StanBognatz
Mechanical
- Nov 1, 2005
- 16
I've got a unique situation with a recently re-stacked hydrogenerator. Vitals are:
# poles = 56 ; # stator slots = 360 ; line freq = 60 Hz ; rpm = 128.57
Old design had 4 stator core splits ; New design uses a continuous core stack
Vibration taken directly from the back of the core iron shows a 4.3 g-pk component at 720 Hz, with the next largest response at its first harmonic of 1440 Hz at 0.45 g. The adjacent keybar showed similar but slightly higher radial responses of 4.8 and 0.9 g-pk, respectively. Tangential responses on the keybar were 0.9 and 2.4 g, respectively.
Through each spectrum 120 Hz harmonics are present, but they are comparatively low level, typically 0.05 to 0.09 g.
The 720 Hz vibration creates significant audible noise, with levels that increase directly with load. At FSNL and with excitation on, we have about 75 dbA at 20' outside the generator enclosure. At 35MW load, we have 90+dB, with the predominant 720 Hz component.
Sister units to this problem unit operate at full load with noise levels in the 75 dBA range; no access for vibration measurements at this point.
Our client is not accepting the unit for operation based upon the noise being generated. We have had several theories regarding the source of the noise, with possible solution. But unfortunately, none of them has been very viable from an operational perspective.
I would appreciate any commentary on the issue.
Thanks,
Stan
# poles = 56 ; # stator slots = 360 ; line freq = 60 Hz ; rpm = 128.57
Old design had 4 stator core splits ; New design uses a continuous core stack
Vibration taken directly from the back of the core iron shows a 4.3 g-pk component at 720 Hz, with the next largest response at its first harmonic of 1440 Hz at 0.45 g. The adjacent keybar showed similar but slightly higher radial responses of 4.8 and 0.9 g-pk, respectively. Tangential responses on the keybar were 0.9 and 2.4 g, respectively.
Through each spectrum 120 Hz harmonics are present, but they are comparatively low level, typically 0.05 to 0.09 g.
The 720 Hz vibration creates significant audible noise, with levels that increase directly with load. At FSNL and with excitation on, we have about 75 dbA at 20' outside the generator enclosure. At 35MW load, we have 90+dB, with the predominant 720 Hz component.
Sister units to this problem unit operate at full load with noise levels in the 75 dBA range; no access for vibration measurements at this point.
Our client is not accepting the unit for operation based upon the noise being generated. We have had several theories regarding the source of the noise, with possible solution. But unfortunately, none of them has been very viable from an operational perspective.
I would appreciate any commentary on the issue.
Thanks,
Stan
