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A method for suppressing Subsynchronous Resonance (SSR) in large turbine-generators, as a result of series capacitor compensation of power systems, is presented. This method utilizes a thyristor-controlled phase-shifter to modulate the generator active power by injecting a quadrature phase voltage in the system. The rotor speed deviation from the synchronous speed is used as the control signal. An eigenvalue analysis and the complex torque coefficient methods are used to demonstrate the technical feasibility of a static phase-shifter for damping SSR. The analytical results are verified by a detailed digital computer study on the first IEEE benchmark for SSR studies, using the BPA's Electro-Magnetic Transients Program (EMTP). The simulation results indicate that injection of 2.4% of the system phase voltage in 4 steps of 0.6%, can suppress all torsional modes of the First IEEE benchmark model.