2.1 Definitions

damping coefficient The damping coefficient C, when multiplied by vibration velocity (the first time derivative of ? in rad/s), produces damping torque. The unit for the damping coefficient is lbf in s/rad or N m s/rad in U.S. Customary and SI units, respectively. algebra is given in App. D for readers who need it for reviewing the sections on vibration theory in detail.

electrical transmission system frequency The electrical transmission system frequency in the United States is 60 Hz. In some other countries it is 50 Hz. The terms subsynchronous and supersynchronous refer to frequencies below and above the transmission system frequency, respectively. In the application examples in this book it is assumed that the transmission system frequency is 60 Hz when using the terms subsynchronous and supersynchronous. Subsynchronous resonance (SSR) refers to a torsional instability caused by powerful interaction of turbine-generation torsional vibrations and current oscillations in the electrical network and generator, at frequencies below the transmission system frequency (60 Hz in the United States). algebra is given in App. D for readers who need it for reviewing the sections on vibration theory in detail.

endurance limit The endurance limit or high cycle fatigue limit is a property of some materials. If the alternating stress falls below this limit, in theory an infinite number of fatigue cycles can be sustained without initiation of a fatigue crack. High cycle fatigue is associated with cyclic strain levels for...