• 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.

• Journal of IKEEE
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• v.14 no.3
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• pp.236-243
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• 2010

Power quality mitigation devices play an important role in lots of industrial segments. Although there were many devices available in the market, the selection of an appropriate device specially for voltage sags and interruptions mitigation has been a challenge in the utility and customer for several years. It usually depends on technical and economic characteristics of the device. Nevertheless, most mitigation method is selected by rule of thumb or empirical method. In this paper, the life cycle cost analysis for the probabilistic risk assesment of voltage sag mitigation method is performed using either the deterministic or probabilistic approach. The difference between a deterministic and a probabilistic cost analysis approach is illustrated with five different case studies. This paper not only provides a comparison of life cycle costing of various devices but it also indirectly shows the possible savings due to the mitigation of voltage sags in the form of a project balance chart.

• Journal of Power Electronics
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• v.14 no.1
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• pp.165-174
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• 2014

The cascaded H-Bridge Dynamic Voltage Restorer (DVR) is used for protecting high voltage and large capacity loads from voltage sags. The LC filter in the DVR is needed to eliminate switching ripples, which also provides an accurate tracking feature in a certain frequency range. Therefore, the parameter optimization of the LC filter is especially important. In this paper, the value range functions for the inductance and capacitance in LC filters are discussed. Then, parameter variations under different conditions of voltage sags and power factors are analyzed. In addition, an optimized design method is also proposed with the consideration of multiple impact factors. A detailed optimization procedure is presented, and its validity is demonstrated by simulation and experimental results. Both results show that the proposed method can improve the LC filter design for a cascaded H-Bridge DVR and enhance the performance of the whole system.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.62 no.4
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• pp.210-215
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• 2013

This paper analyze the bus voltage sags in the power distribution system with a small scale cogeneration system when the superconducting fault current limiter was introduced. Among the solutions to decrease the short-circuit current considering the locations of the small scale cogeneration system, the superconducting fault current limiter (SFCL) has been announced as one of the promising methods to reduce the fault current because the installation of the small scale cogeneration system which increases the short-circuit current. According to the application locations of the small scale cogeneration system in a power distribution system, it has caused the variations of voltage sag and duration which depends on the change of the short-circuit current, which can make the operation of the protective device deviate from its original set value when the fault occurs. To investigate the voltage sag when a SFCL was applied into a power distribution system where the small scale cogeneration system was introduced into various locations, the SFCL, small scale cogeneration system, and power system are modeled using PSCAD/EMTDC. In this paper, the effects on voltage sags are assessed when the SFCL is installed in power distribution system with various locations of the small scale cogeneration system.

• KIEE International Transactions on Power Engineering
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• v.5A no.2
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• pp.97-102
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• 2005

Voltage sags are the most widespread quality issues affecting distribution systems. This paper describes in some detail the voltage sag characteristics due to different types and locations of fault in a practical low voltage power distribution system encountered in the UK. The results not only give utility engineers very useful information when identifying parts of the system most likely to pose problems for customer equipments, but also assist the facility personnel to make decisions on purchasing power quality mitigation equipment.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.12
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• pp.705-712
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• 2003

In this paper, we propose new unified methodologies of reliability and its cost evaluation in power distribution systems. The unified method means that the proposed reliability approaches consider both conventional evaluation factor, i.e. sustained interruptions and additional ones, i.e. momentary interruptions and voltage sags. Because the three voltage quality phenomena generally originate from the outages on distribution systems, the basic and additional reliability indices are summarized considering the fault clearing mechanism. The proposed unified method is divided into the reliability evaluation for calculating the reliability indices and reliability cost evaluation for assessing the damage of customer. The analytic and probabilistic methodologies are presented for each unified reliability and its cost evaluation. The time sequential Monte Carlo technique is used for the probabilistic method. The proposed DVL(Demand Varying Load) model is added to the reliability cost evaluation substituting the average load model. The proposed methods are tested using the modified RBTS(Roy Billinton Test System) form and historical reliability data of KEPCO(Korea Electric Power Corporation) system. The daily load profile of the each customer type in domestic are gathered for the DVL model. Through the case studies, it is verified that the proposed methods can be effectively applied to the distribution systems for more detail reliability assessment than conventional approaches.

• 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 Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.427-430
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• 2001

Computers and automated manufacturing processes in industry are very susceptible to voltage sags and surges. The need for greater power reliability makes the end-users to use the uninterruptible power supply and other electronic power conditioning means to maintain the stable voltage. In this paper, a single-phase buck ac-ac converter for Custom Power Applications is presented. The presented converter uses IGBT's as switching module and maintains the stable voltage through PWM technology in spite of the input voltage sags and load rejections. In this paper, the operation characteristics of the power converter at steady state are illustrated using PSPICE simulations.

• Proceedings of the KIEE Conference
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• 2002.11c
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• pp.286-289
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• 2002

In this paper, we use the PI dual control using do transformation(dq stationary frame and dq synchronous rotating frame) for series voltage sag and swell compensation algorithm. Analysis, simulation results are presented for voltage sags and swells on a three-phase unbalanced voltage source.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.10
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• pp.1271-1277
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• 2018

This paper deals with a voltage sag assessment based on a voltage monitoring program. The voltage sag performance at a specific site can be evaluated by analyzing voltage monitoring data recorded for a long time period. Although an assessment based on voltage monitoring is an effective way to understand voltage sag performance at a measurement site, the statistical confidence of voltage sag frequency estimation heavily depends on the length of monitoring period and the number of recorded events. Short monitoring period and insufficient recorded data can not provide a reliable assessment result. This paper proposes a compensation assessment method by combining a computer simulation approach for in case that monitoring period and data are not enough for a valid assessment.