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Torsional interactions encountered with series compensated transmission lines are due to the negative damping effect of subsynchronous frequency currents induced by rotor oscillations. Methods of controlling these currents have appeared in the literature, however, this paper offers an alternative scheme based on enhancing the supersynchronous currents associated with positive damping. This results in cancellation of the negative electrical damping at the mechanical resonant frequency. The countermeasure consists of a passive shunt device connected at the generator terminals and tuned to the proper resonant frequency. The operating principle and design considerations are discussed and the effectiveness of the scheme is demonstrated.
Date of Publication: March 1986