Abstract: During the trial operation of a 660 MW supercritical unit, the generator shaft and bearing vibrations rise abnormally during the loading stage. By tracking the changes in the generator bearing vibrations, a testing scheme is formulated and implemented. Based on the analysis on the operation and test data, the fault diagnosis on the generator bearing vibrations is conducted, which concludes that the thermal unbalance from the generator rotor coil asymmetric expansion causes the abnormal vibrations. According to the diagnostic result and by taking the site situation into account, counterweights are added to the low pressure Rotor 2 and the generator connecting wheel to carry out high speed dynamic balancing. The dynamic balancing results show that the generator bearing vibration is then effectively reduced with the turbine bearing vibration also kept in favorable range.

Key words: generator, vibration, thermal bending, dynamic balancing