Tuning the ratio of KGEN-LP/HGEN to suppress vibrations of turbine blades

This paper proposes a new approach to evaluate the torque responses of turbine shafts and blades induced by power system faults. Based on electromechanical analogy, a turbine mechanical system can be transformed into an equivalent circuit and be analyzed easily from the phasor diagram. It is found from the analysis results that the shaft-to-rotor impedance ratios govern the torque response of turbine blades due to the system-frequency excitation. Particularly, the one relating to ratio of KGEN-LP to HGEN, or the Generator/LP-turbine shaft stiffness coefficient to the Generator rotor inertia constant, governs the vibrating behaviors of all blades. Therefore, it is proposed that tuning this ratio to make the blades intrinsically less responsive to electrical disturbances. As a result, the designer can more efficiently design the blades without too much limitation in structure space and strength. From the simulation results, it has proven that the proposed method actually suppresses the torque vibrations of blades to acceptable levels.