Obtaining optimal power flow has been a challenge over the years for power system engineers. Several ways and technologies ranging from conventional to the use of modern Flexible Alternating Current Transmission Systems (FACTS) devices have been incorporated into the power system to ensure optimal flow of power. FACTS devices used are capable of mitigating several power system problems ranging from line overloading, voltage instability, transient instability, and Power system congestion and so

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... n. Phase shifting transformer (PST) is a FACTS device that is capable of controlling power flow problems in a network by varying its phase angle. PST, when installed at appropriate locations on the power system is capable of redirecting and redistributing power flow from overloaded lines to the less loaded ones, hence ensuring an optimal performance and improved performance of the power system.This paper evaluates the effect of incorporating the PST on the IEEE 5 bus system. Newton-Raphson load flow technique is employed in modeling the IEEE 5 bus system and the PST. Simulation was carried out using MATLAB software package for both the steady state condition and with the incorporation of PST. Results showed that overloading on some transmission lines was checked and mitigated by redistribution of active power across the system. There was also reduction of losses on the lines. INTRODUCTION Over the years, power system security has been constantly threatened as a result of an ever increasing load being added to the system, failure of one or more system components, transients. Increased power demand poses serious challenge to the load handling capability of the power system as an outage of transmission line failure may result in overload on other lines [16] . Consequently, this may have a cascaded failure of the transmission lines, hence, resulting in partial or total system collapse. Overloading on of transmission lines in the power system can be mitigated by appropriate redistribution of power flow from the overloaded lines to the less loaded lines. One of the effective techniques used to control power flow in a system is the installation of phase shifting transformers (PST) on appropriate lines. PST is FACTS device controls the active power flow by means of varying its phase angle between the primary side voltage and the secondary side voltage. This helps to regulate the flow of power on the lines and between the buses in the power system [14] . This phase shift of the PST controls the active power flow, both in magnitude and direction [1] . Power flow analysis is mostly important for system planning and operation in order to improve power quality. They notify and detect components that are over-loaded in the voltage profiles. Also, power flow system can be applied to analysis reliability index and forecast the future load demand in the system. [6, 13] . The highly common methods of power flow are Gauss-Seidel and Newton-Raphson which are widely used in transmission systems but produce worse robustness and performance when applied to distribution system [5] . This occurs due to distribution nature of the network which is design through feebly meshed topology or a dial and very high R/X ratio. There are many proposed methods to minimized these problems, such as backward-forward sweep and Zbus Gauss techniques [12, 19] . Moreover the direct approach (DA) also proposed which is the very efficient and unique [20] . The direct approach (DA) technique save time for performing LU factorization which involves backward and forward substitution of the admittance matrices or jacobian, which are commonly manual formulations. Thus, the design of direct approach (DA) allows the application of real-time in the smart grid. Therefore, reference [4] used DA methods to analyze optimal power flow (OPF) in FACTS distribution network for industrial grid. In reference [3] the three-phase method applied perform sequentially the mutual couplings and selfimpedances for the operation but shunt admittances are nullified. The lines system design is always short-length and non-tapped transformers even when the power flow analysis run at minimum voltage levels of the distribution network when shunt admittances limits the operations of high voltage levels. The application of power analysis in a network grid is to post-process phase voltage angles through transformer phase shifting. Hence, the technique cannot be applied if the meshed grid network is weak. Therefore the transformer phase shifting model is now applied to control the operation of active power flow through power transformer in the loop. The phase shifting