Dynamical stability of synchronous generators under torsional interaction

It is known that three completely different aspects, i.e., induction generator effect, torsional interaction and transient torque, are concerned in subsynchronous resonance of a power system. Both electrical and mechanical dynamic processes are involved in torsional interaction, and there exist both electrical and mechanical self excitation. Practically, it is very difficult to separate the induction generator effect from the torsional interaction. Generally, torsional interaction will play the main role when the frequency of the subsynchronous alternating torque approaches any one of the natural frequencies of torsional vibration. On basis of the time-domain technique of perturbation analysis, the torsional interaction has been studied. With the time domain method, the force-free or transient component caused by the system itself can be taken into account besides the forced component of the oscillation. As the product of the increments is not neglected in the perturbation analysis, the interactions between every component of oscillation are also considered