Power engineers are currently facing challenges to increase the power transfer capabilities of existing transmission system. Flexible AC Transmission system (FACTS) controllers can balance the power flow and thereby use the existing power system network most efficiently. Because of their fast response, FACTS controllers can also improve the stability of an electrical power system by helping critically disturbed generators to give away the excess energy gained through the acceleration during fault. Thyristor controlled series compensator (TCSC) is an important device in FACTS family, and is widely recognized as an effective and economical means to solve the power system stability problem. TCSC is used as series compensator in transmission system. In the present work a TCSC controller is designed and tested over a single machine infinite bus (SMIB) as well as a multi-machine power system. Detailed simulation studies are carried out with MATLAB/SIMULINK environment and the effect of the TCSC parameter variations over the system stability is studied.