• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.1
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• pp.1-7
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• 1999

In power transformers, vibration signals can occur at winding and core due to the change of current, voltage, and temperature and the deformation of winding and core. The deformation of winding and core occurs electromagnetic force induced by fault current in power systems. There firem the changes of vibration signals can be very different in normal or fault states of power transformers. We edtect and analyze the changes of vibration signals and use them as a tool for fault diagnosis of power transformers. This paper presents fault discriminating polliblility using the changes of fundamental waves and higher harmonics in power transformers. We showed the fault discriminating functions that are made at each case ; normal state and fault state. These functions are tested by the detected vibration signals, and we showed that the proposed method can discriminate the state of power transformers.

• Journal of the Earthquake Engineering Society of Korea
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• v.25 no.5
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• pp.201-211
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• 2021

The Ministry of the Interior and Safety in Korea developed seismic fragility function for various building types in 2009. Damage states for most building types were determined by structural analyses of sample models and foreign references because actual cases damaged by earthquakes rarely exist in Korea. Low-rise, piloti-type buildings showed severe damage by brittle failure in columns due to insufficient stirrup details in the 2017 Pohang earthquake. Therefore, it is necessary to improve damage state criteria for piloti-type buildings by consulting actual outcomes from the earthquake. An analytical approach was conducted by developing analysis models of sample buildings reflecting insufficient stirrup details of columns to accomplish the purpose. The result showed that current spectral displacements of damage states for piloti-type buildings might be too large to estimate actual fragility. When the brittle behavior observed in the earthquake is reflected in the analysis model, one-fourth through one-sixth of current spectral displacements of damage states may be appropriate for existing low-rise, piloti-type buildings.

• The Journal of the Korea institute of electronic communication sciences
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• v.19 no.5
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• pp.861-866
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• 2024

The operation mechanism of the superconducting coupled DC circuit breaker system and the simulation analysis of the transient state in DC power networks showed that, when only a conventional DC circuit breaker was applied, the fault current increased and the interruption operation was not fully achieved. In contrast, when coupled with superconductors, the fault current was limited, and the interruption operation was completed quickly. The superconducting coupled DC circuit breaker system proposed in this paper is stable and has the potential to respond to increases in the capacity of power systems. Additionally, it has been confirmed that this system can reduce the burden on circuit breakers, thereby enhancing their lifespan and stability.

• Proceedings of the KIPE Conference
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• 2008.10a
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• pp.124-126
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• 2008

Grid Connected inverter is produced current to deliver power to grid. To provide low THD current, LCL filters is effective to filter high frequency component of current output from inverter. To provide sinusoidal waveform, there are many researchers have been proposed several controllers for grid-connected inverter controllers. Synchronous Reference Frame (SRF)-based controller is the most popular methods. SRF-based controller is capable for reducing both of zero-steady state error and phase delay. But SRF based controller is contained cross-coupling components, which generate some difficulties to analyze. In this paper, SRF based controller is analyzed. By applying decoupling control, cross-coupling component is eliminated and single phase model of the system is obtained. Through this single phase model, gain controller is designed. To reduce steady state error, proportional gain is set as high as possible, but it may produce instability. To compromise between a minimum steady state error and stability, the single phase model is evaluate through Root Locus and Bode diagram. PSIM simulation is used to verify the analysis.

• Journal of Power Electronics
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• v.18 no.6
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• pp.1830-1843
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• 2018

In this paper, the generation of a reference current and voltage signal based on a Kalman filter is offered for a 3-phase 4wire UPQC (Unified Power Quality Conditioner). The performance of the UPQC is improved with source voltages that are distorted due to harmonic components. Despite harmonic and frequency variations, the Kalman filter is capable enough to determine the amplitude and the phase angle of load currents and source voltages. The calculation of the first state is sufficient to identify the fundamental components of the current, voltage and angle. Therefore, the Kalman state estimator is fast and simple. A Kalman based control strategy is proposed and implemented for a UPQC in a distribution system. The performance of the proposed control strategy is assessed for all possible source conditions with varying nonlinear and linear loads. The functioning of the proposed control algorithm with a UPQC is scrutinized and validated through simulations employing MATLAB/Simulink software. Using a FPGA SPATRAN 3A DSP board, the proposed algorithm is developed and implemented. A small-scale laboratory prototype is built to verify the simulation results. The stated control scheme for the UPQC reduces the following issues, voltage sags, voltage swells, harmonic distortions (voltage and current), unbalanced supply voltage and unbalanced power factor under dynamic and steady-state operating conditions.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.622-624
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• 2002

This paper describes a method for steady state hot gas flow analysis considering nozzle ablation for the nozzle of $SF_6$ gas circuit breaker. In order to take account of the effect of ablated nozzle material on the hot gas flow. the PTFE mass concentration equation is added to the established equations for hot gas flow analysis. The steady state simulations were carried out under the condition of DC current flows and the results are presented.

• Journal of the Korean Society of Safety
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• v.32 no.2
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• pp.27-33
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• 2017

This study is intended to identify issues on the basis of investigating the actual state of laboratory environment and outlet circuit, and derive end states by expressing sequences from the initiating event of disaster to accident in leakage current, poor contact and overload through ETA(event tree analysis). To this end, this study investigated the actual state of electric equipment of laboratory at universities in all parts of country. And it is shown that most of them are failure in electric work and user negligence in the investigation of actual state. It is found that there is earth fault and defect in wire diameter in the failure of electric work and the problem of partial disconnection due to wire bundling and poor contact in user negligence. Outlet-related component, failure rate and initiating events are composed of a total of 41 initiating events, i.e., 30 internal initiating events and 11 external initiating events. And end states are composed of a total of 15 parts, i.e., 3 electric power parts and 12 safety parts. Earthing class 3 is the most important safety device against leakage current (initiating event). And in case of poor contact, it is necessary for manager to check thoroughly because there is no safety device. In case of overload/overcurrent, when high-capacity equipment is connected, a molded case circuit breaker, safety device, worked. However, in most cases, it is verified that this doesn't work. This study can be utilized as electric equipment safety guide for laboratory safety manager and managers.

• The Journal of the Korea Contents Association
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• v.7 no.12
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• pp.83-94
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• 2007

The portfolio can be used as a methodology supporting the learning of constructivism. Recently, the use of portfolios has been increased gradually in the education field, but a study on the current state analysis and design direction of portfolios leaves much to be desired. In this paper, we analyze statistical data on the portfolio application of teachers in domestic elementary, middle, and high school. We also propose a design direction of e-portfolio needed in the society of knowledge information based on this analysis. The results of research show that the following problems will be improved: understanding portfolio, analyzing the current state according to the types of portfolio application, designing a distinguished system according to the level of school, expanding education of teachers with high career, and developing a guide helper. The design of total system that combines the learning and evaluation is needed to improve a problem that spends lots of time to make portfolio, and operates temporally and formally achievement evaluation. In addition, the design of e-portfolio supporting efficiently interaction and self-directed teaming is required.

• Journal of the Korean Society of Clothing and Textiles
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• v.35 no.9
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• pp.1049-1059
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• 2011

This study investigates the current state of companies that manufacture and sell outdoor wear. A survey was conducted to identify what problems they had and what aspects they needed to supplement through a comparison and analysis of their block patterns. Companies that manufactured outdoor wear and those that sold them were separately surveyed to understand their current state. The manufactures included 4 companies and 14 sellers. The survey used interviews to cover the areas of target consumers, development patterns, production lines, body size, nominal size, production size, and functional materials for each item, and aspects that need improvement. The survey period was from September $3^{rd}$ to $10^{th}$ 2008. There were three block patterns for jackets, T-shirts, and pants. The investigator collected the patterns used by three outdoor clothing manu-facturers for comparison and assessment. As a result, the mean age of the target consumers set by the outdoor clothing manufacturers and sellers was 25.3-50.7 and 29.2-42.5, respectively, which shows that the outdoor clothing had a wider distribution of target consumers than the sellers. It is imperative for them to segment and differentiate the target consumers and concepts. The basic body measurements the companies used to draw the upper and lower garment patterns were the bust circumference for the upper garment patterns and the waist circumference for the lower garment patterns. The basic nominal size was 95 for the upper garment and 70 for the lower garment. Also analyzed were the block patterns according to the items to understand the pattern characteristics of each of the companies. There were a total of 35, 36, and 30 items for the jackets, T-shirts, and pants, respectively, to measure size. The items were then compared with one another in mean and standard deviation. The analysis indicate that the block patterns were not fit for women in their twenties or thirties to wear and required revisions in the length of the upper garment, the height of sleeve cap, bust circumference, hip length, and pant length.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.1
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• pp.13-21
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• 2004

In the design of superconducting cable systems, quench analysis have to be advanced for applying to a real systems. It is necessary to calculate the current, voltage and resistance during the quench. Simulation program named EMTDC was used to analyze the quench state. Normal zone evaluation and quench development with EMTDC are one of the major features of quench analysis. This paper presents the two kinds of quench control models which are the Switch Control Type and the Fortran Control Type. In case of the quench developing area, the simplicity cable model consist of resistance, inductance and capacitance. The impedance of the pipe type superconducting cable is calculated by numerical analysis method. The resistance and inductance increased during quench. However the variation have an effect on the fault current. The voltage was also developed by resistance and inductance. This paper presents the relationship between the current. voltage, resistance and inductance during quench.