what can makes a generator vibrate more as load decreases
what can makes a generator vibrate more as load decreases
(OP)
I have a 45MWh generator that's showing a 3 mills of vibration ampliture when operating below 8MWh. The vibration will reduce to 1.2 Mills as soon as power production exceeds 8MWh.
It's clean to my mind that torque produce by the Prime mover(steam turbine) will increase the load angle and subsequently the Power being produced in the Generator Stator.
Since the frequency on the generator is constant at 60Hz(3600RPM) why the more vibration is produced at lower load (lower power production)?
Thank you all for your contributions.
M.D.
It's clean to my mind that torque produce by the Prime mover(steam turbine) will increase the load angle and subsequently the Power being produced in the Generator Stator.
Since the frequency on the generator is constant at 60Hz(3600RPM) why the more vibration is produced at lower load (lower power production)?
Thank you all for your contributions.
M.D.





RE: what can makes a generator vibrate more as load decreases
20% is getting fairly low for a steam turbine so is it possible the increase is coming from turbine crosseffects
Is this phenomina something new, then maybe a field short has developed (making the rotor thermally sensitive) and just by luck the thermal vector is opossite the the unbalance vector
RE: what can makes a generator vibrate more as load decreases
Thank you for your kind answer. I don't understand the full extend of your response... It's seems like you pointing out a thermal sensitivity of a field? (Magnetic? Electric?).
Temperatures in the generator bearing are very low (below 60C). Do you still believe that "thermal vector" will have such much effect?
Once again the question is:
Since the frequency on the generator is constant at 60Hz(3600RPM) why the more vibration is produced at lower load (lower power production)?
Kind regards,
M.D.
RE: what can makes a generator vibrate more as load decreases
RE: what can makes a generator vibrate more as load decreases
That's one possibility. I think most machines are supported well enough that change in torque load don't affect alignment, but you never know.
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(2B)+(2B)' ?
RE: what can makes a generator vibrate more as load decreases
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(2B)+(2B)' ?
RE: what can makes a generator vibrate more as load decreases
This is a real life situation involving persons of different backgrounds (operators, managers, engineers, acountants, technicians..).
Thank you for you kind responses... But a clear and insightfull explanation is still missing.
Here again is the question:
Since the frequency on the generator is constant at 60Hz(3600RPM) why the more vibration is produced at lower load (lower power production)?
This type of question will require to explain fundamental notion such as why Generator output (MWh) increase while the shaft (rotor) spins at constant synchronous speed (3600RPM).
So keep your contribution clear, simple and descriptive.
M.D.
RE: what can makes a generator vibrate more as load decreases
My scenario simplified is that the transmitted torque can make the stationary components move which can affect alignment, bearing loading, and vibration.
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(2B)+(2B)' ?
RE: what can makes a generator vibrate more as load decreases
The vibration amplitude (mills) is somewhat independent of the vibration frequency (60 Hz.). So in this case the speed is constant, but the amplitude of the vibration varies. The rotational speed of the machine in this has no case or effect with the change in the vibration.
RE: what can makes a generator vibrate more as load decreases
Look at oil lubrication pressures. The pressure area on the bearings will move with load. Are the bearing having a temperatuer change when the vibration is present? Make a temporary grounding rod with soft conductive material. you can either ground the shaft and see if it is decreased or measure or "look" for disturbances with an occiliscope of PQM. The aim would be to illiminate electrostatic influences.
RE: what can makes a generator vibrate more as load decreases
@djs (Electrical) In my case the vibration amplitude is inversely proportional to torque.
@ squeeky (Electrical) I'm glad you mentioned the Lubrication Pressure. I was thinking about the same idea... I will check it today.
Any other thought?
Sincere thank you to all contributor to this exchange.
M.D.
RE: what can makes a generator vibrate more as load decreases
We have a family of 6 turbine driven pumps that all act that way. They also tend to exhibit large changes in alignment with ambient temperature (driver and driven are oddly enough on separate support structures and see different thermal growth). When the bearing temperature goes up (indicating increase in bearing loading due to misalignment), the relative shaft displacement (mils) tends to go down.
The less likely part of my proposed scenario imo is the change in misalignment under load. Most (not all) well constructed machines and foundations/supports won't allow significant relative movement of movement of the two machines under torque load. It is more likely if driver/driven are independently supported or if the support structure from bearing to frame to foundation is weak or degraded.
New subject - Can you observe vibration response during a rapid change of MW loading? Rapid change of vibration would tend to rule out thermal-related factors while slow change would focus you back toward thermal factors.
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(2B)+(2B)' ?
RE: what can makes a generator vibrate more as load decreases
For that matter, any further vib data (orbit plots etc)?
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(2B)+(2B)' ?
RE: what can makes a generator vibrate more as load decreases
the most common effect of thermally sensitive rotor is that the unbalance vector caused by the unequal heating casues the vibration to increase, but, if your unit was balanced to negate a thermal bow at rated load, reducing field current will result in the balance weight correction actually cause unbalance at low load
RE: what can makes a generator vibrate more as load decreases
I was not directly involved so not know the details, bit i.e. when the drive was used in applications with comparable long idle times the gear was junk in 30% of its usual life.
My raccomendation here is more physcological, it is nice to explain the possible problems to everybody involved in understandable forms, but take care because managment will easily think that the solution is equally simple...
good luck!