Damping improvement by FACTS devices: A comparison between STATCOM and SSSC

Following a disturbance, the machines in a stable power system initially oscillate, and then settle at the stable equilibrium point where the transient energy is zero. This paper uses the rate of dissipation of transient energy as a measure of system damping. The above concept is then applied to determine the additional damping provided by a static synchronous compensator (STATCOM) and a static synchronous series compensator (SSSC). Analytical expressions for additional damping provided by these devices are carefully derived and compared for classical model of a simple power system. The proposed technique of evaluating system damping is then tested on a single-machine system and for some special faults in the 10-machine New England system. The results obtained in both the systems are then systematically described.