The Available Transfer Capability (ATC) of a transmission system is a measure of unutilized capability of the system at a given time. The computation of ATC is very important to the transmission system security and market forecasting. While the power marketers are focusing on fully utilizing the transmission system, engineers are concern with the transmission system security as any power transfers over the limit might result in system instability. One of the most critical issues that any engineers would like to keep an eye on is the voltage collapse. Recent blackouts in major cities throughout the world have raised concerns about the voltage collapse phenomenon. FACTS devices such as thyristor controlled series compensators and thyristor controlled phase angle regulators, by controlling the power flows in the network, can help to reduce the flows in heavily loaded lines resulting in an increased loadability of the network and improves the voltage stability. In this paper (128 bus system of Andhra Pradesh state power grid) a real time system is tested for calculating transfer capability by using various FACTS devices like TCSC and TCPAR. The results have been presented and analyzed.