International Journal of Current Trends in Engineering & Technology ISSN: 2395-3152 Volume: 03, Issue: 01 (JANUARY– FEBRUARY, 2017) 16 Simulation Analysis of FACTs Devices for Transient Stability Improvement in Multi Machine System Kunal Gupta 1 , Prof. Yogesh Pahariya 2 Department of Electrical and Electronics Engineering RKDF College of Engineering Bhopal Abstract:- Transient stability control plays an important role in ensure the stable operation of power systems in the experience of large disturbances and faults, and is thus an important area of research. This paper investigates relationship of SVC, STATCOM and UPFC performance for the transient stability improvement of the power system. The enhancement of transient stability of the power system, using SVC (Static VAR Compensator), STATCOM (Static Synchronous Compensator) and UPFC (Unified Power Flow Controller) which is an effective FACTS (Flexible AC Transmission System) device able of controlling the active and reactive power flows in a transmission line by controlling appropriately parameters. Simulations are carried out in Mat lab/ Simulink environment. The presentation of SVC, STATCOM& UPFC is compared from each other. So for the improvement of transient stability STATCOM is superior to SVC. The simulation results demonstrate the value and robustness of the proposed STATCOM, UPFC& SVC on transient stability improvement of the system. Keywords: FACTS, SVC, STATCOM, UPFC, Mat lab / Simulink, Transient stability. I. INTRODUCTION Modern power system is a difficult network comprise of numerous generators, transmission lines, variety of loads and transformers. As an effect of increasing power demand, some transmission lines are more loaded than was intended when they were built. With the increased loading of long transmission lines, the difficulty of transient stability after a major fault can become a transmission limiting factor [1]. Now power engineers are much more afraid about transient stability problem due to blackout in northeast United States, Scandinavia, England and Italy. Transient stability refers to the ability of a system to maintain synchronous operation in the event of large disturbances such as multi-phase short-circuit faults or switching of lines [2]. The resulting system answer involves large excursions of generator rotor angles and is influenced by the nonlinear power angle relationship. Stability depends ahead both the initial operating conditions of the system and the severity of the disturbance. Latest development of power electronics introduces the use of flexible ac transmission system (FACTS) controllers in power systems. FACTS controllers are able of controlling the network condition in a very fast manner and this feature of FACTS can be exploited to improve the voltage stability, and steady state and transient stabilities of a difficult power system [3-4]. This allows increased utilization of existing network closer to its thermal loading capacity, and thus avoiding the require to construct new transmission lines. Static VAR Compensator (SVC) is a first generation FACTS device that can control voltage at the required bus thereby improving the voltage profile of the system. The main task of an SVC is to maintain the voltage at a particular bus by means of reactive power compensation (obtained by varying the firing angle of the thyristors) [5]. SVCs have been use for high performance steady state and transient voltage control compared with standard shunt compensation. SVCs are also used to dampen power swings, improve transient stability, and decrease system losses by optimized reactive power control [6-7].STATCOM, a shunt compensation device, from the family of flexible alternating current transmission systems (FACTS). The STATCOM is a solid-state voltage source converter which is tied to a transmission line. A STATCOM injects an almost sinusoidal current, of changeable magnitude, at the point of connection. This injected current is approximately in quadrature with the line voltage, thereby emulating an inductive or a capacitive reactance at the point of connection with the transmission line. The profit of utilizing FACTS devices in electrical transmission systems can be summarize as follows: 1. Better utilization of presented transmission system assets 2. improved transmission system reliability and availability 3. Increased dynamic and transient grid stability and decrease of loop flows 4. Better quality of supply for sensitive industries Environmental profit. 2. STATIC VAR COMPENSATOR (SVC) Static VAR systems are applied by utilities in transmission applications for several purposes. The primary purpose is usually for rapid control of voltage at weak points in a network. Installations may be at the midpoint of transmission interconnections or at the line ends. Static VAR Compensators are shunting connected static generators / absorbers whose outputs are different so as to control voltage of the electric power systems. In its easy form, SVC is connected as Fixed Capacitor Thyristor Licensed Under Creative Commons Attribution CC BY Controlled Reactor (FC-TCR) configuration as shown in Figure 1. The SVC is connected to a coupling transformer that is linked directly to the ac bus whose voltage is to be regulated. The efficient reactance of the FC-TCR is varied by firing angle control of the anti-parallel thyristors. The firing angle can be controlled during a PI (Proportional + Integral) controller in such a way that the voltage of the