• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1114-1116
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• 2003

Voltage sags are known as a serious problem causing mal-operation of equipment like computers, process controllers and adjustable-speed drives. In this paper, characterization of voltage sag and an overview of methods used in the mitigation of voltage sags are presented. Moreover a fast detection method for voltage disturbances is explored. The algorithm is based on the theory that allows a set of three-phase voltages be converted the d-q value. The utility input voltages are sensed and then converted to some quantities in the d-q transformation. And the difference between reference value and input value are showed that some disturbances happened in the system.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.213-216
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• 2003

A voltage sag is a short-duration reduction in rms voltage, and utilities have been faced with rising numbers of complaints about the quality of power due to voltage sags. In this paper, vulnerable areas of voltage sag are determined using representative loads at the buses. The CBEMA curves of the representative loads are used to determine whether the bus is vulnerable or not. Also, the ares are displayed with geographical information in order to help operators understand the situation going on easily. The proposed simulator is applied to Jeju power system to show its capabilities.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.69-73
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• 2006

The calculation of depth and duration of a sag is in both methods based on two simple assumptions. One is that due to the short circuit, the voltage drops to a low value immediately magnitude. Another is that when the fault is cleared. the voltage recovers immediately. These assumptions, however, do not hold in the case of a substantial part of the load consisting of electrical motors like in many industrial power systems. During the short circuit, the motors will slow down. Their reacceleration after the fault will increase the load current and thus prolong the voltage sag. This paper will discuss some of the aspects of the influence of induction motors on voltage sags.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2003.11a
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• pp.111-116
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• 2003

Recently, power-electronics equipments or machine that microprocessor is included and computers have been installed continuously in industrial process or region of electronics customer. So concern for power quality, especially sags has been increased. Because those equipments are very sensitive to sags. The sag is phenomenon that magnitude of load voltage temporarily decreases because of power system fault. If a certain equipment in industrial process have any trouble result from sag, it can cause utility to be charged for enormous economics loss. Therefore it need to analyze the characteristic of sag and then mitigation method for sags in distribution system in oder to increase reliability. This paper gives an overview of sags characteristic due to short circuit fault in distribution system and after a general discussion of the various forms mitigation, gives a sags mitigation method with concentrating on mitigation-device interface method, especially FCL that is Fault Current Limiter.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.05a
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• pp.80-83
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• 2009

커패시터는 전동기와 같은 유도성 부하에 필요한 무효전력을 전원측을 대신하여 공급하여 전력요금을 절감하는 역할 외 비선형부하에서 발생하는 고조파를 저감하기 위해 리액터와 함께 사용하고 있다. 전기품질은 거의 대부분이 전압품질에 관련된 것으로서 안정적인 전원공급이 매우 중요하지만, 부하의 운전상태에 따라 전압의 크기가 일시적으로 변화가 존재할 경우 커패시터와 같은 전기기기에 좋지 않은 결과를 초래할 수 있다. 본 연구에서는 일시적인 전압의 변화인 sag와 swell시 커패시터에서의 전압, 전류 및 용량의 변화를 리액터 부착전과 후의 해석결과 sag시는 문제가 되지 않지만, swell 구간에서는 커패시터에 상당한 스트레스를 줄 수 있다는 것을 확인할 수 있었다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.1
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• pp.96-104
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• 2014

The all pass filter generates a virtual q-axis voltage component with $90^{\circ}$ phase delay but the virtual q-axis voltage cannot detect the voltage depending on the phase of the grid voltage. To overcome the problem, q-axis voltage component is generated from difference between the current and previous value of d-axis voltage component in the stationary reference frame. However, the difference voltage between the current and previous value around the zero crossing voltage is not enough to detect the voltage sag. Therefore, the new detection scheme which can detect the sag around the zero crossing voltage is proposed.

• Proceedings of the KAIS Fall Conference
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• 2010.05a
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• pp.353-356
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• 2010

본 논문에서는 풍력발전 시스템이 연결된 배전계통에 고장이 발생한 경우 부하가 어떠한 특성을 보이는가를 분석하였다. 고장이 발생하면 부하전압이 감소하는 전압저하(sag)현상이 발생하는데, 특히 동적인 동작 특성을 가진 유도전동기 같은 부하인 경우에는 고정부하와 달리 고장시 뿐만 아니라 고장이 복구된 후에도 재기동에 의해 2차 전압감소가 발생하여 전동기 동작이 정지되는 등의 심각한 상황이 발생할 수 있다. 따라서 풍력발전 시스템이 연결된 전동기 부하와 연결되지 않은 전동기 부하의 전압저하 현상을 비교 분석함으로서, 신재생에너지로 크게 각광받고 있는 풍력발전시스템의 계통연계에 따른 전압 저하현상 개선 특성을 분석 검토 하였다.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1483-1485
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• 2005

In recent years, customers and power supplies are interested in power quality. Demands of customers are change from standard quality of distribution power system to various high quality of distribution power system. so, it is necessary to apply power quality compensator. in our project, we develop the UPQC(Unfied Power Quality Compensator of 45kVA which compensates power factor and voltage sag, interruption. it is very frequently occurred power quality problems. As a series and shunt compensator, UPQC consists of two inverters with common dc link capacitor bank. It compensates the current quality in the shunt part and the voltage quality in the series part. In this paper, we present simulation and test result of developed UPQC system. Test for UPQC are performed at voltage sag, flickers and non-linear load conditions. For voltage sag and ficker generation, we use RTDS(Real Time Digital Simulator) and power amplifier system.

• Proceedings of the KIEE Conference
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• 1998.11a
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• pp.282-285
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• 1998

This paper presents a method to evaluate the effect of voltage sag in distribution system using the component reliability data of utilities. The proposed method is based on Specified CBEMA curve which is the probability curve of the customers' effect by voltage sag. We carried out the experiment for the customers' sensitive equipments using the test facilities in KERI. The Monte Carlo method and the historical reliability data in KEPCO are used for simulations.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.882-884
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• 2005

A new rectangular shape microlens array having high sag for solid-state lighting is presented. Proposed microlens, which has high sag, over $375{\mu}m$ and large diameter, over 3 mm can enormously enhance output optical extraction efficiency. Rectangular shape of microlens can maximize the fill factor of light-emitting-diode (LED) package and minimize the optical loss at the same time. This wafer level microlens array is fabricated on LED package. It has many advantages in optical properties, low cost, high aligning accuracy, and mass production.