3.1 Torsional Stimulus Types

Electrical turbomachinery is subject to the most varied and often most severe torsional disturbances in comparison to other machinery classes. In particular, turbine-generators used to develop power for utility and industrial applications require great attention at the design stage to torsional vibration to avoid operational problems from electrical events that produce pulsating torques on the generator rotor and stator. These complicated machines involve several rotors that may include a steam turbine, a gas turbine, or both types of rotor elements coupled in tandem to the generator rotor. This book focuses on application examples of this class of machinery because other machines are often a simpler subset.

Figure 3.1 shows a large steam turbine-generator having several steam turbine elements connected in tandem for driving the generator. These machines are enormous in size, with individual rotors weighing several hundred tons in many cases. The enormity of these assembled machines may be judged by comparing the size of the machine to the people in the background of this photograph.

Figure 3.1: Steam turbine-generator. (Courtesy of General Electric.)

For turbine-generators there are a wide variety of planned and unplanned incidents that can cause electrical current oscillations in the transmission equipment to which the generator is connected at its terminals.4 In each case, the incidents result in an oscillating torque applied to the generator rotor, which can stimulate twisting oscillations in the machine shafts and vibration of various rotating and nonrotating components.

3.2 Transient Disturbances and Vibration Response

Transient disturbances...