• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.69-70
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• 2008

Automatic control systems(AVR, Governor, Synchronizer) installed $1970{\sim}1980$ in K-water were considered to be rehabilitated around 2000. Moreover, Korea Power Exchange market system was changed from PPA (Power Purchase Agreement) to a bidding system. Therefore, depending on the power quality, the power provider could achieve additional profits. It is the excitation system and governor that have the functions of enhancing power necessities. During the 20 to 30 years of generator operation, there were many major and minor problems. Examples are SCR burnout (Andong: Excitation system), hunting (Imha: governor), field circuit breaker failure (Chungju 1st: excitation system), the rise of leakage current (Chungju 2nd: excitation system), power supply burnout (Chungju 2nd: governor). These are the typical examples of malfunction which hindered the generator operation and, consequently, diminished the profit of power business. In order to satisfy the needs of the power market and prevent malfunctions mentioned above, the rehabilitation of AVRs and governors were executed. A new system was made to have the flexibility of ancillary service (GF, AGC, etc.), PSS function. With user friendly HMI software, it is more convenient for the operator to fulfill suitable maintenance. It was possible to connect SCADA system by opening protocol of AVR, governor for the efficiency of operation and maintenance.

• Proceedings of the KAIS Fall Conference
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• 2003.06a
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• pp.267-270
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• 2003

All artificial infernal organs which are using electric energy supply energy with inductive couple. Transcutaneous energy transmission system enhance survival chance of the patients and quality of life by reducing volume and mass. In this research, we used both tune in transmission system in state of fixing cycle in order to increase the voltage gain and the current gain and to reduce effect of leakage inductance. Also to maximize the effect of resonance, a constant frequency duty cycle control method is used. Test is progressed with litz wire which is set up with various sizes of core to minimize size of converter. This research aimed in analysis of transcutaneous energy transmission system and in measuring of stability and efficiency of Lithium-ion battery charge which are using transmitted energy.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.2224-2236
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• 2014

The performance of an isolated high voltage full bridge converter is improved using a voltage doubler. In a conventional high voltage full bridge converter, the diode of the transformer secondary voltage undergoes a voltage spike due to the leakage inductance of the transformer and the resonance occurring with the parasitic capacitance of the diode. In addition, in the phase shift control, conduction loss largely increases from the freewheeling mode because of the circulating current. The efficiency of the converter is thus reduced. However, in the proposed converter, the high voltage dual converter consists of a voltage doubler because the circulating current of the converter is reduced to increase efficiency. On the other hand, in the proposed converter, an input current is distributed when using parallel input / serial output and the output voltage can be doubled. However, the voltages in the 2 serial DC links might be unbalanced due to line impedance, passive and active components impedance, and sensor error. Considering these problems, DC injection is performed due to the complementary operations of half bridge inverters as well as the disadvantage of the unbalance in the DC link. Therefore, the serial output of the converter needs to control the balance of the algorithm. In this paper, the performance of the conventional converter is improved and a balance control algorithm is proposed for the proposed converter. Also, the system of the 1.5[kW] PCS is verified through an experiment examining the operation and stability.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.2
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• pp.225-232
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• 1994

In this paper, a new approach for the induction machine control whih ensures producing maximum torque per ampere over the entire field weakening region is presented. In addition, the relation of the output torque capability with the leakage factor of the machine is examined. Also the smooth and precise transition into the field weakening operation can be achieved by adjusting the base speed for the field weakening operation according to the flux level, the current limit and the voltage limit. The proposed is verified through simulation and experiment for a 5hp laboratory induction motor drive system.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1369-1371
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• 2001

This paper describes on thinning SDB SOI substrates by SDB technology and Electro-chemical etch-stop. The surface of the fabricated SDB SOI substrates is more uniform than that grinding or polishing by mechanical method, and this process is possible to accurate SOI thickness control. During Electrochemical etch-stop, leakage current versus voltage curves were measured for analysis of the open current potential (OCP) point and the passivation potential (PP) poin and determinated to anodic passivation potential. The surface roughness and selectively controlled thickness of the fabricated SOI substrates were analyzed by using AFM and SEM, respectively.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.3 no.5
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• pp.548-574
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• 2009

Personal information (hereinafter referred to as "PI") infringement has recently emerged as a serious social problem in Korea. PI infringement in the public and private sector is common. There were 182,666 cases of PI in 2,624 public organizations during the last three years. Online infringement cases have increased. PI leakage causes moral and economic damage and is an impediment to public confidence in public organizations seeking to manage e-government and maintain open and aboveboard administration. Thus, it is an important matter. Most cases of PI leakage result from unsatisfactory management of security, errors in home page design and insufficient system protection management. Protection management, such as encryption or management of access logs should be reinforced urgently. However, it is difficult to comprehend the scope of practical technology management satisfied legislation and regulations. Substantial protective countermeasures, such as access control, certification, log management and encryption need to be established. It is hard to deal with the massive leakage of PI and its security management. Therefore, in this study, we analyzed the conditions for the technical protection measures during the processing phase of PI. In addition, we classified the standard control items of protective measures suited to public circumstances. Therefore, this study provides a standard and checklist by which staff in public organizations can protect PI via technical management activities appropriate to laws and ordinances. In addition, this can lead to more detailed and clearer instructions on how to carry out technical protection measures and to evaluate the current status.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.371-372
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• 2007

The major causes of electrical fire are classified to short circuit fault, overload fault, electric leakage and electric contact failure. The occurrence factor of the fire is electric arc or spark accompanied with electrical faults. Residual Current Protective Device (RCD), that is Earth Leakage Circuit Breaker(ELB) and Molded_case Circuit Breaker (MCB), of high sensitivity type used at low voltage wiring cuts off earth leakage and overload, but the RCD can't cut off electric arc or spark to be a major factor of electrical fire. As the RCDs which are applied low voltage distribution panel are prescribed to rated breaking time about 30[ms] (KS C 4613), the RCDs can't perceive to the periodic electric arc or spark of more short wavelength level. To be improved on such problem, this research development is proposed to a auxiliary control apparatus for RCD trip on electric arc or spark due to electrical fire. Some experimental results of the proposed apparatus is confirmed to the validity of the analytical results.

• Convergence Security Journal
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• v.18 no.3
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• pp.77-85
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• 2018

With the convergence of communications network between control system and public network, such threats like information leakage/falsification could be fully shown in control system through diverse routes. Due to the recent diversification of security issues and violation cases of new attack techniques, the security system based on the information database that simply blocks and identifies, is not good enough to cope with the new types of threat. The current control system operates its security system focusing on the outside threats to the inside, and it is insufficient to detect the security threats by insiders with　the authority of security access. Thus, this study conducted the importance analysis based on the main event log list of "Spotting the Adversary with Windows Event Log Monitoring" announced by NSA. In the results, the matter of importance of event log for the detection of insider threats to control system was understood, and the results of this study could be contributing to researches in this area.

• Transactions on Electrical and Electronic Materials
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• v.10 no.5
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• pp.152-155
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• 2009

The microstructure and the electrical properties of a ZnO varistor, which was composed of a ZnO-$Bi_2O_3$-$Sb_2O_3$-CoO- $MnO_2$ -NiO-$Nd_2O_3$ system, were investigated at various $Y_2O_3$ addition concentrations. $Y_2O_3$ played a role in the inhibition of the grain growth. As the $Y_2O_3$ content increased, the average grain size decreased from $6.8{\mu}m$ to $4{\mu}m$, and the varistor voltage($V_{1mA}$) greatly increased from 275 to 400 V/mm. The nonlinearity coefficient ($\alpha$) decreased from 72 to 65 with increasing $Y_2O_3$ amount. On the other hand, the leakage current ($I_L$) increased from 0.2 to 0.9 ${\mu}A$. These results confirmed that doping the varistors with $Y_2O_3$ is a promising production route for production of a higher fine-grained varistor voltage ($V_{1mA}$) which can dramatically reduce the size of the varistors.

• Journal of the Korean Institute of Gas
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• v.8 no.1 s.22
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• pp.30-36
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• 2004

Although the usage of gas as one of the most economical energy source is ever expanding, numerous gas accidents occur as a result of negligence in safety management. The main reason behind such accident is that the current safety control system relies heavily on the manual control mechanism. This paper designed and developed a prototype of a computerized gas safety control system that automates such critical functions as the alarm sensing and the valve control. Since the system is connected through a digital network, the control can be performed remotely. Most importantly, the accidental risk or damage can be greatly reduced since the system monitors and reacts actively to gas leakage in real time.