The unified power flow controller (UPFC) is the most versatile and advanced member of flexible ac transmission systems (FACTS) devices capable of controlling active-reactive power flows, as well as providing voltage magnitude control in power networks. This paper presents a study on investigating steady-state analysis of UPFC and its performance on power systems. Firstly, a mathematical model of UPFC suitable for power flow studies are derived in the form of injected powers called "modified power injection model", the model is then adopted into a power flow software called power system analysis software package (PSASP)". Computer simulations based on the IEEE 30-bus test system are proposed and results show that a UPFC embedded into a power system can handle control of the power flow problem efficiently. Finally the effects of the UPFC location on power system operations are investigated. Relevant results are presented and discussed in full.