VARIATION OF TURBOGENERATOR STATOR CORE VIBRATION WITH LOAD

The Maxwell stress equations are used to determine the distribution of electromagnetic forces at the surface of the stator bore for the dual purpose of investigating the cause of the observed variation of double frequency stator core vibration with load and power factor, and of providing the basis for supplying information about the current status of this vibration to an online bearing monitoring program. The main cause of the change in vibration with load is the way in which the radial and circumferential stress distributions combine in space and time. However, magnetic saturation of the iron is also highly significant, and so a scheme to incorporate this nonlinear effect into an intrinsically linear model is developed. Calculation of the actual vibration level of a given machine depends on two structural finite-element analyses, the first yielding the transfer coefficient linking radial force to radial vibration, and the second the coefficient linking circumferential force to radial vibration.