• Journal of the Korean Society for Railway
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• v.7 no.4
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• pp.412-417
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• 2004

In urban rail transit systems, ground faults in the DC traction power supply system are currently detected by the potential relay, 64P. Though it detects the fault it cannot identify the faulted region and therefore the faulted region could not be isolated properly. Therefore it could cause a power loss of the trains running on the healthy regions and the safety of the passengers in the trains could be affected adversely. Two new ground fault protective relay schemes that can identify the faulted region are presented in this paper. A current limiting device, called Device X, is newly introduced in both system, which enables large amount of ground fault current flow upon the positive line to ground fault. One type of the relaying schemes is called directional and differential ground fault protective relay which uses the current differential scheme in detecting the fault and uses the permissive signal from neighboring substation to identify the faulted region correctly. The other is called ground over current protective relay. It is similar to the ordinary over current relay but it measures the ground current at the device X not at the power feeding line, and it compares the current variation value to the ground current in Device X to identify the correct faulted line. Though both type of the relays have pros and cons and can identify the faulted region correctly, the ground over current protective relaying scheme has more advantages than the other.

• Journal of the Korean Society of Safety
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• v.33 no.5
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• pp.21-27
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• 2018

The purpose of this study is to develop a SOP (Standard Operating Procedure) for a distribution board that can monitor the leakage current of a load distribution line in real time. The developed distribution board was fabricated by applying IEC 61439-1. It consists of the distribution board and an alarm device. The work process for making the distribution board was compliant with the KEMC (Korea Electrical Manufacturers Cooperative) regulations. And the AC distribution board range is 1,000 V. In addition, the voltage in DC is less than 1500 V. The distribution board receives a 3-phases and 4-wires power supply system and can supply power to the load of a maximum of 32 single or three phase distribution circuits. Also, leakage current measured on the power distribution board was used by sensors installed. The SOP of the developed distribution board consists of the installation standards for the short circuit alarm device and sensor, the surge protection device, switches and indication lamps, and other devices. The operation procedure was prepared so that each manufacturing step of the distribution board must be confirmed by the persons in charge of preparation, production, quality control and approval before moving forward to the next step.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.385-386
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• 2015

This paper analyzes the vulnerable area according to the configuration of Low Voltage DC (LVDC) distribution system. For this study, the various types of system layout are considered and the simulation results are presented.

• Electrical & Electronic Materials
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• v.11 no.11
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• pp.17-21
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• 1998

The surface potential distribution on insulating polymers was measured by scanning of the probe of an electrostatic voltmeter. The measurements were done for two measured by scanning of the probe of an electrostatis voltmeter. The measurements were done for two cases. In the first case, it was measured on the free surface of insulating films which had been inserted between plane electodes after the removal of the upper brass disk electrode. In the second case, we measured the charging region between a circular and its opposing concentric ring electrodes after the removal of dc ramp voltage in air and nitrogen gas.

• Bulletin of the Korean Chemical Society
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• v.15 no.5
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• pp.349-353
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• 1994

The CN radical was generated in a jet with an inert buffer gas, helium from high voltage dc discharge of the precursor $CH_3CN$. The Fourier transform emission spectra of the O-O band of the $(B^2{\Sigma}^+{\to}X^2{\Sigma}^+)$ transition of CN have been obtained with a Bruker IFS-120HR spectrometer. The spectra show an anomalous distribution of rotational intensity which cannot be explained by a simple Boltzmann distribution. The analysis of the transition frequencies provides molecular constants with high accuracy for both the ground and the excited electronic states of the CN radical.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.67 no.3
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• pp.119-124
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• 2018

Recently, LVDC distribution network and DC microgrid with many advantages are being built. However, this LVDC distribution is an IT grounded or ungrounded system, and it is difficult to detect a ground fault because the fault current is small. In this paper, we propose a signal injection method for unipolar LVDC distribution network to detect ground fault in ungrounded LVDC distribution, and various analyzes were performed for ground fault detection.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.685-688
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• 2000

Pulse plating is about to deposit material at high current density compared to conventional DC plating. For example pulse plating can get more fine grain can improve adhension and metal distribution and current efficiency can reduce internal stress and crack. therefore we studied pulsed power supply which has high current density and improve deposition quality and increase plating speed in this paper.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1124-1128
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• 2021

As regulations of emissions from ships become more stringent, electric propulsion systems have been increasingly used to solve this problem in vessels ranging from large merchant ships to small and medium-sized ships. Methods for improving the efficiency of the electric propulsion system include the improvement of power sources; the use of a system linked to environmentally friendly power sources, such as batteries, fuel cells, and solar power; and the development of hardware and control methodology for rectifiers, power conversion devices, and propulsion motors. The method using a phase-shifting transformer with diodes has been widely used for rectification. Power semiconductor devices with grid connection to an environmentally friendly power source using DC distribution, a variable speed power source, and the application of small and medium-sized electric propulsion systems have been developed. Accordingly, the demand for active front-end (AFE) rectifiers is increasing. In this study, a method using a neural network rather than a conventional proportional-integral controller was proposed to control the AFE rectifier. Tested controller data were used to design a neural network controller trained through MATLAB/Simulink. The neural network controller was applied to a rectification system designed using PSIM software. The results indicated the effectiveness of improving the waveform and power factor DC output stage according to the load variation. The proposed system can be applied as a rectification system for small and medium-sized environmentally friendly ships.

• Korean Journal of Optics and Photonics
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• v.14 no.1
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• pp.23-32
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• 2003

The spectroe-ellipsometric constant $\Delta$, Ψ and the ellipsometric growth curves at the wavelength of 632.8 nm are collected. These are critically examined to find out the optimum growth condition of phase change $Ge_2Sb_2Te_5(GST)$ thin films as an optical recording medium. GST films are prepared using DC magnetron sputtering technique, under the selected experimental conditions of Ar gas pressure (5 mTorr, 7 mTorr and 10 mTorr), DC power of sputtering gun (15 W, 30 W and 45 W), and substrate temperature (from room temperature to 18$0^{\circ}C$). Based on the three film model, the density distribution of deposited GST films are obtained versus Ar gas pressure and DC power by analyzing spectro-ellipsometric data. The calculated evolution curves at the wavelength of 632.8 nm, are fit into the in situ observed ones to get information about the evolution of density distribution during film growth. The density distribution showed different evolution curves depending on deposition conditions. The GST films fabricated at DC power of 30 W or 45 W, and at Ar gas pressure of 7 mTorr turned out to be the most homogeneous one out of those prepared at room temperature, even though the maximum density difference between the dense region and the dilute region of the GST film was still significant (~50%). Finally, in order to find the optimum growth condition of homogeneous GST thin films, the substrate temperature is varied while Ar gas pressure is fixed at 7 mTorr and DC power at 30 W and 45 W respectively. A monotonic decrease of void fraction except for a slight increase at 18$0^{\circ}C$ is observed as the substrate temperature increases. Decrease of void fraction indicates an increase of film density and hence an improvement of film homogeneity. The optimum condition of the most homogeneous GST film growth turned out to be 7 mTorr of Ar gas pressure, 15$0^{\circ}C$ of substrate temperature. and 45 W of DC power. The microscopic images obtained using scanning electron microscope, of the samples prepared at the optimum growth condition, confirmed this conclusion. It is believed that the fabrication of homogeneous GST films will be quite beneficial to provide a reliable optical recording medium compatible with repeated write/erase cycles.

• Journal of the Korean Magnetics Society
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• v.13 no.2
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• pp.47-52
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• 2003

Ferromagnetic tunnel junctions were fabricated by dc magnetron sputtering and plasma oxidation process. The local transport properties of the ferromagnetic tunnel junctions were studied using contact-mode Atomic Force Microscopy (AFM) and the local current-voltage analysis. Tunnel junctions with the structure of sub./Ta/Cu/Ta/NiFe/Cu/Mn$\_$75/Ir$\_$25//Co$\_$70/Fe$\_$30//Al-oxide were prepared on thermally oxidized Si wafers. Al-oxide layers were formed with microwave excited plasma using radial line slot antenna (RLSA) for 5 and 7 sec. Kr gas was used as the inert gas mixed with $O_2$ gas for the plasma oxidization. No correlation between topography and current image was observed while they were measured simultaneously. The local current distribution was well identified with the distribution of local barrier height. Assuming the gaussian distribution of the local barrier height, the ferromagnetic tunnel junction with longer oxidation time was well fitted with the experimental results. As contrast, in the case of the shorter time oxidation junction, the current mainly flow through the low barrier height area for its insufficient oxygen. Such leakage current might result in the decrease of tunnel magnetoresistance (TMR) ratio.