[Yadav, 3(9): September, 2014] ISSN: 2277-9655 Scientific Journal Impact Factor: 3.449 (ISRA), Impact Factor: 2.114 http: // www.ijesrt.com (C)International Journal of Engineering Sciences & Research Technology [27] IJESRT INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY Improvement of Transient Stability with SSSC Controller in a Three-Machine Power System for Asymmetrical Faults Ravi Kant Yadav*, V. K. Giri * Dept. of Electrical Engineering, MMMUT, Gorakhpur, India Professor and Head, Dept. of Electrical Engineering, MMMUT, Gorakhpur, India ravikant920110@gmail.com Abstracts An Improvement of transient stability performance with the help of Static Synchronous Series Compensator (SSSC) controller has been presented in this paper. The SSSC is used to control active and reactive powers as well as damping power system oscillations in transient mode. The results obtained from simulations validate the effectiveness of proposed modeling and tuning approach for power system stability improvement. The simulation results also show that the proposed SSSC controller is effective in the asymmetrical disturbance conditions in the power system. The obtained results justify that the proposed SSSC controller is found to be robust for fault location and change in operating conditions. For the simulation purpose, the model of three-machine power system with SSSC controller has been developed in MATLAB/SIMULINK using Sim Power System (SPS) block set. Keywords: Three-machine power system; static synchronous series compensator (SSSC); transient stability. Introduction Series capacitive compensation was introduced decades ago to cancel a portion of the reactive line impedance and there-by increase the transmittable power [1]. The recent development of power electronics introduces the use of Flexible AC Transmission System (FACTS) controllers in power systems [2]. Subsequently, within the FACTS initiative, it has been demonstrated that variable series compensation is highly effective in both controlling power flow in the lines and in improving stability [3, 4]. The voltage source converter based series compensator, called static synchronous series compensator (SSSC) provides the virtual compensation of transmission line impedance by injecting the controllable voltage in series with the transmission line[5, 6]. Static Synchronous Series Compensator (SSSC) has been one of the important members of FACTS family which may be installed in series in the transmission lines. The ability of SSSC to operate in capacitive as well as inductive mode makes it very effective in controlling the power flow of the system [7, 8]. With the capability to change its reactance characteristic from capacitive to inductive, the SSSC is very effective in controlling power flow in power systems [9, 10]. An auxiliary stabilizing signal can also be superimposed on the power flow control function of the SSSC so as to improve power system oscillation stability [11, 12]. The applications of SSSC for power oscillation damping, stability enhancement and frequency stabilization can be found in several references [13-19]. Power system model The three-machine power system with SSSC has been shown in Fig. 1 is consider in this paper. The system consists of three generators divided into two subsystems and are connected through an inter-tie line. The generators are equipped with hydraulic turbine and governor (HTG) and excitation system. The HTG represents a nonlinear hydraulic turbine model, a PID governor system, and a servomotor. The excitation system consists of a voltage regulator and DC exciter, without the exciter’s saturation function. In this system asymmetrical fault disturbance, the two subsystems swing against each other resulting as instability. To improve the stability the line is sectionalized and a SSSC is assumed on the mid-point of the tie-line. In Fig. 1, 1 G , 2 G and 3 G represent the generators; 1 / , T F 2 / T F and 3 / T F represent the transformers and 1 L , 2 L and 3 L represent the line sections respectively. Bus 1 are connected to inductive load and bus 2, bus 3, bus 4 are connected with resistive load.