• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.2
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• pp.215-222
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• 1999

Integrating energy storage into electlic power system has long been recognized as a way to maximize a utility's g generation and transmission capacity, Electlic power can be stored during off-peak periods and then recovered during p peak conditions to offset the need for larger generation and transmission capacity, Currently large-scale SMES for the p purpose of energystorage which can be also se$\pi$ed by battery storage or flywheel system has been developed, and near f future it will be integrated into power grids, This paper presents an investment analysis on large-scale SMES which c can determine its optimal size in power systems, In operation model. least generation cost for energy storage in SMES a and its mar밍nal capacity cost can be calculated using the discreteness of probability distribution for power availability I Investment decisions are made by the maximum p디nciple and the case study shows the optimal operation and realistic i information on the proper size of large-scale SMES in power systems.

• Journal of IKEEE
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• v.15 no.3
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• pp.198-204
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• 2011

In this letter, another analytical approach for the opportunistic amplify-and-forward (OAF) relay systems is proposed over Rayleigh fading channels. Based on set-operation at the selected relay node, its selection probability as the best relay is derived and then, the probability density function (PDF) of the received instantaneous signal-to-noise ratio (SNR) is expressed as a more tractable form in which the number of summations and the length of each summation are specified. Then, the average error rate, outage probability, and average channel capacity are obtained as approximated closed-forms. Simulation results are finally presented to validate that the proposed analytical expressions can be a unified frame work covering all Rayleigh fading channel conditions. Furthermore, it is confirmed that OAF schemes can outperform the other non-selective schemes on the average error rate, outage probability, and average channel capacity.

• The Journal of the Convergence on Culture Technology
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• v.6 no.4
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• pp.797-802
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• 2020

Over the past few years, smart devices, including smartphones, have been continuously required by users based on portability. The performance is improving. Ubiquitous computing environment and sensor network are also improved. Due to various network connection technologies, mobile terminals are widely used. Smart terminals need technology to make energy monitoring more detailed for more stable operation during use. The smart terminal which is light in small size generates the power shortage problem due to the various multimedia task among the terminal operation. Various estimation hardwares have been developed to prevent such situation in advance and to operate stable terminals. However, the method and performance of estimating the remaining amount are not relatively good. In this paper, we propose a method for estimating the remaining amount of smart terminals. The Capacity Estimation of lithium ion cells for stable operation was estimated based on machine learning. Learning the characteristics of lithium ion cells in use, not the existing hardware estimation method, through a map learning algorithm using machine learning technique The optimized results are estimated and applied.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.2
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• pp.57-63
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• 2001

This paper analysed the characteristic of Power consumption at many type of Inverter controlled Elevator. Especially, this paper proposed the standard value of full load currents. For this propose, it was classified by the passenger capacity and manufacture company. As a result, it is found that (i) the value is between -3[A] and 7[A] in case of elevator. That means the full load currents was smaller than the standard value of conventional operation type (ii) the value is between 0.5[kVA] and 3[kVA] in case of Power transformer. That means the transformer capacity was smaller than the standard value of conventional operation type. it was classified by the passenger capacity at inverter controlled elevator in apartment Also, to guarantee the operation stop of inverter controlled elevator, this paper proposed the redundancy method of electrical installations. the redundancy method is (i) 2 line service system and (ii) 2 distribution line system.

• Korean Journal of Childcare and Education
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• v.10 no.3
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• pp.31-46
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• 2014

The purpose of this study is to analyze publicness by the types of childcare centers, and factors related to publicness in the operation of childcare centers. The subjects of this study were 511 childcare centers. Data were analyzed by frequency, percentage, mean, standard deviation, F-test, Duncan's post hoc test, and regression. The findings of the study were: First, Among childcare centers, Public childcare centers were high in universality, transparency and participation. But family daycare homes and private centers were low in universality, transparency, participation, and openness. Second, public childcare centers, family daycare homes, private childcare centers, major city and medium-sized cities affected universality in the operation of childcare centers. Public childcare centers, social welfare foundation childcare centers, family daycare homes, private childcare centers and proportion of capacity affected transparency in the operation of childcare centers. Public childcare centers, family daycare homes, private childcare centers and proportion of capacity affected participation in the operation of childcare centers. Government able to accomplish publicness in the operation of childcare centers if it would strengthen management process and expanded financial for childcare centers.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.5
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• pp.1073-1077
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• 2011

The breaking capacity of circuit breakers could be no more increased in the electric power system. This is because the fault current increases due to continuous increases in electric power demand and facilities. To solve the problem, it is necessary to come up with an alternative. The superconducting fault current limiter (SFCL) has received an attention among various alternatives. The SFCL effectively reduce a fault current in cooperation with a power circuit breaker. A various types of the SFCL are suggested and a study on them have been progressed. As a result of it, the SFCL can be applyed to the electric power system in the near future. But, a study on recovery behaviors of the SFCL is not enough for applying to the electric power system. If the superconducting elements do not completely recover to the superconducting state after fault operation, it might be a breakdown of the superconducting elements due to heavy power burden and it gives an bad influence on the working of other electric devices. Additionally, the distribution power system has reclosing operation such as open-0.3sec-closed/open-3min-closed/open procedure. So we need to study more about improvement of the recovery behaviors of the SFCL. In this paper, we analyzed the recovery behaviors of a flux-coupling type SFCL according to reclosing operation when a single line-to-ground fault occurred and we compared recovery behaviors of the SFCL with and without a neutral line between secondary reactors and superconducting elements. Also, the flux-coupling type SFCL has advantageous for increases of capacity by controlling the variation in turn ratios between two reactors. Consequently, when the number of turns of the secondary reactors increased, the power burden of the superconducting elements was bigger due to the increase of impedances of the secondary reactors. To distribute the power burden, two superconducting elements connected in series and the balanced quenching of the superconducting elements was induced by connecting a neutral line.

• KCID journal
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• v.17 no.2
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• pp.57-70
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• 2010

This study was performed to analyze the affect of water supply capacity followed by allocating flood control volume in heightening reservoir, of which Baekgog reservoir was selected as a case study in here. Baekgog reservoir is located in Jincheon county, Chungbuk province, of which full water level will be heightened from EL. 100. 1m to EL. 102.1m, and total storage from 21.75M $m^3$ to 26.67M $m^3$. Flood inflow with 200year frequency was estimated to 997 $m^3$/s in peak flow and 22.54M $m^3$ in total volume. Reservoir flood routing was conducted to determine flood limited water levels, which was determined to have scenarios such as EL 97-98-99m in periods of 6.21.-7.20., 7.21.-8.20., and 8.21.-9.20., respectively, EL 97-97-97m, EL 98-98-98m in present reservoir, and EL 99-100-101m, EL 99-99-99m, and EL 100-100-100m in heightened reservoir. Reservoir inflow was simulated by DAWAST model. Annual paddy irrigation requirement was estimated to 33.19M $m^3$ to 2,975ha. Instream flow was allocated to 0.14mm/d from October to April. Operation rule curve was drawn using inflow, irrigation and instream flow requirements data. In case of withdrawal limit reservoir operation using operation rule curve, reduction rates of annual irrigation supply before and after flood control by reservoir were 2.0~4.3% in present size and 1.5~3.6% in heightened size. Reliability on water supply was decreased from 77.3% to 63.6~68.2% in present size and from 81.6% to 72.7~79.5% in heightened size. And reduction rates of water storage at the end of year before and after flood control by reservoir were 7.3~16.5% in present size and 7.7~16.9% in heightened size. But water supplies were done without any water deficiency through withdrawal limit reservoir operation in spite of low flood regulating water level.

• Journal of The Korean Association of Information Education
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• v.17 no.1
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• pp.9-21
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• 2013

The purpose of this paper is to develop and implement a mobile application system to improve arithmetical operations for low achievers. The proposed system has the following characteristics. First, the system provides individual study for low achievers based on their different study levels. Second, instant feedback can be provided to students for maintaining study motivation. Third, the system enables students to study arithmetical operations in persistent and repetitive manner. This is due to that, in the literature, arithmetical operation capacity can be increased by persistent and repetitive practices. The proposed system is applied to mathematics low achievers and the following results are obtained. First, interests and intrinsic motivation are increased through use of the proposed system. Second, arithmetical operation speed is increased. Also, accuracy of arithmetical operation is improved. Thus, it is concluded that arithmetical operation capacity of low achievers is improved using the proposed system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.1
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• pp.143-148
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• 2013

When the fault occurs in power system, the fault-current exceeds breaking capacity of the circuit breaker. So, reliablity of the power system is decreased sharply. Superconducting fault-current limiter (SFCL) is operated without impedance in normal state. The fault-current is limited by its impedance during the fault condition. However, the SFCL has several weak points such as huge size, high-price, liquid-nitrogen operation for the real power system. In this paper, We suggested the high-speed interrupter to limit the fault-current in case of the single line-to-ground fault. In addition, we compared the high-speed interrupter with the SFCL to ensure the operation reliability. The proposed interrupter detected the fault-current through the CT, and the power was supplied by operation of the SCR control system. In this experiment, the power of high-speed interrupter was applied after the 4.8[msec] from fault instant. The on-off operation of the interrupter was started after half-cycle from the fault. The fault-current was flowed into the impedance element by the switching operation of the high-speed interrupter. So, the fault current was limited within one cycle, and then it didnt exceed the capacity of a circuit breaker. We confirmed that there was slight difference between the SFCL with high-speed interrupter in terms of limiting-time of the fault-current and switching speed of the SCR. The high-speed interrupter was considered to be more efficient than the SFCL in size, cost or reliability.

• New & Renewable Energy
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• v.7 no.2
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• pp.28-35
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• 2011

Recently, photovoltaic systems have been devolved into much larger systems up to MW-scale. Photovoltaic industry participants give their focus on power generation capability of photovoltaic modules because their benefits can be decided from the amount of generation. The information on long-term performance change of photovoltaic modules helps to estimate the amount of power generation and evaluate the economic cost-benefits. Long-term performance of a PV system has been analyzed with operation data for 12 years from 1999 to 2010. In the first year, the amount of yearly power generation was 57.7 MWh with 13.2% capacity factor. In 2007, the amount of yearly generation was 44.3 MWh with 10.14% capacity factor, and in 2010, the amount was decreased down to 38.1 MWh with 8.7% capacity factor. The result means that long-term capacity factor has been 4.5% decreased for 12 years and that the amount of generation has been decreased 34.0% for 12 years which is 2.8 % per year. The latter capacity factor has been decreased faster than 0.20%, the average rate for 10 years. The performance decrease of the PV system is meant to be accelerated. The decrease of performance and utilization is due to aged deterioration of photovoltaic modules and lowering conversion efficiency of PCS.