د.خيرية سالم بلغيث2026-06-102026-06-10https://dspace.academy.edu.ly/handle/123456789/2258The continuing rapid development of high-power semiconductor technology now makes it possible to control electrical power systems by means of power electronic devices.[2] these devices constitute an emerging technology called FACTS (flexible alternating current transmission systems), FACTS technology has a number of benefits, such as greater power flow control, increased secure loading of existing transmission circuits, damping of power system oscillations, less environmental impact and, potentially, less cost than most alternative techniques of transmission system reinforcementThe use of transmission lines for AC power is often subjected to stability problems , Transient stability control plays a significant role in ensuring the stable operation of power systems in the event of different disturbances and faults, So the enhancement of transient stability is essential for a secure power system. Transient stability of the system can be improved by placement one of the FACTS devices , such as the Unified Power Flow Controller ( UPFC ) , which have a unique capability to control simultaneously real and reactive power flows on a transmission line , and creates a tremendous quality impact on power system stability .Unified Power Flow Controller