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In an AC transmission system power flow can be controlled by injecting a compensating voltage in series with the line. Thyristor controlled series compensator (TCSC) are utilized as a conventional means for the purpose while unified power flow controller (UPFC) is the latest converter based devices employing fast power electronic equipments. This paper utilizes the steady state model of thyristor controlled series capacitor and a unified power flow controller for series voltage compensation, and evaluating their range of power flow control for simple network. The models are incorporated into the existing Newton Raphson load flow algorithm. The iterative equations of the Newton Raphson load flow algorithm are modified by the device parameters and the combined set of power flow equations and UPFC or the TCSC control equations are solved for convergence of the formula. Matlab codes are utilized for the implementation of the two devices in the Newton-Raphson algorithm. Power flow control ranges are evaluated for few IEEE bus systems and standard 5 bus system. Results are reported and studies are presented to illustrate and compare the effectiveness of the UPFC and TCSC.