Sensitivity of Subsynchronous Resonance Predictions to Turbo-Generator Modal Parameter Values and to Omitting Certain Active Subsynchronous Modes

In a subsynchronous resonance stability stuiy the predicted CRITICAL COMPENSATION LEVEL (CCL) depends on the mathematical model and parameter values, particularly on the mechanical damping or decrement factor. Measurements of the mechanical parameters yield values for modal inertia, modal damping etc. so that the mechanical system equations have to be transformed into modal form in order to use the measured data in simulation studies. This paper investigates the sensitivity of the predicted CCL values (for a particular case study) to uncertainties in the different modal parametes and finds that the modal damping or decrement factor is more critical than modal inertia or mode shape. It carries on to show how the modal model can be reduced from 12th to 4th order and still yield acceptable results; this would lead to considerable simplfication and saving of computer time in multi-machine SSR studies.