• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.1
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• pp.37-44
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• 2006

In this paper we explore the susceptibility of common sensitive loads by voltage sags of power distribution systems. The experimental approach was used for obtaining the susceptibility of single-phase loads and the three-phase induction motor. The experimental result of single-phase loads was transformed to the ITIC(Information of Technology Industry Council) format and used for evaluating the adverse impacts of a individual and repetitive sags using the performance contour of the foreign standard data. In order to assess the impact of voltage sags on three-phase induction motor, also, the experiment was peformed. The experiment was focused on the current, torque, and speed loss of the motor during a voltage sag. For comparing the impacts of individual and repetitive voltage sags, the variations of motor torque is focused among the experimental results. The sensitive curves of instantaneous current peak are used to describe the susceptibility of three-phase induction motor and 진so it were used for the quantitative analysis of the impact of three-phase induction motor due to voltage sags. Through the results of experiment, we verified that some types loads have more severe impact at repetitive voltage sags than individual ones and proposed method can be effectively used to evaluate the actual impact of voltage sags.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2002.11a
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• pp.139-145
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• 2002

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 odor 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 changing the distribution system like spot network, on-site generation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.6
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• pp.1034-1040
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• 2010

This paper presents a calculation method of the area of severity for the stochastic assessment of voltage sags. In general, the annual expected numbers of voltage sags at an individual load point can be estimated stochastically. However, in order to assess the system voltage sag performance considering many sensitive load points together, it is necessary to determine and analysis the area of severity for the load points. The area of severity to voltage sags is the network region where the fault occurrences will simultaneously lead to voltage sags at different load points. In this paper, the concept of the voltage sag assessment and the calculation method of the area of severity are addressed. The analysis of the area of severity is performed on the IEEE 30-bus test system by using the proposed method. The method is useful for the stochastic assesment of voltage sags and the establishment of systematic plans for voltage sag mitigation.

• 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.

• KIEE International Transactions on Power Engineering
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• v.5A no.3
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• pp.293-299
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• 2005

Automatic reclosing is a typical protection method in power distribution systems for the clearing of temporary faults. However, it has a fatal weakness in regards to voltage sags because it produces repetitive voltage sags. In this paper, we explored the repetitive impact of voltage sag due to the automatic reclosing of power distribution systems. The actual tests of low voltage loads were carried out for obtaining the susceptibility of voltage sags. The final results of the tests yielded power acceptability curves of voltage sag, and the curves transformed the 3-dimensional CBEMA (Computer Business Equipment Manufacturer Association) format. For the quantitative evaluation of the impact of repetitive voltage sags, an assessment formulation using the voltage sag contour was proposed. The proposed formulation was tested by using the voltage sag contour data of IEEE standard and the results of the test. Through the case studies, we verified that the proposed method can be effectively used to evaluate the actual impact of repetitive voltage sags.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.5
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• pp.13-20
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• 2008

Power quality problems such as momentary interruptions and voltage sags do not great influence on loads at past. However, the interests in power quality problems increase as the use of sensitive loads with microprocessor like computers increases recently. Accordingly, power system reliability research focusing to sustained interruption and momentary interruption partially needs more accurate evaluation methods including momentary and instantaneous problems. That is, many sensitive loads being tripped by voltage sags result in interruption costs. In this paper, new reliability worth evaluation method is presented considering voltage sags. We calculated the magnitude of voltage sags using fault studies and the duration of voltage sags using the trip time of protective relays for each fault. Moreover, we includes the customer interruption cost resulted from sensitive load trip by voltage sags. Through case studies, we evaluate the effects of voltage sags for permanent faults.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.324-325
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• 2011

This paper addresses the assessment of voltage sag costs based on the stochastic prediction of voltage sags. When voltage sags below a certain voltage threshold occur at sensitive industrial process, the industrial customer will experience financial damage. In order to mitigate voltage sag costs and devise efficient solutions to mitigate damage, a study on the financial loss assessment of voltage sags is basically needed. In order to assess the voltage sag costs, the expected sag frequency at a sensitive load point should be calculated by using the concept of the area of vulnerability and historical fault statistics. Then, financial loss due to voltage sags can be obtained by multiplying the expected sag frequency by the cost per sag event.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.6
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• pp.315-322
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• 2005

In this article, 1 would like to explore the estimation method of time-varying voltage sags in large industrial systems considering the short circuit contributions of rotating machines. For the power distribution system of KEPCO(Korea Electric Power Corporation), the magnitude of initial symmetrical short circuit current is generally not changed. However, in industrial systems which contain a number of rotating machines, the magnitude of voltage sag is generally changed from the initial to the clearing time of a fault due to the decreasing contribution of rotating machines for a fault current. The time-varying characteristics of voltage sags can be calculated using a short circuit analysis that is considered the time-varying fault currents. For this, the prediction formulations of time-varying voltage sags are proposed using a foreign standard. The proposed method contains the consideration of generator and motor effects. For the test of proposed formulations, a simple system of industrial consumer is used for the comparison conventional and proposed estimation method of voltage sag characteristics.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.11
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• pp.1611-1617
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• 2015

This paper presents an effective approach for establishing countermeasures against voltage sags based on the concept of area of severity. In order to apply preventive measures against faults such as lightning arrester, overhead earth wires and so on, it is important to find optimal points for installing the preventive measures. The optimal points can be determined by the calculation of the area of severity(AOS) to voltage sags and the expected sag frequency per unit length of line. In this paper, an effective method to find optimal points to apply countermeasures against voltage sags is addressed with case studies.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.12
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• pp.678-684
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• 2004

Automatic reclosing is a typical protection method in power distribution systems for clearing the temporary faults. However, it has a fatal weakness in regards to voltage sags because it produces successive voltage sags. In this paper, we explored successive impact of voltage sag due to the automatic reclosing of power distribution systems. The actual tests of low voltage loads were accomplished for obtaining the susceptibility of voltage sags. The final results of the test yielded power acceptability curves of voltage sag, and the curves were transformed the 3-dimensional CBEMA(Computer Business Equipment Manufacturer Association) format. For the quantitative evaluation of the impact of successive voltage sags, an assessment formulation using the voltage sag contour was proposed. The proposed formulation was tested by using the voltage sag contour data of IEEE standard and the results of the test. Through the case studies, we verified that the proposed method can be effectively used to evaluate the actual impact of successive voltage sans.