• Journal of Electrical Engineering and Technology
• /
• v.10 no.3
• /
• pp.877-887
• /
• 2015

Rapid development of cities with constant increasing load and deregulation in electricity market had forced the transmission lines to operate near their threshold capacity and can easily lead to voltage instability and caused system breakdown. To prevent such catastrophe from happening, accurate readings of voltage stability condition is required so that preventive equipment and operators can execute security procedures to restore system condition to normal. This paper introduced Enhanced Hybrid Particle Swarm Optimization algorithm to estimate the voltage stability condition which utilized Fast Voltage Stability Index (FVSI) to indicate how far or close is the power system network to the collapse point when the reactive load in the system increases because reactive load gives the highest impact to the stability of the system as it varies. Particle Swarm Optimization (PSO) had been combined with the ANN to form the Enhanced Hybrid PSO-ANN (EHPSO-ANN) algorithm that worked accurately as a prediction algorithm. The proposed algorithm reduced serious local minima convergence of ANN but also maintaining the fast convergence speed of PSO. The results show that the hybrid algorithm has greater prediction accuracy than those comparing algorithms. High generalization ability was found in the proposed algorithm.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.51 no.11
• /
• pp.568-576
• /
• 2002

This paper presents a new algorithm for the enhancement of voltage stability by optimal routing (OR) technique. A new voltage stability index (VSI) for optimal routing is also proposed by using theories of critical transmission path based on voltage phasor approach and equivalent impedance method. Furthermore, the proposed algorithm automatically detect the critical transmission path to critical transmission path to critical load which are faced to voltage collapse due to additional real or reactive loading. We also adopt a improved branch exchange (IBE) algorithm based on a tie branch power (TBP) flow equation to apply the OR technique. The proposed IBE algorithm for the VSI maximizing can effectively search the optimal topological structures of distribution feeders by changing the open/closed states of the sectionalizing and tie switches. The proposed algorithm has been evaluated with the practical IEEE 32, 69 bus test systems and KEPCO 148 bus test system to show favorable performance.

• Proceedings of the KIEE Conference
• /
• 2005.07a
• /
• pp.359-361
• /
• 2005

This paper presents the method of countermeasures before voltage collapse by load encroachment(impedance of load ability on R-X locus decrease toward zero point) and describes a study of impedance relay(zone-3) operation and voltage instability caused by over load of neighborhood line at contingency of heavy load line.

• Proceedings of the KIEE Conference
• /
• 2002.07a
• /
• pp.44-46
• /
• 2002

Service restoration following a complete or partial collapse starts with reenergize a transmission line from black-start generators. Voltage problems can arise by Ferranti effect as unloaded transmission line is reenergized. This paper presents analytical results on the primary restorative transmission system focused on the voltage problem during the early restoration process. Methodologies to handle load pick-up compensating Ferranti effect. and terminal voltage and reactive capability limitation of black-start generators about self-excitation are presented. An algorithm for static analysis about these methodologies is developed, and EMTDC simulation for verifying the efficiency of the algorithm is performed.

• Proceedings of the KIEE Conference
• /
• 1992.07a
• /
• pp.145-148
• /
• 1992

The best index should show the margins to the operating limit at the present operating point without much efforts. Such voltage collapse proximity index has been proposed in this study. Differently from the normal procedure in which every bus load is increased at the same propotion, bus load increase toward the direction of T/L loss increase has been applied in this study. Sample studies show the usefulness and the practical applicability in voltage stability analysis.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.35D no.3
• /
• pp.1-10
• /
• 1998

A new oscillator configuration is presented and tested for Josephson voltage standard operated at the cryogenic(4.2K) temperature. Features of active devices are investigated in aspects of 1/f noise, output power, and current collapse at low temperature. The output power of oscillator is optimized by a nonlinear design approach called Harmonic Two Signal Method(HTSM). The embedding newworks of the generalized six oscillators with tow loads are derived. A HEMT oscilliator is designed in X-Band for the Josephson voltage standard and tested at room and cryogenic(4.2K) temperatures. Oscillation frequency, output power, C/N ratio, and fequency stability are compared at room and low temperatures.

• Proceedings of the KIEE Conference
• /
• 1996.11a
• /
• pp.77-79
• /
• 1996

This paper presents an integrated stability analysis by the direct energy function method based on Equivalent Mechanical Model(EMM) which reflects the system behavior related to both angle and voltage stabilities. Actually, angle and voltage stability are intimately related in power system, so complete decoupling of these stability analysis is not possible in general, particularly in stressed power systems. In this paper, it is shown that a identical energy function can be used for angle and voltage stability analysis. The proposed energy function reflects the line resistances and reactive powers under the constraints of the same R/X ratio. The energy margin between UEP and SEP presents a good collapse proximity index in both types of stability analysis.

• Proceedings of the KIEE Conference
• /
• 1996.11a
• /
• pp.80-83
• /
• 1996

This paper develops a method for reliably estimating an UEP(Unstable Equilibrium Point) which is located in the direction of SEP(Stable Equilibrium Point)'s moving as system load is getting heavy. As power systems are getting loaded heavily, the SEP which is an operable solution, and the UEP which is occurring voltage collapse, are moving toward each other linearly. The estimated UEP is used as a good initial guess for the real UEP. The proposed method is tested by 3 bus system and Stagg 5 bus system. It is demonstrated that the proposed method is very useful for assessing system voltage stability in the case of heavy loaded power system. The result solutions are often used in conjunction with energy methods and the stability margin.

• Journal of Electrical Engineering and Technology
• /
• v.12 no.5
• /
• pp.1689-1696
• /
• 2017

In recent academic and industrial circles of the Republic of Korea, the securement of available reactive power reserve against the line faults is at issue. Thus, simulations have been performed for the securing of effective reactive power reserve (effective Q) to prepare for the line faults and improve reactive power monitoring and control methods. That is, a research has been conducted for the fast-decoupled Newton-Raphson method. In this study, a method that distinguishes source and sink regions to carry out faster provision of information in the event of line fault has been proposed. This method can perform quantification with the formula that calculates voltage variations in the line flow. The line flow and voltage changes can be easily induced by the power flow calculation performed every second in the operation system. It is expected that the proposed method will be able to contribute to securement of power system stability by securing efficient reactive power. Also, the proposed method will be able to contribute to prepare against contingencies effectively. It is not easy to prepare quickly for the situation where voltage drops rapidly due to the exhaustion of reactive power source by observing voltage information only. This paper's simulation was performed on the large scale Korean power system in steady state.

• Proceedings of the KIEE Conference
• /
• 2002.07a
• /
• pp.87-89
• /
• 2002

This paper presents a new approach using an Improved branch exchange (IBE) technique to maximize the voltage stability as well as loss minimization in radial power systems. A suitable voltage stability index (VSI) for optimal routing algorithm is developed using novel methods both a critical transmission path based on a voltage phasor approach and an equivalent impedance method. Furthermore, the proposed algorithm can automatically detect the critical transmission path to be reached to a critical load faced with voltage collapse due to additional real or reactive leading. To develop an effective optimization technique, we also have applied a branch exchange algorithm based on a newly derived index of loss change. The proposed IBE algorithm for VSI maximization can effectively search the optimal topological structures of distribution feeders by changing the open/closed states of the sectionalizing and tie switches. The proposed algorithm has been tested with the various radial power systems to show its favorable performance.