AbstractThis paper proposes the coo

Abstract
This paper proposes the coordinated operation of optimal reclosing of circuit breakers and Static Var Compensator (SVC) for enhancing the transient stability of a multi-machine power system. The transient stability performance of the combined operation of optimal reclosing of circuit breakers and SVC is compared with that of the combined operation of conventional reclosing of circuit breakers and SVC. The total kinetic energy (TKE) of the generators in the system is used to determine the transient stability enhancement index. Simulations are performed through Matlab/Simulink software. Simulation results for both the three-line-to-ground (3LG) and single-line-to-ground (1LG) permanent faults at different points of the power system indicate that the proposed combination of optimal reclosing of circuit breakers and SVC can enhance the transient stability of the system well. Also, the performance of the proposed method is better than that of the combined operation of conventional reclosing of circuit breakers and SVC.
Keywords
• Optimal reclosing of circuit breakers (ORCT);
• Permanent fault;
• Static Var Compensator (SVC);
• Total kinetic energy (TKE);
• Transient stability
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1. Introduction
Transient stability refers to the ability of a power system to maintain synchronism following major disturbances. In case of faults on the transmission line, the circuit breakers act to protect the healthy section by opening, and maintain continuity of power by reclosing after the fault arc de-ionization . In most of the cases, the circuit breakers are reclosed at high speed after a fixed time interval.
A conventional reclosing technique depicts the reclosing of circuit breakers after a prescribed time period, when the arc between the fixed contact and moving contact might or might not persist. However, if the arc persists, especially in case of a permanent fault, then the circuit breaker would not be able to reclose successfully and will sectionalize the system, which is an indication of the unstable state of the system. Since transient stability is also dependent on the generator state of reclosing, to maintain the synchronism and enhance the transient stability we have to find out an optimal reclosing time when reclosing of the circuit breakers will enhance the transient stability of the system effectively and
Static Var Compensator (SVC) is a Flexible AC Transmission System (FACTS) device which is connected in shunt with the power system. Although SVC is primarily used for compensating the bus voltage by injecting or absorbing the reactive power, but it also has the capability of improving the transient stability of the power system. SVC can limit the damping of power system by utilizing the first swing accelerating and decelerating area of the generators load angle and SVC with the presence of the power electronic devices can control the unbalanced loads more effectively and can enhance the transient stability of the system by inserting or absorbing instantaneous currents to or from the system.
Both the optimal reclosing of circuit breakers and SVC independently are proven methods [7], [8], [10] and [11] for improving the transient stability of power system, but there is no work concentrating on their combined effect on the transient stability of multi-machine power system. This work proposes the combined operation of SVC and optimal reclosing of circuit breakers to enhance the transient stability of the power network, and this is the original contribution of this work. In order to evaluate the effectiveness of the proposed methodology in more detail, its performance is compared to the performance of the combined operation of SVC and conventional reclosing of circuit breakers.
In our previous work [12], we considered the total kinetic energy based optimal reclosing of circuit breakers for power system transient stability improvement. In this research, we also considered the same optimal reclosing technique. The method has an advantage that it uses the kinetic energy of the generators which can be easily obtained in real time. Moreover, for multi-machine power system, different generators have different speed characteristics. So, the total kinetic energy technique utilizes the summation of the kinetic energy of every generator in the system. In this method, the time when the total kinetic energy oscillation of the generators without reclosing operation becomes the minimum is determined as optimal reclosing time (ORCT).
The effectiveness of the proposed methodology is tested considering permanent balanced and unbalanced faults at different locations of the IEEE nine bus power system model [11], [12], [13] and [14]. The total kinetic energy (TKE) of the generators in the system is used to determine the transient stability enhancement index. In this work, simulations are performed through Matlab/Simulink software.
The organization of this paper is as follows: Section