×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Generator Vibration

Generator Vibration

Generator Vibration

(OP)
Hello,
I first want to say thank you in advance for those who help.
I need your advise for the following problem
Generator (10 MW and 6600 volt)coupled to gas turbine via gear box.
we make re winding for the generator stator winding and after generator operation it have high vibration reading (after vibration analysis unbalance is found on rotor shaft)
BUT
after 4 months of continuous operation the vibration reading backs to its normal !!
also, after stopping the generator for two hours and start it again the vibration readings become more high again !!
Why the vibration decreased and increased again ???

RE: Generator Vibration

The possibilities are wide open. Ideally you'd like to compare everything you can about the conditions under which vibration occurred and when it didn't occur (loading, excitation, temperature).

You mentioin unbalance so I gather the vibration is 1x. Some sources of 1x that can change with conditions:

1 - thermal bow of rotor can cause vibration to get worse as temperature increases. If this is trim balanced based on balance conducted at high temperature, the vibration may be higher at low temp and lower at high temp. Or there may be a compromise balance attempted.

2 - Shorted rotor turn can cause something resembling a thermal unbalance that may be sensitive to rotor excitation level (and time since excitation was applied).

3 - Thermal changes can affect supporting structures causing misalignment which causes 1x vibration.

4 - Bearing oil and seal oil temperature changes can dramatically change characteristics (stiffness) of bearings and seals which can tune resonances toward/away from running speed.

That's all that comes to mind at the moment but I'm sure there are more possibilities. But again the best approach is probably to start with the known facts about what conditions changed and work from there. Also more details about the vibration might provide some clues (did it affect all bearings, was it directional, purely 1x, separate measurements of bearing housing and shaft relative vib, etc).


=====================================
(2B)+(2B)' ?

RE: Generator Vibration

In addition to the suggestions from electricpete - has anything changed for shaft earthing? It is Gas Turbine Generator - so i believe one bearing is insulated and shaft earthing is provided. Is there any change in shaft grounding brushes or currents?

Have experienced similar problem for steam turbines of quite bigger size. We determined root case was grounding.

NC

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources