Justification of torque per unit velocity methods of analyzing subsynchronous resonance and a swing mode in power systems

Torque per unit velocity is a practical method to study the subsynchronous resonance instability of electric power systems. The torque per unit velocity method is justified as an eigenvalue perturbation technique and extended to power systems with thyristor switching devices and multiple torsional modes. A new method to estimate the damping of the swing mode is proposed.