• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.2
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• pp.119-126
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• 1999

Current transformer (CT) saturation may cause a variety of protective relays to malfunction. The conventional CT is designed that it can carry up to 20 times the rated current without exceeding 10% ratio error. However, the possibility of CT saturation still remains if the fault current contains substantial amounts of ac and/or dc components. This paper presents a design method of iron-cored CTs for use with protective relays to prevent CT saturation. The proposed design method determines the core cross section of the CT; it employs the transient dimensioning factor to consider relay's operating time (duty cycle) and dc component as well as ac components contained in the fault current, and symmetrical short-circuit current factor to consider as well as ac components contained in the fault current, and symmetrical short-circuit current factor to consider the biggest fault current. The method designs the cross section of CTs in cases of reclosure and no reclosure.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.5
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• pp.71-80
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• 2012

To improve the $NO_X$ conversion over a SCR (selective catalytic reduction) catalyst, the DOC (diesel oxidation catalyst) is usually placed upstream of the SCR catalyst to enhance the fast SCR reaction ($4NH_3+2NO+2NO_2{\rightarrow}4N_2+6H_2O$) using equimolar amounts of NO and $NO_2$. Here, a ratio of $NO_2/NO_X$ above 50% should be avoided, because the reaction with $NO_2$ only ($4NH_3+4NO+O_2{\rightarrow}4N_2+6H_2O$) is slower than the standard SCR reaction ($4NH_3+4NO+O_2{\rightarrow}4N_2+6H_2O$). In order to accurately predict the performance characteristics of SCR catalysts, it is therefore desired to develop a more simple and reliable mathematical and kinetic models on the oxidation kinetics of nitric oxide over a DOC. In the present work, the prediction accuracy and limit of three different chemical reaction kinetics models are presented to describe the chemicophysical characteristics and conversion performance of DOCs. Steady-state experiments with DOCs mounted on a light-duty four-cylinder 2.0-L turbocharged diesel engine then are performed, using an engine-dynamometer system to calibrate the kinetic parameters such as activation energies and preexponential factors of heterogeneous reactions. The reaction kinetics for NO oxidation over Pt-based catalysts is determined in conjunction with a transient one-dimensional (1D) heterogeneous plug flow reactor (PFR) model with diesel exhaust gas temperatures in the range of 115~$525^{\circ}C$ and space velocities in the range of $(0.4{\sim}6.5){\times}10^5\;h^{-1}$.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.2
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• pp.122-128
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• 2010

To meet the NOx limit without a penalty of fuel consumption, urea-SCR system is currently regarded as promising NOx reduction technology for diesel engines. SCR system has to achieve maximal NOx conversion in combination with minimal $NH_3$ slip. In this study, the performance characteristics of urea-SCR system with open loop control were assessed in the European Transient Cycle(ETC) for heavy duty diesel engine. The SCR inlet temperaure varied in the range of 200 to $340^{\circ}C$ in the ETC cycle. Open loop control calculated the urea flow rate based on the NOx and NSR map which gave for each combination of SCR inlet temperature and space velocity the normalized $NH_3$ to NOx stoichiometric ratio which resulted in a steady-state $NH_3$ slip of 20ppm. During the ETC cycle, the open loop control with the optimized NSR offset achieved NOx reduction of 80% while keeping the average $NH_3$ slip below 10ppm and maximum 20ppm. It was also found that NOx sensor was cross-sensitive to $NH_3$ and a control strategy for cross-sensitivity compensation was required in order to use a NOx sensor as feedback device.

• Journal of the Korean Vacuum Society
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• v.6 no.1
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• pp.91-96
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• 1997

The electrical characteristics and the plasma parameters of planar inductively coupled plasmas (ICP) have been measured. The resistance of the total load including the coil and the plasma varied from 1 to 4 W and the inductance from 1.5 m to 2 mH when the power was changed from 100 to 1000 W and the pressure from 1 to 10 mTorr. The density of electron measured by Langmuir probe was over $10^{11}/\textrm{cm}^3$ and the temperature varied between 3 and 5 eV as the process conditions were changed. Bias modulation was adopted as a new method to improve the selectivity of $SiO_2$on Si in $C_4F_8$ (octafluorocyclobutane) plasma. The selectivity was improved as the duty ratio decreased, but the etch rate of $SiO_2$decreased below 400$\AA$/min. $H_2$addition to $C_4F_8$ plasma showed that the etch selectivity could be higher than 50 and the etch rate of $SiO_2$over 2000$\AA$/min when 60% $H_2$was added.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.3
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• pp.232-240
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• 2016

Marine casualties originated from fishing vessels occupied about 71.2% of the whole marine casualties in Korea from 2008 to 2014, which has not changed much for a long time. Therefore, a pragmatic counterplan to decrease in casualties in fishing vessel is indispensable for reduction of marine casualties in Korea. Since the casualties occurred by fishing vessels may incline to a specific type of casualties according to the difference in the operating type; in this paper, 11 fishing types which occurred casualties frequently in numbers and occupied ratio were selected. Since the most frequent occurring casualties in fishing vessels were from collisions and fire explosion in statistics from KMST (2008~2014), the study focused on them. The collision is given a great deal of weight in all the casualties mostly due to the negligence of duty regardless of the job types. Gill netter, trap fishing boat, jig boat, multiple fishing boat and stow netter have their own specific causes of casualties in collision according to the operating types. The cause of fire explosion was mainly due to poor inspection and maintenance the electric cord. For this reason, it may be necessary for an operator to make strict precaution on the other vessels under way systematically, keep the regulation for preventing collisions, and for an engineer on watch to make a check the electricity periodically to reduce the fire explosion.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.2
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• pp.89-96
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• 2000

This paper describes the forward type pulse power supply which is the simple circuit configuration and easy to be managed using a power semiconductor switching device(Power-MOSFET) in the view of commercialization. The maximum value of output pulse voltage of the proposed pulse power supply system can be realized by the variation of phase angle($\phi$) of bridge rectifier circuit and also its pulse period is determined by the duty ratio of Power-MOSFET. The principle of basic operating and the operating characteristics of the forward type pulse power supply are estimated by the switching frequency, the variation of phase angle($\phi$)It is shown that theoretical and experimental results are in good agreement by comparing simulation and experimental results of proposed pulse power supply when a lamp type ozonizer can be used as a load. This proposed pulse power system shows that it can be practically used in the future as a power source system in various fields.

• Transactions on Electrical and Electronic Materials
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• v.6 no.6
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• pp.276-279
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• 2005

Influences of sustain pulse-width on electrical characteristics and luminous efficiency are experimentally investigated for surface discharge of AC-PDP. A square pulse with variable duty ratio and fixed rising time of 300 ns has been used in the experiment. It is found that the memory coefficient is significantly increased at the critical pulse-width. And the wall charges and wall voltages as well as capacitances are experimentally measured by Q- V analysis method along with the voltage margin relation, in terms of the sustain pulse-width in the range of $1{\mu}s$ to $5{\mu}s$ under driving frequency of 10 kHz to 180 kHz. And the luminous efficiency is also experimentally investigated in above range of sustain pulse-width with driving frequency of 10 kHz to 180 kHz. It is noted that the luminous efficiency for 10 kHz and 180 kHz are 1.29 1m/W and 0.68 1m/W respectively, since the power consumption for 10 kHz is much less than that for 180 kHz. It has been concluded that the optimal sustain pulse-width is in the range of $2.5 {\~}4.5{\mu}s$ under driving frequency range of 10 kHz and 60 kHz, and in the range of $1.5 {\~} 2.5{\mu}s$ under driving frequency range of 120 kHz and 180 kHz based on observation of memory coefficient, and wall voltage as well as luminous efficiency.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.2
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• pp.42-48
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• 2005

A DC-DC converter is being widely used for various household appliances and for industry applications. The DC-CC converter is powered from single battery, and the voltage is varied according to the purpose. In the vehicle, various accessories whose electric power is different are being un4 Thus, plural number of DC-DC converter should be provided, so these situations bring complicated circuits, and accordingly, higher cost. Under such backgrounds, in this paper, we propose a novel buck-boost chopper circuit with simply configuration which can supply to two or more different output loads. The propose chewer circuit can control output voltages by controlling duty ratio by using typically two switching devices, which is composed by single boost-switch and single buck-switch. The output voltage can be controlled widely. A few modified circuits developed from the fundamental circuit are represented including the general multi-load circuit. And all this merits and appropriateness was proved by computer simulation and experience.

• Journal of Technologic Dentistry
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• v.12 no.1
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• pp.15-21
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• 1990

This research was to investigate and study on 92 Dental Technicians who had had some experience of working or being employed at dental craft-shops or craft-rooms in Seoul area and had transferred to other types of occupation, with regard to their reasons for changing their profession. For an approach to the study, some questionnaires and interview including 3 aspects of in quiriesmental, economic and social backgrounds-were administered, and major findings are as follows ; 1. The ages in which transferring to other kinds of job happened occurred mostly from 20 to 30(78.26%) an a group of subjects whose ages ranged from 20 to 30 years old. And, with regard to their experience of working or being employed at dental craft-shops or craftrooms, the transfer of their profession to the other kinds mosty happened in a group of subjects(94.56%) whose experience of working in the dental field is less than 4 years. 2. The reason of transfer with reference to the mental background was mostly mattered in a group that expressed "Excessive Work Duties"(34.78%), and most lowly mattered in a group of subjets who had "Certain Relations with Dentists"(8.70%). Thus, it appeared that the biggest reason of transfer by the mental background was, due to the excessive duty work, not to have Sufficient time to be usualized by dental technicians for their own purpose. 3. With reference to the economical background, a group that declared there was "No Wage Standards in Ratio to Their Labor" was the most in the separation rate as shown 45.56%. And, a group suspecting "No Guarantee for Their Living after Retirement" Showed a separation rate, 9.78%. In other words, the reason for transfer was that they did not receive due wage according to their amount of labor. 4. With reference to the social background, a group making a subject for no good working environments or conditions had a separation rate, 41.30%, which was the most among others, and a group with a subject of "The Rarity of Employment because of Excessive Supply of Dental Technicians" had the rate, 10.87%, which was the lowest. This meant that the major cause of transfer by the social background was a phenomenon for dental technicans to escape from unclean working places.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.3
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• pp.355-364
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• 2013

Respect to the input AC voltage and output DC voltage, conventional three-phase PWM rectifier is classified as the voltage type rectifier with boost capability and the current type rectifier voltage with buck capability. Conventional PWM rectifier can not at the same time the boost and buck capability and its bridge is weak in the shoot- through state. These problems can be solved by Z-source PWM rectifier which has all characteristic of voltage and current type PWM rectifier. By shoot-through duty ratio control, the Z-source PWM rectifier can buck and boost at the same time, also, there is no need to consider the dead time. This paper proposes the input AC voltage sensorless control method of a three-phase Z-source PWM rectifier in order to accomplish the unity input power factor and output DC voltage control. The proposed method is estimated the input AC voltage by using input AC current and output DC voltage, hence, the sensor for the input AC voltage detection is no needed. comparison of the estimated and detected input AC voltage, estimated phase angle of the input voltage, the output DC voltage response for reference value, unity power factor, FFT(Fast Fourier Transform) of the estimated voltage and efficiency are verified by PSIM simulation.