• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.30 no.2
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• pp.85-92
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• 2016

The paper presents a method to assess system voltage sag performance considering sag durations as well as magnitudes. In general, voltage sag assessment for large power systems is performed only considering sag magnitudes at sensitive load points. However some equipment can be affected by certain sag durations. The duration of the voltage sag is depend on the time of fault current flow in the system. Therefore, the duration can be determined by analyzing the operating characteristic of the protection system. In this paper, an effective method to evaluate sag durations regarding the characteristics and failure rates of the protection system is described. The proposed method can be used to assess the long-term performance of the voltage sags in large power system.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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• pp.37-40
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• 2008

This paper presents the results of a simulation to analyze the effects of voltage sag on high-pressure discharge lamp(400[W]). In this paper, voltage sag is considered a reduction between 0 and 0.9[p.u] in nominal voltage magnitude, with duration between 0.01 and 90cycle. The simulation results depict the characteristics of the lamp about operating limits during voltage sag by the magnitude and duration of sag in CBEMA curve.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.304-306
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• 2002

This paper presents a new method to characterize sag event. Power quality monitoring algorithm to analyze PQ problems is described. This paper shows that conventional characterizing method which makes use of only sag magnitude and sag duration has some limitations. It characterizes non-rectangular sag as more severe one. In addition, it can't count on voltage tolerance characteristics of each apparatus. In order to solve these problems, this paper present a new characterizing method and it properly characterizes non-rectangular sag considering the voltage tolerance characteristics.

• Journal of Power Electronics
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• v.11 no.6
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• pp.897-903
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• 2011

Many voltage sag compensators have been introduced, including the traditional dynamic voltage restorer (DVR), which requires an energy storage device but is inadequate for compensating deep and long-duration voltage sags. The AC-AC sag compensators introduced next do not require a storage device and they are capable of compensating voltage sags. This type of compensator needs an AC-AC converter to regulate the output voltage. Presented in this paper is a three-phase PWM-switched autotransformer voltage sag compensator based on an AC-AC converter that uses a proposed detection technique and PWM voltage control as a controller. Its effectiveness and capability in instantly detecting and compensating voltage sags were verified via MATLAB/Simulink simulations and further investigated through a laboratory prototype developed with a TMS320F2812 DSP as the main controller.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.307-309
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• 2005

This paper studies the effects caused by symmetrical and unsymmetrical voltage sags on three-phase transformer and induction machine. The voltage sag on transformer and induction machine gives rise to inrush current. This inrush current makes sag more severe. These effects depend or many elements such as sag magnitude and duration, type of sag, and fault and recovery voltage instants.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.1
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• pp.29-34
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• 2015

This paper presents a method to select optimal device for mitigating voltage sags. The method is based on economic evaluation and voltage sag assessment involving sag duration as well as magnitude. The economic evaluation is performed by using the operation cost and economic benefit of the mitigation devices. The optimal device can be determined from the values of NPV (net present value) which is widely accepted in cost-benefit analysis. The proposed method can help sensitive customers to select optimal mitigation device. In this paper, the case study considering two sensitive customers was performed by using the proposed method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.3
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• pp.336-343
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• 2008

In this study, a transition of power quality was characterized by non-linear voltage electric equipments under voltage sag. The test was inputted voltage sag to IPC(Sag Generator) from AVR, and then to equipments by IPC which adjust voltage magnitude and duration. The load test which non-linear voltage electric equipments used PLC, Magnetic Contactor, SMPS, HID Lamp. The test result was different from each other according to a manufacturing companys, models, and equipments. PLC was greatly described to be stabilized voltage sag in case of no load then rated load. Magnetic Contactor was made a difference to phase angles on voltage sag, which was $0^{\circ}$, $30^{\circ}$, $60^{\circ}$, $90^{\circ}$. HPD Lamp was described to be stabilized the sodium lamp, and to be unstabilized the metal hailed lamp. The test result was showed CBEMA curve that stand for evaluated responsiveness of voltage sag. This study was tested description to dynamic characteristics on non-linear voltage electric equipment under voltage sag. There was hoped that power system designed the essential particulars.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.1
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• pp.15-22
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• 2001

In this paper, a VSC(Voltage Sag Corrector) is discussed for the purpose of power quality enhancement. A fast detecting technique of voltage sag is accomplished through the detection of instantaneous value on synchronous reference frame. A robust characteristic against the noise is available by inserting the first order low pass filter in the detection circuit. The formula and the filter design process is described properly with the mathematical equations. Because the VSC system supply the active power to load, it is required to design the proper size of the energy storage system, In this paper, the capacitor bank is used as an energy storage system, and the size of the capacitor is designed from the point of view of input/output energy as the output power rating and the amplitude and duration time of the voltage sag. The simulation is accomplished by PSCAD/EMTDC.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.49 no.9
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• pp.425-432
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• 2000

Wavelet transform is a new method fro electric power quality analysis. Several types of mother wavelets are compared using voltage sag data. Investigations on the use of some mother wavelets, namely Daubechies, Symlets, Coiflets, Biorthogonal, are carried out. On the basis of extensive investigations, optimal mother wavelets for the detection of voltage sag are chosen. The recommended mother wavelet is 'Daubechies 4(db4)' wavelet. 'db4', the most commonly applied mother wavelet in the power quality analysis, can be used most properly in disturbance phenomena which occurs rapidly for a short time. This paper presents a discrete wavelet transform approach for determining the beginning time and end time of voltage sags. The technique is based on utilising the maximum value of d1(at scale 1) coefficients in multiresolution analysis(MRA) based on the discrete wavelet transform. The procedure is fully described, and the results are compared with other methods for determining voltage sag duration, such as the RMS voltage and STFT(Short-Time Fourier Transform) methods. As a result, the voltage sag detection using wavelet transform appears to be a reliable method for detecting and measuring voltage sags in power quality disturbance analysis.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.49 no.4
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• pp.177-184
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• 2000

In this paper, we proposes a method for assessing the effect of voltage sag in power distribution systems using fuzzy model. The proposed method is based on the reliability data of distribution system and specified computer business equipment manufacturer association(SCBEMA) curve that express the representative power acceptability curve by voltage sag for each customer type. The SCBEMA curves are made by using the CBEMA curves obtained from the experiment for the customers sensitive equipment. In order to transform SCBEMA curves to the differential damage by voltage sag, a fuzzy model is used. The proposed fuzzy model is composed to reflect two parameters of customers damage by voltage sag. One is the duration and magnitude of voltage sag and the other is the different risk due to the customer types. The Monte Carlo simulation method and the historical reliability data in KEPCO ae used for case studies.