• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.12
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• pp.93-98
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• 2012

Economics of available alternatives in the transmission planning are evaluated by the investment cost, loss cost and congestion cost. Congestion/loss cost is calculated in many years and many load levels by unit commitment of generators, optimal dispatch, load flow, judgement about transmission congestion and re-dispatch to reduce the congestion. The greatest difficulties to introduce variable optimization techniques on the transmission planning is the convergence of load flow. In this paper, economics in the transmission planning are evaluated using DC load flow, and case study is conducted on the Korea power system by proposed congestion/loss calculation methods.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.3
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• pp.131-137
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• 2014

It is expected that there will be delay of scheduled transmission network reinforcement and huge investment of renewable energy resources in Korea. As transmission capacity expansion delayed, supplying power to Seoul metropolitan area will not be increased as scheduled. In addition, uncertain renewable energy out of Seoul metropolitan area can cause transmission congestion in the future power system. These two combining effects will make the difference in locational marginal prices(LMP) and congestion costs increase. In that sense, this paper will analyze how much the congestion costs for Korea power system are incurred in the future power system. Most of previous approaches to analyze the congestion costs for electric power system are based on the optimal power flow model which cannot deal with hourly variation of power system. However, this study attempted to perform the analysis using market simulation model(M-Core) which has the capability of analyzing the hourly power generation cost and power transmission capacity, and market prices by region. As a result, we can estimate the congestion costs of future power system considering the uncertainty of renewable energy and transmission capacity.

• Journal of Electrical Engineering and Technology
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• v.6 no.3
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• pp.302-310
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• 2011

Congestion management is one of the most challenging tasks of a system operator to ensure the operation of transmission system within operating limits. In this paper, cluster/zone method and relative electrical distance (RED) method for congestion management are compared based on the considered parameters. In the cluster/zone method, rescheduling of generation is based on user impact on congestion through the use of transmission congestion distribution factors. In the RED method, the desired proportions of generations for the desired overload relieving are obtained. Even after generation rescheduling, if congestion exists, load curtailment option is also introduced. Rescheduling cost, system cost, losses, and voltage stability parameter are also calculated and compared for the above two methods of congestion management. The results are illustrated on sample 6-bus, IEEE 30-bus, and Indian utility 69-bus systems.

• KIEE International Transactions on Power Engineering
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• v.11A no.4
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• pp.21-26
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• 2001

As competition is introduced in the electricity supply industry, congestion becomes a more important issue. Congestion in a transmission network occurs due to an operating condition that causes limit violations on the transmission capacities. Congestion leads to inefficient use of the system, or causes additional costs (Congestion cost). One way to reduce this inefficiency or congestion cost is to control the transmission flow through the installation of UPFC (Unified Power Flow Controller). This paper also deals with an optimal siting of the UPFC for reducing congestion cost by using shadow prices. A performance index for an optimal siting is defined as a combination of line flow sensitivities and shadow prices. The proposed algorithm is applied to the sample system with a condition, which is concerning the quadratic cost functions. Test results show that the siting of the UPFC is optimal to minimize the congestion cost by the proposed algorithm.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.22-24
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• 2000

As a competition is introduced in the electricity supply industry, a congestion problem arises in the transmission network. The congestion causes the transmission cost to increase. One way to decrease the congestion cost is to control the transmission flow through the installation of FACTS(Flexible AC Transmission system). This paper deals with the optimal site of the FACTS for reducing the congestion cost using a shadow price which is one of the economic signals for the systems. Test results show that the site of the FACTS(UPFC) is optimal to minimize the congestion cost by the proposed algorithm.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.430-431
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• 2011

Recently the power system consists of the more complicated structure, due to increase of power demands. In this circumstance, the congestion and loss capacity in transmission line is also increased. Accordingly, the investment planning of transmission system is required to reduce the congestion and loss of the transmission line. In study of the planning of domestic and international transmission expansion, the reliability of transmission planning and minimizing Investment cost is focused. However, the study has not been performed systematically in economic aspects. Typically, the congestion and loss costs have been individually calculated. It is not consider the mutual relationship between the congestion cost and the loss cost. This paper proposes a method to compute concurrently the congestion and loss costs. This purpose is to calculate the more exact value for economic assessment of the power system operation.

• Journal of Digital Contents Society
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• v.16 no.3
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• pp.381-388
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• 2015

TCP, which performs congestion control in congestion condition, is able to help a reliable transmission. However, packet loss can be increased because congestion window is increased by the time the packet is dropped in the process of congestion avoidance. In this paper, to solve the above problem, we propose a new congestion estimation based TCP congestion control scheme using the weighted average value of the RTT. After measuring a SRTT, which means the weighted average value of RTTs, at this point of time when a buffer overflow is occurred by an overloaded packet, the proposed scheme estimates the time, when the same SRTT is made in packet transmission, as a congestion time and then decreases the congestion window. The simulation results show that the proposed schem has a good performance in terms of packet loss rate and throughput when the packet loss due to buffer overflow is larger than that due to wireless channel.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.3
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• pp.285-289
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• 2004

Recently, due to the high development of the internet, needs for multimedia streams such as digital audio and video is increasing much more. In case of transmitting multimedia streams using the User Datagram Protocol (UDP), it may cause starvation of TCP traffic on the same transmission path, thus resulting in congestion collapse and enormous delay because UDP does not perform TCP-like congestion control. Because of this problem, diverse researches are being conducted on new transmission schemes and protocols intended to efficiently reduce the transmission delay of real-time multimedia streams and perform congestion control. The TCP-friendly congestion control schemes can be classified into the window-based congestion control, which uses the general congestion window management function, and the rate-based congestion control, which dynamically adjusts transmission rate by using TCP modeling equations and the like. In this paper, we suggest the square-root congestion avoidance algorithm with the hybrid TCP-friendly congestion control scheme which the window-based and rate-based congestion controls are dealt with in a combined way. We apply the proposed algorithm to the existing TEAR. We simulate the performance of the proposed TEAR by using NS, and the result shows that it gives better improvement in the stability needed for providing congestion control than the existing TEAR.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.49 no.5
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• pp.220-225
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• 2000

As a competition is introduced in the electricity supply industry, a congestion problem arises in the transmission network. The congestion causes the transmission cost to increase. One way to decrease the congestion cost is to control the transmission flow through the installation of TCSC(Thyrister Controlled Series Capacitor). This paper deals with the optimal site of the TCSC for reducing the congestion cost using a shadow price which is one of the economic signals for the systems. Test results show that the site of the TCSC is optimal to minimize the congestion cost by the proposed algorithm.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.4
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• pp.560-566
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• 2008

Today, as the power trades between generation companies and power customer are liberalized, the uncertainty level of operated power system is rapidly increased. Therefore, transmission operators as decision makers for transmission expansion are required to establish a deliberate investment plan for effective operations of transmission facilities considering forecasted conditions of power system. This paper proposes the methodology for the optimal solution of transmission expansion in deregulated power system. The paper obtains the expected value of transmission congestion cost for various scenarios by using occurrence probability. In addition, the paper assumes that increasing rates of loads are the probability distribution and indicates the location of expanded transmission line, the time for transmission expansion with the minimum cost for the future by performing the Montecarlo simulation. To minimize the investment risk as the variance of the congestion cost, Mean-Variance Markowitz portfolio theory is applied to the optimization model by the penalty factor of the variance. By the case study, the optimal solution for transmission expansion plan considering the feature of market participants is obtained.