• Journal of the Korean Society for Railway
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• v.20 no.1
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• pp.31-42
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• 2017

Many studies have been performed to reduce electric consumption in railway systems. Due to its low conduction loss and high regenerative braking efficiency characteristics, the ESS powered railway system is chosen as a promising candidate for future railway systems. This paper introduces the ESS powered railway system and analyzes current power charge calculation methods that have been set up by KEPCO (Korea Electric Power Corporation). Based on the analysis, this paper proposes two different power charge reduction methods for the railway system. One is to smooth the peaks of traction energy consumption by supplying additional energy to the grid. The other is to save electric charge by reducing electric energy consumed by the railway during the energy peak time, 2 p.m.~5 p.m., which has highest 'Won/kWh' rates. To verify the effectiveness of the proposed method, the power charge of Seoul Metro Line 2 is recalculated using the method.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.6
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• pp.67-74
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• 2010

Most of domestic low-voltage consumers are supplied from the TN-C system of KEPCO, but their load installations have established according to the national statutory standard for electrical installations based on the TT system. In this work, to propose the proper system earthing arrangements of ensuring the protection of information-technology equipment against lightning surges, the protection performance of TT and TN systems against lightning surges was investigated. As a result, when lightning surge was injected to the neutral line of distribution system, the potential difference between the equipment earth terminal and neutral point of low-voltage mains in a TT system was significantly raised. The TT system is not advised due to the risk of damage to the sensitive computer equipment. Main equipotential bonding is an important requirement for protection of low-voltage installations against lightning surges. The TN system provides the best means to reduce the incoming lightning surges through the neutral line of low-voltage service systems. In addition, It is highly recommended to install the additional earthing at the service position of low-voltage consumers.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.1
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• pp.1-7
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• 2007

Generally, an electric railroad feeding system has many problems due to the different characteristics in contrast with a load of general three-phase AC electric power system. One of them is harmonics problem caused by the switching device existing in the feeding system, and moreover, the time-varying dynamic loads of rail way is inherently another cause to increase this harmonics problem. In Korea power systems, the electric railroad feeding system is directly supplied from the substation of KEPCO. Therefore, if voltages fluctuation or unbalanced voltages are created by the voltage and current distortion or voltage drop during operation, it affects directly the source of supply. The trainloads of electric railway system have non-periodic but iterative harmonic characteristics as operating condition, because the electric characteristic of the electric railroad feeding system is changed by physical conditions of the each trainload. According to the traditional study, the estimation of harmonics has been performed by deterministic way using the steady state data at the specific time. This method is easy to analyze harmonics, but it has limits in some cases which needs an assessment of dynamic load and reliability. Therefore, this paper proposes the probabilistic estimation method, moments matching method(MW) in order to overcome the drawback of deterministic method. In this paper, distributions for each harmonics are convolved to obtain the moments and cumulants of TDD(Total Demand Distortion), and this can be generalized for any number of trains. For the case study, the electric railway system of LAT(Intra Airport Transit) in Incheon International Airport is modeled using PSCAD/EMTDC dynamic simulator. The raw data of harmonics for the moments matching method is acquired from simulation of the LAT model.

• Journal of IKEEE
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• v.23 no.1
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• pp.188-192
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• 2019

As the contribution of the Energy Storage System (ESS) on the power system operations has increased, it is required to secure the reliability on the capacity of ESS and this needs to consider the outage rate in calculating the available capacity of ESS. However, the existing method of calculating the outage rate does not consider the configuration of ESS and this does not accurately calculate the available capacity of ESS. For this, this paper analyzes the structural characteristics of ESS in Korean power system and proposes a method to calculate the outage rate of ESS. Through the study cases adopting the Korea Electric Power Corporation (KEPCO) ESS for providing the frequency response service, the effectiveness of the proposed method verified.

• Journal of Internet Computing and Services
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• v.20 no.2
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• pp.51-59
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• 2019

In this paper, we analyzed the relationship between charging operation system and electricity charges connected with charging infrastructure among data of many demonstration projects focused on electric vehicles recently. At this point in time, due to the rapid increase in demand for the electric charging infrastructure that will take place in the future, we can prepare for an upcoming era in the sense of forecasting the demand value. At the same time, demonstrating and modeling optimized system modeling centering on sites is a prerequisite. The modeling based on the existing small - scale simulation and the design of the operating system are based on the data linkage analysis. In this paper, we implemented a new optimized system modeling and introduced it as a standard format to analyze time - dependent time - divisional data for each vehicle and user in each point and node. In order to verify the efficiency of the optimization based on the data linkage analysis for the actual implemented electric car charging infrastructure and operation system.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.5
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• pp.533-538
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• 2004

This paper proposes a systematic method to develop short-term electrical load forecasting systems using neuro-fuzzy models. The proposed system predicts the electrical loads with the lead times of 1 hour, 24 hour, and 168 hour. To do so, the load forecasting system first builds an initial structure off-line for each hour of four day types and then stores the resultant initial structures in the initial structure bank. 96 initial structures are constructed for each prediction lead time. Whenever a prediction needs to be made, the proposed system initializes the neuro-fuzzy model with the appropriate initial structure stored and trains the initialized prediction modell. To improve the performance of the prediction system in terms of accuracy and reliability at the same time, the prediction model employs only two inputs. It makes possible to interpret the fuzzy rules to be learned. In order to demonstrate the viability of the proposed method, we develop a load forecasting system by using the real load data collected during 1996 and 1997 at KEPCO. Simulation results reveal that the prediction system developed in this paper can achieve a remarkable improvement on both accuracy and reliability

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.8
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• pp.1024-1030
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• 2018

Recently, the large scaled energy storage system(ESS) which has various functions such as peak saving, demand management, output stabilization of renewable energy and frequency regulation(FR) is being energetically installed and operated. Especially, as the use case of frequency regulation ESS, the KEPCO has demonstrated the total of 376[MW] ESS since 2014. However, there are no operational experiences and international technical standards on frequency regulation application in ESS. Therefore, this paper propose the evaluation algorithm for power system performance of ESS by considering the frequency characteristics between governor of existing generator and frequency regulation ESS, in order to verify the power system performance of ESS. And also, this paper propose an evaluation modeling for small scaled power system including the existing generator, frequency control ESS and customer loads based on the PSCAD/EMTDC S/W. From the simulation results in 360[MW] model power system, it is confirmed that frequency regulation ESS has better performances than conventional generators.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.1
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• pp.85-91
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• 2017

To develop a pressurized chemical looping combustor, effect of pressure on minimum fluidization velocity and transition velocity to fast fluidization was investigated in a two-interconnected pressurized fluidized bed system using oxygen carrier particle. The minimum fluidization velocity was measured by bed pressure drop measurement with variation of gas velocity. The measured minimum fluidization velocity decreased as the pressure increased. The transition velocity to fast fluidization was measured by emptying time method and decreased as the pressure increased. Gas velocity in the fuel reactor should be greater than the minimum fluidization velocity and gas velocity in the air reactor should be greater than the transition velocity to fast fluidization to ensure proper operation of two interconnected fluidized bed system.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.4
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• pp.384-391
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• 2017

Effects of operating variables on solid circulation rate were measured and discussed using two-interconnected circulating fluidized bed system at ambient temperature and pressure. OCN 706-1100 particles were used as oxygen carrier. The measured solid circulation rates increased as the lower loop seal gas flow rates and the solid height in the fuel reactor increased. Suitable operating conditions to avoid choking of the air reactor were confirmed. Continuous long-term operations of steady-state solid circulation were also demonstrated at two different conditions based on the operating window.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1178-1189
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• 2018

In grid-connected voltage-source inverters (VSIs), when compared with a simple inductive L filter, the LCL filter has a better performance in attenuating the high frequency harmonics caused by the pulse-width modulation of power switches. However, the resonance peaks generated by the filter inductors and capacitors can make a system unstable. In terms of simplicity and filter design cost, a passive damping method is generally preferred. However, its high power loss and degradation in high frequency harmonic attenuation are significant demerits. In this paper, a mathematical design solution for a passive LCL filter to derive filter parameters suppressing the high frequency current harmonics to 0.3% is proposed. The minimum filter inductance can be obtained to reduce the size of the filter. Furthermore, a minimum damping resistance design considering a current controller is analyzed for a stable closed-loop system. The proposed design method is verified by experimental results using a 5-kW three-phase prototype inverter.