2022 1 Enhancements of Transient stability for Synchronous Generator using Fuzzy Logic Controlled power system stabilizer [Case Study in Tana Beles Hydropower Plant] Gedef Yirgalem Sharie School of Electrical and Computer Engineering, Woldia Institute of Technology,Woldia University, Woldia, Ethiopia ABSTRACT The power system is constantly subjected to numerous forms of disruptions, resulting in a loss of stability. The cause of instability is a large disturbance. The "large disturbance" leads to electromechanical oscillations in a synchronous generator. For this problem, the Tana Beles hydropower plant uses AVR to enhance transient stability of synchronous generators under faulty conditions. However, with the creation of large disturbances, this regulator gives poor performance due to long settling time and maximum overshoots. In this paper, power system transient instability of synchronous generators found in the Tana Beles Hydropower plant was introduced in faulty conditions. Which were damped out quickly by using a fuzzy logic-controlled power system stabilizer (FLPSS). FLPSS is implemented in the excitation systems of synchronous generators to damp electromechanical oscillations of the study under wide operating conditions. FLPSS reduces settling time and greatly damps electromechanical oscillations of rotor speed, load angle, electrical torque, and active power of synchronous generators. The paper deals with the design procedure for a fuzzy logic-controlled power system stabilizer (FLPSS) which improves the transient stability of synchronous generators. The speed deviation of a synchronous machine and acceleration are chosen as the input signals to the fuzzy logic controller. During a fault condition, FLPSS enhances the settling time of rotor speed, load angle, active power, and electrical torque by 77.7%, 50%, 88%, and 76.5% respectively. Similarly, FLPSS reduces the overshoots of generator parameters of rotor speed, load angle, and terminal voltage by 7.7%, 3.1%, and 14.26% respectively. The comparison was done between the excitation systems with AVR and FLPSS using MATLAB/Simulink software. Keywords: AVR, FLPSS, MATLAB /Simulink and Transient Stability 1. Introduction Power systems are the largest and most complicated dynamic systems, and they are continuously subjected to disturbances and experience transitions from one operating point to another in the form of oscillations. The oscillations must be damped as a basic condition for the power system to retain stability. The power system stability has been an important preoccupation for engineers since the 1920s. Despite significant advancements in management and protection technology, power system blackouts continue to occur because of instability. Power system stability refers to an electric power system's capacity to return to a state of operating equilibrium following a physical disturbance, with most system variables limited so that practically the entire system remains unaffected [1]. Based on the magnitude of the disturbance, three types of power system stability can be distinguished: steady state stability, dynamic stability, and transient stability. This study, however, focuses on "transient" stability, which is concerned with the power system's capacity to sustain synchronism in the presence of numerous transient disturbances. Such kinds of disturbances are mainly caused for electromechanical oscillations. For instance, at Tana Beles hydropower plant, total system blackouts were registered on October 14, 2022; from 10:30 a.m. to 3:00 p.m. due to an earth fault on the Beles to Bahir Dar transmission line one. At this time, a 400 kV line one circuit breaker opened, and the generators were subjected to electromechanical oscillations. Generator failures, outages, power interruptions, and total system blackouts are all caused by electromechanical oscillations. This results in a reduction in system component lifetime, a loss of synchronism, and, in the worst-case scenario, the risk of partial system collapse. AVR is used by the Tana Beles hydroelectric project to maintain the output terminal voltage of the generators, but it only works to a certain extent. As a result, such a stabilizer has the drawback of being unable to function under various disturbances. Fuzzy logic is an effective technology used today for maintaining stability of electrical systems. Primarily, it depends on the degree of truth. Truth sets enable objects to receive membership grades ranging from 0 to 1 (true or false). These sets are primarily expressed in terms of the linguistic variables that are typically employed to represent a particular fuzzy set in a stability problem. A fuzzy logic controller has seen widespread use in the power sector recently. There have been numerous reports about the fuzzy control theory-based PSS design. Due to its effectiveness and simplicity, a fuzzy logic-based PSS is preferred for improving transient stability. Therefore, this paper uses a fuzzy logic based power system stabilizer which is superior to the other power system