International Journal of Electrical Electronics & Computer Science Engineering Volume 4, Issue 6 (December, 2017) | E-ISSN : 2348-2273 | P-ISSN : 2454-1222 Available Online at www.ijeecse.com 68 Review of Transient Stability Enhancement in Multi-Machine Power System by using Various Types of PSS & FACT’s Devices G. B. Jadhav 1 , Dr. C. B. Bangal 2 , Dr. Sanjeet Kanungo 3 1 Ph.D. Scholar, Dr.Babasaheb Ambedkar Marathwada University, Aurangabad, Maharashtra 2 Professor & Principal, RMD, Shinhgad School of Engineering, Pune, Maharashtra 3 Professor & Program Chair Marine Engineering, Tolani Maritme Institute, Pune, Maharashtra gyandevj@tmi.tolani.edu, charudatta_bangal@yahoo.com, sanjeetk@tmi.tolani.edu Abstract: This paper presents review of various techniques used for enhancement of power system stability. Various combinations of PSS’s and FACT’s devices such as the SVC- based PID damping controller and PSS, STATCOM controller, the SVC and the generic/multiband PSS, MultiBand PSS, Dual input PSS, PSS and TCSC controllers, FLPSS, UPFC and PSS and the MB-PSS which are used for enhancing transient stability in power system are reviewed in this paper. The information collected in this paper is sufficient for finding out relevant references in the field of power system stability. Keywords: Transient Stability, FACTS controller, PSS. I. INTRODUCTION The power system is a highly nonlinear system that operates in a constantly changing environment; loads, generator outputs and key operating parameters change continually. When subjected to a disturbance, the stability of the system depends on the initial operating condition as well as the nature of the disturbance. Increasingly complex modern power systems require stability, especially for transient and small disturbances. Transient stability plays a major role in stability during fault and large disturbance.[26] The change in electromagnetic torque of a synchronous machine following a perturbation can be resolved into two components: Synchronizing torque component, in phase with rotor angle deviation. Damping torque component, in phase with the speed deviation. System stability depends on the existence of both components of torque for each of the synchronous machines. Lack of sufficient synchronizing torque results in aperiodic or nonoscillatory instability, whereas lack of damping torque results in oscillatory instability. For convenience in analysis and for gaining useful insight into the nature of stability problems, it is useful to characterize rotor angle stability in terms of the following two subcategories: Small-disturbance (or small-signal) rotor angle stability is concerned with the ability of the power system to maintain synchronism under small disturbances. In today’s power systems, small-disturbance rotor angle stability problem is usually associated with insufficient damping of oscillations. The aperiodic instability problem has been largely eliminated by use of continuously acting generator voltage regulators; however, this problem can still occur when generators operate with constant excitation when subjected to the actions of excitation limiters (field current limiters). Small-disturbance rotor angle stability problems may be either local or global in nature. The time frame of interest in small-disturbance stability studies is on the order of 10 to 20 seconds following a disturbance. Large-disturbance rotor angle stability or transient stability, as it is commonly referred to, is concerned with the ability of the power system to maintain synchronism when subjected to a severe disturbance, such as a short circuit on a transmission line. The resulting system response involves large excursions of generator rotor angles and is influenced by the nonlinear power-angle relationship. Transient stability depends on both the initial operating state of the system and the severity of the disturbance. Instability is usually in the form of aperiodic angular separation due to insufficient synchronizing torque, manifesting as first swing instability. However, in large power systems, transient instability may not always occur as first swing instability associated with a single mode; it could be a result of superposition of a slow interarea swing mode and a local-plant swing mode causing a large excursion of rotor angle beyond the first swing .It could also be a result of nonlinear effects affecting a single mode causing instability beyond the first swing. - The time frame of interest in transient stability studies is usually 3 to 5 seconds following the disturbance. It may extend to 10–20 seconds for very large systems with dominant inter-area swings.[1]-[2]-[3] Mitigation of Transient Stability Problem: The control actions at generator end to enhance the system stability are either in terms of excitation system or power system stabilizers or at mechanical end of power plants. Fig.1 show the general structure of primary control system to enhanced transient stability at generator end side in the system [19].