eries capacitors belong to the conventional series compensators in power systems. They are used for compensation of the inductive reactance of the transmission lines. Series capacitors improve the system stability margin; moreover, they control active power flow among parallel transmission lines. Series capacitors, however, may increase the risk of an adverse phenomenon called Sub-Synchronous Resonance (SSR). SSR is an electric power system circumstance in which the electric network exchanges energy with the generator. The frequency of this exchange is below the synchronous frequency. in this situation, the turbine-generator oscillates at a frequency corresponding to the torsional mode frequency. Sub-Synchronous Resonance (SSR) in a long transmission line leads to the failure of the turbine shaft if not damped properly. STATic COMpensator (STATCOM) is a multifunctional FACTS device which has different applications in power system. The main purpose of this thesis is to design a sub-synchronous resonance damping controller with local signal for a STATCOM in a different place of the transmission line. For a STATCOM in a transformer bus and near the generator, the controller is designed based on generator speed deviation damping signal and the performance of this controller is studied in different operation conditions. But in a situation that STATCOM is located far from the generator, it can’t use speed deviation damping signal for the controller .Therefore, another damping signal must be used for damping sub-synchronous resonance. In this thesis, it is demonstrated that reactive current signal of the transmission line has a good performance for damping sub-synchronous resonance and for the first time this signal is applied in damping sub-synchronous resonance. In this thesis, IEEE First Benchmark system is considered. Also for analysis of sub-synchronous resonance and for performance investigation of the proposed controllers, some modified IEEE First Benchmark systems with several parallel turbine-generators and also with several series compensated transmission line have been investigated and suitable sub-synchronous damping controller is proposed and designed for one STATCOM that is located in common bus. Besides SSR damping, the STATCOM which is implemented in the transformer bus, can improve voltage stability and dynamical events such as power oscillations and first swing stability. Thus a shunt compensation using STATCOM in the transformer bus is a suitable complementary for passive series compensated transmission lines. Eigenvalues analyses carried out to verify the excellent performance of the proposed controller in SSR damping in seri Key Words: Sub-Synchronous Resonance (SSR), STATCOM, Damping Control.
