Damping of commonmode torsional oscillations using a modified NGH SSR damping scheme

This paper presents the analyzed results on the application of a modified NGH SSR damping scheme for damping commonmode torsional oscillations that occur in a power systems containing seriescapacitor compensation. The IEEE Second Benchmark Model, system2, which has two nonidentical turbinegenerator sets connected to an infinite bits through a seriescapacitor compensated transmission line, is employed to investigate the possible unstable subsynchronoiis resonance (SSR) which can be suppressed by the proposed damping scheme. A unified approach based on modal control theory is employed to design damping controllers for the modified NGH SSR damping module. Frequencydomain approach based on eigenvalue analyses such as different operating conditions and stable regions on R_EX_C plane is performed. Timedomain approach based on nonlinear model simulations under a severe threephase shortcircuit fault at infinite bits is also carried out. It can be concluded from the simulation results that the proposed modified NGH SSR damping scheme incorporated with the designed damping controllers can effectively suppress the commonmode torsional oscillations.