• Journal of Power Electronics
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• v.7 no.1
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• pp.72-80
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• 2007

Voltage sags are one of the most frequently occurring power quality problems challenging power systems today. The Unified Power Quality Conditioner (UPQC) is one of the major custom power solutions that are capable of mitigating the effect of supply voltage sags at the load or Point of Common Coupling (PCC). A UPQC-Q employs a control method in which the series compensator injects a voltage that leads the supply current by $90^{\circ}C$ so that the series compensator at steady state consumes no active power. However, the UPQC-Q has the disadvantage that its series compensator needs to be overrated. Thus it cannot offer effective compensation. This paper proposes a new control scheme for the UPQC-Q that offers minimum power injection. The proposed minimum power injection method takes into consideration the limits on the rated voltage capacity of the series compensator and its control scheme. The validity of the proposed control scheme is investigated through simulation and experimental results.

• Proceedings of the KIEE Conference
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• 2002.11b
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• pp.202-205
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• 2002

This paper presents the reliability evaluation methods considering the momentary voltage quality in power distribution systems. The voltage qualify phenomena deal with this paper are sustained and momentary interruptions and voltage sags. Conventional evaluation indices and methods are summarized for the sustained interruptions, and the assessment methodologies of momentary interruptions and voltage sags are proposed. The evaluation methods are divided into the analytical method and Time Sequential Monte Carlo simulation. The proposed methods are tested using the modified RBTS (Roy Billinton Test System) form and historical reliability data of KEPCO system.

• Proceedings of the KIEE Conference
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• 2002.04a
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• pp.116-118
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• 2002

Of all known power quality problems, voltage sags provide the largest reason for concern. Sags occurs more frequently than outages and therefore tend to be more costly for industry as modern technical equipment becomes all the more sensitive to the quality and reliability of supply. Therefore we designed for a new model for Voltage Sag compensator, and we will implement Anti-Windup PI Controller with IP Block.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.6
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• pp.746-751
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• 2014

This paper presents a method to calculate a sag cumulative table and density table based on the area of vulnerability to voltage sags. The expected sag performance at sensitive load points can be easily assessed through the calculation of the sag cumulative table and density table. However, the calculation of the tables regarding large power systems is very difficult task. Therefore, an efficient method for calculating the tables is needed. In this paper, the improved method to determine the areas of vulnerability is addressed and the method to calculate the tables based on the area of vulnerability is also described. The proposed scheme can be efficiently used to assess the voltage sag performance at sensitive load points in large power systems.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.128-130
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• 2003

In recent years, both utilities and users have expressed their deep concerns about the quality of electric power. Expressed, voltage sag which is one of power quality disturbance is very serious power quality problem on the power system. Voltage sag is a decrease to between 0.1 and 0.9 pu in rms voltage magnitude on the power system for durations from 0.5 cycles to 1 minute. These voltage sags are usually caused by fault condition, overload, and starting of large motors. In this paper, different types of voltage sags are simulated by using EMTP. This paper describes the distinctive characteristic for various sag origins, proposes the effective technique for voltage sag detection using EMTP.

• Animal cells and systems
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• v.9 no.3
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• pp.127-133
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• 2005

We investigated expression of cucumber senescence-associated genes (SAGs) from developing cotyledons and flower petals. Several cucumber SAGs have been reported in earlier reports. This is an extension of the previous findings. Semi-quantitative RT-PCR revealed that most of the cucumber SAG transcripts were consistently produced until the organ senescence. These results imply that many cucumber senescence-related genes are still active during the final development stage, playing some executive biological roles, possibly in remobilization of nutrients to the other parts of tissues or organs. These results were used to search for possible functions of senescence-related genes during organ development.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.7
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• pp.1293-1298
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• 2011

This paper presents an Unified Index which can evaluate a performance of a distribution system based on value-based methodology. Reliability cost and voltage sags cost are calculated for each load point using Reliability Sector Customer Damage Function(SCDF). Aging cost is calculated for each load point using Aging SCDF. Power loss cost and operation cost are calculated for the system. By summation of each cost of load point and system, power quality cost can be obtained. Finally, this paper developed an unified index which can show the performance of a distribution system. Presented method has been applied to a real system, the usefulness of the method has been verified.

• 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 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 KIEE Conference
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• 2007.07a
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• pp.1099-1101
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• 2007

In this paper, a study has been performed for development of dynamic voltage restorer(DVR) system using EDLC (Electric Double Layer Capacitor) to solve voltage sags which are considered the dominant disturbances affecting power quality. With the prolific use of semiconductor devices in electrical equipment, modern-day loads are becoming increasingly sensitive to the sags and the disturbances prove to be costly to industries. As a technology-driven custom power installation, the Dynamic Voltage Restorer (DVR) is recognized to be most effective equipment that can be used to counter the voltage sag problem. Hence, this paper proposes the high-performance optimal design of On-Line type DVR system which can efficiently compensate the instantaneous voltage sag and instantaneous interruption of the utility voltage source.