31 Mg alloy increased linearly and then reached a steady-state value more than 200 V, and large size pits and thin oxide layer were formed. When NaF concentration is between 0.05 M and 0.1 M, the voltage of AZ31 Mg alloy showed large periodic fluctuations of about 30 ~ 50 V around more than 200 V and large number of small particles were observed. If NaF concentration is higher than 0.2 M, PEO films can be formed without visible arcs under solution pH 6.5 ~ 7.5 by F^- ions without help of OH^- ions.