Posted on behalf of Sanjeex Sharma
sanjee_sharma@hotmail.com

We at our Power Station have a Primary air fan motor( 6.6 Kv) having high vibrations problem.The motor is 1250 KW and rotating speed is 1485 RPM.It has journal(white metal) bearings.The fan is overhung type and draws primary air from atmosphere.

The motor appears to have the phenomenon of beats as the vibrations are not steady and are periodic in nature.

The phase analysis indicates rocking of bearing pedastal as there is a phase revarsal of 180 degrees across the pedestal.(180 degrees phase difference on the two legs of the pedastal).This phenomenon is there on both motor bearings but not on the fan side.This phase difference is getting carried to the base plate too.

Also the vibrations are within limits on the fan bearing housing.Phase analysis indicates no misalignment across the coupling.

Kindly go through the case and advise probable cause.

Posted on behalf of Sanjeex Sharma
sanjee_sharma@hotmail.com