Damping Subsynchronous Resonance Using a Static Synchronous Series Compensator Based Supplementary Damping Controller

This paper investigates the effectiveness of a supplementary damping controller around a Static Synchronous Series Compensator (SSSC) in mitigating the torsional oscillations due to interaction of series compensated transmission line with the nearby turbine-generator shafts. The main objective of the controller is to suppress the unstable torsional oscillations with frequencies coinciding with the turbine-generator shaft torsional modes, through modulation of the reactance provided by the SSSC. Detailed simulation studies are done in Power System Computer Aided Design (PSCAD) using a single machine infinite bus (SMIB) power system adopted from the IEEE first benchmark model (FBM) for subsynchronous resonance analysis. The results show that this supplementary damping controller can provide positive damping to the unstable torsional oscillations due to presence of conventional series capacitors in the line or an SSSC or a combination of both the SSSC and conventional series capacitor banks.