Hi, Got some vibration data in one of the ID Fan assembly, Motor is a 2 pole motor connected to the fan through spring-grid type coupling. Max speed 3000 rpm. The fan is not able to go to full speed due to high vibrations, its a VFD system (variable frequency drive). I did not see any predominant 1X freq component. More no. of multiple harmonics are seen in the spectral data
I was able to take the data at 1500, 1800, 1920 and 2100 rpm. I noticed a strange behavior in the system. The vibration signatures shows multiple harmonics. Could not see any bearing defect frequencies. On day-1 when I took the data at 2100 rpm all vibs were in limits. When I took the vib data on day-2 at 2100 rpm all vibs went up by 3-4 times on Fan DE and Fan NDE bearings.
Vib data, corresponding comparative vib signatures are provided in the attachment. Is the spring-grid type coupling the culprit...???
Any kind of inputs are welcome