Jung-Uk Lim

An analytical approach for transaction costs allocation in transmission system

This paper proposes an analytical approach for allocating transmission transaction costs among users in transmission services. The proposed method allocates the transaction costs over the participants proportional to the ratio of incremental power flow caused by each participant and the total power flows on a designated transmission line. To determine the individual participants impact on the transmission power flows, the line utilization factors (LUFs) of each participant are developed from a set of power flow equations. In the developed framework, one can directly evaluate the sensitivity of the flow on a line with respect to power generation at all buses. Although the developed allocation rule is very similar to the existing MW-mile method, especially to the modulus method, it does not require load flow analysis to be performed whenever each wheeling transaction is exercised. The main advantage of the developed method lies in its capability to consider multiple wheeling transactions simultaneously.

FACTS operation scheme for enhancement of power system security

This paper presents a FACTS operation scheme to enhance the power system security. Three main generic types of FACTS devices are introduced. Line overloads are solved by controlling active power of series compensators and low voltages arc solved by controlling reactive power of shunt compensators, respectively. Especially, the combined series-shunt compensators such as UPFC are applied to solve both line congestions and low voltages simultaneously. Two kinds of indices that indicate the security level related to line flow and bus voltage are utilized in this paper. They are iteratively minimized to determine operating points of the devices for security enhancement. The sensitivity vectors of the indices are derived to determine the direction of minimum. The proposed algorithm is verified on the IEEE 57-bus system with FACTS devices in a normal condition and in a line-faulted contingency.

Enhancement of power system security level through the power flow control of UPFC

This paper presents a new UPFC operation algorithm to find the operating point of UPFCs for the system security level enhancement. The proposed algorithm iteratively minimizes the security index which indicates the overload level of transmission lines. The sensitivity representing the change of the index for a given set of changes in the UPFC real power outputs is derived. In each iteration, with this sensitivity, the proposed algorithm finds a new UPFC opening point that reduces the index or increases the security margin. The algorithm is verified by the IEEE 39 bus system with multiple UPFCs. The study results show that the power flow congestion can be relieved in a normally operating system and the security margin can be guaranteed even in an over loaded or faulted condition by applying the proposed operation algorithm to UPFCs.

A decoupled unified power flow controller model for power flow considering limit resolution

A decoupled UPFC model is used for power flow. Both ends of UPFC may be assigned as PV buses or PQ buses with the desired values. Then the power flow of the power system with UPFC is performed without modifying any conventional power flow program by the model only with the addition of two buses per one UPFC. After power flow, the equations to obtain the internal UPFC states are derived. The UPFC states calculated by the power flow may not be allowed because of the UPFC limit due to the rating of inverters. In this case, the UPFC parameter values should be revised to resolve the limit. In this paper, when the series voltage magnitude and/or the shunt current magnitude are violated, the iterative methods to resolve the limits are proposed. When resolving the series voltage magnitude, three strategies are proposed according to the priority of the active power and the voltage magnitude.

An operation scheme of UPFC's considering operating objectives and states

This paper presents an operation scheme of UPFCs considering objectives and states of power system operation. Two modes of UPFC operation, an economic mode and a secure mode are proposed according to operating objectives and states. In the economic mode, both the generation cost and the active power loss have been minimized by active and reactive power control of UPFCs. In the secure mode, the security index J relating to line flows and bus voltages has been minimized by operation of UPFCs. A decoupled model has been utilized as a mathematical model to evaluate the effect of an UPFC on a system. For verification of the proposed operation scheme, numerical simulations have been performed on a 10-unit, 39-bus New England System equipped with 3 UPFCs.

Preventive and corrective operation of FACTS devices to cope with a single line-faulted contingency

This paper presents how to find proper operating points of FACTS devices to enhance the steady-state security level considering line contingency analysis. Three generic types of FACTS devices such as series controllers shunt controllers, and series-shunt controllers are introduced and applied to enhance a security margin and to minimize security indices. Quantities (MW) of security margin are depicted in a PV curve and security indices related to line flows and bus voltages are utilized and minimized iteratively in this paper. Contingency analysis is performed to detect the severest line fault in a power system. In this system condition, FACTS devices are tested to establish appropriately preventive or corrective action without generation re-dispatching or load shedding. The FACTS operation scheme is verified on the 9-bus system and the IEEE 57-bus system in a line-faulted contingency.

UPFC operation for the minimization of power production and delivery costs

This paper presents a new operation scheme of UPFCs to minimize power production and delivery costs. In the normal operation state of a power system, the production costs of active power can be minimized by economic power dispatch, and delivery costs due to transmission system loss can be also minimized by active power control of UPFC, incorporated with minimization of production cost. In order to determine amounts of active power reference of each UPFC required for the cost minimization, an iterative optimization algorithm based on the power flow calculation using the uncoupled UPFC model is proposed. For verification of the proposed method, intensive studies have been performed on a 5-bus sample system and a 10 unit 39-bus New England System equipped with UPFCs.

A refined Differential Current Protection Method in the FACTS-compensated line

This paper proposes a refined Differential Current Protection Method (DCRM) to solve problems associated with malfunction or error in relay response caused by operation of FACTS devices. The FACTS devices of interest include STATCOM, SSSC and UPFC. Analytical models and methods are presented to analyze impacts of those compensation devices on the transmission system for these devices. A variety of faults cases are studied with the proposed methods and simulation results are provided as well.

The Line Flow Control of Multiple UPFCs for Enhancing Power System Security

This article presents a method to determine operating points of Unified Power Flow Controllers (UPFC), the line flow control of which can enhance system security level. The decoupledmodel has been employed as a mathematical model of UPFC for power flow analysis so as to analyze the effect of these devices on the power system. The security index that indicates the congestion level of transmission line has been proposed and minimized by iterative method. The sensitivity of objective function for control variables of an UPFC has been derived, and it represents the change in the security index for a given set of changes in real power outputs of UPFC. The proposedalgorithmwithsensitivity analysis gives the optimalset of operatingpoints of multiple UPFCs that reduces the index or increases the security margin, and Marquart method has been adoptedas an optimization methodbecause of stable convergence. The algorithm is verified by the 10-unit, 39-bus New England system that includes multiple UPFCs. The simulation results show that the power flow congestion can be relieved in the normal state and the security margin can be guaranteed even in a fault condition by the cooperative operation of multiple UPFCs.

Derivation of Distributed Generation Impact Factor in a Networked System in Case of Simultaneous Outputs of Multiple Generation Sites

A new measure, the distributed generation impact factor (DGIF), is used for evaluating the impact of newly introduced distributed generators on a networked distribution or a transmission system. Distribution systems are normally operated in a radial structure. But the introduction of distributed generation needs load flow calculation to analyze the networked system. In the developed framework, the potential share of every generation bus in each line flow of a networked system can be directly evaluated. The developed index does not require the solution of power flow equations to evaluate the effect of the distributed generation. The main advantage of the developed method lies in its capability of considering simultaneous outputs of multiple generation sites.