This paper deal an AC Transmission system power flow controlled by injecting a compensating voltage in series with the line and injecting reactive power in shunt with the bus. Static Synchronous Series Compensator (SSSC) is considered as a series compensator and Static Synchronous Compensator (STATCOM) is considered as a shunt compensator, while Unified Power Flow Controller (UPFC) is considered as a series-shunt compensator. This paper covers, in depth, the simulation and modeling methods required for study of the steady-state operation of electrical power systems with these flexible AC Transmission Systems (FACTS) controllers. MATLAB® codes are used for the implementation of the three devices in the Newton-Raphson algorithm. Power flow control ranges are evaluated for IRAQI (400kV) National Super Grid System (INSGS). Results are studies and reported are presented to compare the effectiveness of the STATCOM, SSSC and UPFC.