This paper represents a method for providing series compensation to lower the inductive reactance which in turn increases the transmission line power transfer capability. Advantages of a TCSC over other series compensation devices is that the TCSC's reactance is instantaneously and continuously variable. This means that the TCSC can be used not only to provide series compensation but can also be used to enhance the stability of the power system. The TCSC consists of back to back thyristors that control the reactance of the TCSC.By changing the trigger angle of these back to back thyristors it is possible to vary the reactance of the TCSC. This book analyzes the impedance characteristics and associated single & multi resonance conditions.The capacitor voltage, line current, thyristor current and capacitor current waveforms are discussed briefly as simulation Results. Test model of TCSC device is developed and simulated for different test system data and corresponding waveforms are analyzed. The subsidiary topics e.g. power oscillation damping, SSR mitigation and transient stability is also brought out.