Modal analysis of the inner cover of a ۴۵ MW generator

This paper investigates the design and modal sensitivity analysis of the inner cover of a special generator ۴۵ MW. The inner cover is the last component assembled on the generator's stator, and its role is prevention from ingress of external elements into the generator. There is no need to stress analysis of the inner cover as this component doesn't carry any external mechanical loads. Such parts that don't take any mechanical load(s) fabricate from composite materials with low density and high Young’s modulus. In the generators, the effect of the rotor unbalance load has a high magnitude and is not ignorable. It has an important impact on all other stationary components because it applies a harmonic load with a ۵۰ Hz frequency. So, this force (unbalance) is the excitation load, and it transmits from bearings to the frame or base frame of the generator. If any equipment or generator components have a natural frequency range between ۴۵ to ۵۵ Hz, they will vibrate during the work cycles. Permanent vibration of any component of an integrated system causes damage due to the vibration fatigue (the failure of bolts and other fasteners are examples of this problem). Hence, manufacturers should investigate the modal properties and behavior of all components. In this case, as mentioned, the excitation load applies with ۵۰ Hz frequency, so we want to check the natural frequencies of the inner cover set in assembled mode on the frame of the generator. In the post-processing step, if the natural frequencies of the inner cover are close to the frequency of the excitation load (۵۰ Hz), we change it with geometrical modifications and keep the margin of the natural frequencies of the inner cover set, at least ۵ Hz (۱۰%) from the excitation force frequency. Finally, the results of the finite element method will be compared with the experimental results for a segment of the inner cover.

کلیدواژه ها:

inner cover ، vibration analysis ، experimental modal analysis ، finite element method ، sensitivity analysis