The transmission system is responsible for transporting the electric power generated at therngeneration station to the distribution system. When a power transmission system works withrnseverely loaded lines, it suffers from power losses and larger voltage deviations, which can causernthe system to malfunction and eventually collapse. Capacitor banks and STATCOM are used inrnthis thesis in order to reduce line loss and enhance the voltage of the considered system. Thernpower flow analysis using the Newton-Raphson algorithm in MATLAB software and particlernswarm optimization techniques are utilized to determine the optimal devices sizing and position.rn The result shows that, with proper placement of the Capacitor banks and STATCOM on thernidentified candidate buses (68, 65, 27, 20) with their optimal sizes, the active power losses of thernsystem gets improved by 10.78%, 20.57%, 35.84%, 6.602% and 10.76%, 22.29%, 37.79% ,rn7.76% in the scenarios of base load, 25% overload, 50% overload and 75% underloadrnrespectively. In scenarios of base load, 25% overload, 50% overload and 75% underload thernvoltage magnitudes of weak buses are also improved by 12.5%, 19.41%, 31.15%, 3.23% andrn17.5%, 22.8%, 31.4%, 9.84% after the incorporation of Capacitor banks and STATCOMrnrespectively. The improvements made by the placements of Capacitor banks and STATCOM inrnthe 75% underload case are not so much significant as the network is almost in a desirablernoperating condition under this scenario. Thus, the placement of those FACTS devices forrnunderload (75% of base load) is not recommended.rn The amount of energy cost saved after installing Capacitor bank is 1,825,856.88726 USD,rn2,282,320.79712 USD, 2,518,262.57088 USD with Payback periods of 0.516 years, 0.186 yearsrnand 0.0579 years in the scenarios of base load, 25% overload and 50% overload respectively.rnAnd after installing STATCOM, the amount of energy cost saved is 15,339,987.264 USD,rn31,399,157.216 USD, 33,744,416.832 USD with Payback periods of 4.344 years, 2.369 yearsrnand 0.485 years in the scenarios of base load, 25% overload and 50% overload respectively. rn In general, for power loss minimization and voltage profile enhancements, STATCOM isrnproposed for the system due to its better performance during overload as observed from thernsimulation results, manages over voltage at under load case and its dynamic capability to injectrnreactive power based on the required reactive load.