This paper concentrates on controlling of power flow in power lines with the help of series Flexible Alternating Current Transmission Systems (FACTS) device. The power flow control deals with the task of taking remedial measures against overloads and nonlinear loads in the system due to the occurrence of contingencies. The series FACTS devices considered in this paper are Thyristor Controlled Series Capacitor (TCSC), Thyristor Controlled Phase Shifter (TCPS) and Static Synchronous Series Compensator (SSSC). This paper presents the modelling of these series FACTS devices suitable for incorporation in load flow program for the study of steady state operation of power system. A systematic foundation on the theory and practice of positive sequence power flow is presented here. An efficient Newton-Rapshon (NR) method is used for solving the nonlinear algebraic load flow equations in the load flow problem. A step by step procedure for incorporation of series FACTS devices within the NR load flow algorithm is described. The effectiveness of the proposed models and convergence of the proposed load flow algorithm is tested on standard IEEE 30 bus test network without and with these series FACTS devices. Programming for the solution of series controllable branches with these proposed models is done by using MATLAB software. Results are reported and studies are presented to demonstrate and compare the efficiency of TCPS, TCSC and SSSC.