Dynamic Instability of a Turbine Generator due to Microslip

Abstract

The present paper is concerned with dynamic instability of a turbine generator due to friction between rotor slot wedges and the rotor. When the normal force on the wedge is constant the dissipated energy is of the same type as hysteretic material damping in the sense that for a circular motion excluding gravity it is independent of the rotational frequency, but changes sign when the rotational frequency exceeds the vibrational frequency. The magnitude of the dissipated energy will however depend on the rotational frequency as the normal force does. The transferred energy due to friction is a nonlinear phenomenon and approximately proportional to the amplitude cubed and may be much larger than material damping. It is also shown that when gravity is included or the motion is elliptical the energy transferred is larger than for a simple circular motion.