Replacing the Packing of Generator Bearing

Control Gent's,

I hope this message finds you all well.

We have replaced the packing of the Generator Bearing by a standard one supplied by OEM. We tried to start-up the turbine 3 times and it tripped due to high vibration on generator DE and NDE. It seems that the packing is tight or not installed well. Every time, turbine trips on higher speed (3,500 - 3,900 - 4,100 / rated speed is 5,100 rpm).

Can anyone share the right procedure for packing replacement ? and what is the recommendation for start-up trials ?

Generator is 25MW Holec Generator driven by GE Frame 5
Bearing is RENK EMXLB 28-335


Thank you in advance.

As you have noted, we are control gentlemen--heavy emphasis on gentle. This question (how to replace generator bearing packing) is not really related to controls.

The generator manufacturer should have provided a manual of some sort, usually even a parts list drawing will provide dimension checks which must be made when installing a bearing to make sure there is no rubbing of the "packing" or seals which can result in damage and/or excessive vibration.

It's not clear if the photo was taken before the new parts were installed or after the high vibration was discovered. If the bearing caps were opened after the replacements and the tripping incidents was any abnormal wear of the seals and "packing" or rotor shaft noted to indicate the problem is caused by the new components or improper installation?

Has anyone been near the generator to say if the vibration is real, or if it is possibly a problem with the instrumentation?

What kind of vibration sensors are in use in the generator bearings? Seismic (Velocity) sensors (pick-ups)? Proximity sensors (possibly made by or similar to those made Bently-Nevada)?

If someone standing near the generator when the START attempts were made and did in fact feel excessive vibration then at least two things are wrong. If no excessive vibration was felt by someone standing near the generator during multiple START attempts then it would seem there is some kind of vibration sensor (pick-up; probe; wiring) problem. To remove the bearing caps the vibration sensors had to be disconnected and removed and re-instaled and re-connected. Or maybe even replaced with new sensors which had a different sensitivity or were not installed properly and are causing erroneous vibration signals. If excessive vibration was felt by someone standing near the generator during multiple START attempts then the it's very likely some damage has occurred to the generator and the new seals and "packing."

It's common after mechanical work like this has been done to have at least one person standing near the equipment to listen for rubs and watch for other problems (oil leaks) and sense unusual or excessive vibration. That person, or persons, should be stationed in the area until some time after reaching full speed and even part load, and should return to check for any issues repeatedly after such work to try to avoid any serious damage which might result from the work performed or the components installed. And repeated START attempts after high vibration trips without verifying the actual presence of vibration after the first trip and/or confirming the vibration sensors are all working properly and were re-installed and re-connected properly before attempting even a second START could lead to damage that could have been prevented.
We do, from time to time, go into mechanical issues when it's related to controls issues, but instructions and/or procedures for installing bearing seals and "packing" are outside our normal discussions here on

Please write back with more information (type of vibration sensors; what work was done to verify the vibration sensors are connected and working properly; have actual high vibrations been humanly observed or proven to exist by some other instrumentation; etc.). And to let us know how the issue was resolved.

Finally, the generator rotor had better not be spinning at the speeds you mentioned.... Those are turbine shaft speeds and there is a reduction gear (often called a load gear) between the turbine and generator to reduce the speed of the turbine shaft to 3000 RPM for the generator to be able to produce 50 Hz AC (Alternating Current). It's most common to speak of turbine--and generator--shaft speeds in percent of rated speed since when the turbine shaft is at 50% of rated speed the generator rotor is also at 50% of its rated speed, and when the turbine shaft is at 80% of rated speed the generator rotor is also at 80% of its rated speed.