Damping estimates of subsynchronous and power swing oscillations in power systems with thyristor switching devices

The authors extend the torque per unit velocity method for estimating the modal damping of subsynchronous oscillations to general power systems with thyristor switching devices. This allows damping of SSR by thyristor controlled series capacitors to be obtained from time domain simulations of only the electrical part of the system. Their method generalizes to the case of multiple torsional modes with the same natural frequency. A new method is used to estimate the damping and frequency of the swing mode. Torque per unit velocity methods are easier than exact eigenvalue analysis and testing on the IEEE first benchmark SSR model shows excellent agreement with exact eigenvalue analysis.