While vibrations as measured on the casing were significant
particularly for Units 2 and 3, these levels were not of major concern.
Vibration frequency spectrum under steady-state operation
showed dominant spectral peaks at 25 Hz (corresponding to the
generator 1¥ RPM synchronous frequency) and 250 Hz (turbine 1¥
RPM rotation frequency). The other significant spectral peak was
at 460 Hz (1¥ gear mesh frequency). The second harmonics (50 Hz)
of the generator 1¥ RPM synchronous frequency was insignificant
(noted primarily on the generator casing measurements only). This
50-Hz component corresponded to the electrical line frequency of
50 Hz. The other notable peak (occasionally noted in the spectrum)
was 225 Hz (9¥ generator RPM or the lower sideband of the turbine
1¥ RPM of 250 Hz modulated at the generator RPM).