Depressing the torque vibrations of turbine blades using virtual inertia

Based on an electromechanical analogy, a turbine mechanical system can be transferred into an equivalent electrical circuit, allowing a phasor diagram to be used to evaluate the turbine shaft and blade responses to the electromagnetic (E/M) torque disturbance. After investigating six practical large-scale turbine units using frequency scanning, the dynamics of the blades were always found to be sensitive to system frequency excitation. Therefore, a system-frequency mechanical filter was designed and installed in the generator-and-rectifier section of the turbine set. This filter normally operates in a non-resonant state with only a low inertia constant such that the system operation is not affected. Only in the event of a fault, does the filter resonate and produce an extremely large virtual inertia that combined with the generator-rotor inertia to make the turbine system, especially the blades, less responsive to the system-frequency E/M torque disturbance. Using simulations, such a virtual inertia was proven to present excellent performance in improving the blade vibration behaviors. (C) 2002 Elsevier Science B.V. All rights reserved.