We have a GE Frame 9E unit. Generator Turbine End bearing proximity vibration increases during evening hours and decreases during early morning, while MW load remains constant. All other turbine and generator bearing vibrations remain stable. Has anyone experienced similar behavior? Any recommendations on parameters to trend would be appreciated.

 

@ammadali019,

There are a LOT of question below--because there are a lot of factors which can affect generator vibration, and we don't have any idea what might be causing or contributing to the problem(s). The intent of the questions IS NOT to overwhelm anyone with requests for information, but rather to cause those persons on site to consider and investigate these factors asked in the questions below as they try to troubleshoot and resolve the issue.

By how much does the proximity vibration increase?

Are there any alarms on the vibration monitor the proximity probes are connected to indicate problems with the proximity probe or proximity probe power supply?

When did this problem start? After a maintenance outage? If so, what work was done in the Load Compartment or on the generator during the maintenance outage?

Have there been any changes in turbine-end generator bearing metal temperatures or bearing drain temperatures lately? Do they change when the proximity vibration increases?

What is the reactive power (MVAr) doing during the day, specifically when the vibration is changing?

What is the generator output voltage doing during the day? If it's changing, by how much during the time during the increased vibration period?

Is the generator hydrogen-cooled or air-cooled? If it's hydrogen-cooled, is there any change in the cooling water temperature entering the hydrogen-to-water coolers?

If the generator is hydrogen-cooled, is the hydrogen pressure varying during the day/night? If so, by how much?

When you say proximity vibration is increasing, it's presumed you are referring to Bently-Nevada proximity probes--or similarly styled distance measuring probes?

Is one or both proximity probes indicating increased vibration?

What are the velocity vibration probes on the turbine-end generator bearing indicating during the day? Are they working correctly?

It's presumed the Load Compartment is cooled by a vent fan or fans. Is the ventilation system working properly? Is the temperature in the Load Compartment changing? If so, is it getting cooler during the evening/night hours and warming during the daylight hours?

Is the machine running at Base Load, or Part Load (possibly using Pre-Selected Load Control)?

Is the machine using VAr/pf (VAr/power factor control) during the period when vibration appears to be increasing? If so, how much does the MVAr reading (and generator terminal voltage) change during the period when vibration appears to be increasing?

Generator vibration--any vibration--IS NOT controlled by either the turbine control system OR the proximity vibration detection system. Yes; if MVAr/pf control is enabled and active, the turbine control system is varying generator field excitation to maintain either a MVAr or pf setpoint, but that's not controlling vibration. There have been situations where changes in generator excitation have cause increased vibration, usually do to some looseness or problem with generator field blocking or loose end turns and/or increased field heating due to increased generator excitation. BUT, these are all mechanical problems--not controls-related problems.

The control system/vibration monitor is only "reporting" what it's receiving. BUT, vibration is strictly a monitored condition, not a controlled condition. The vibration can be "triggered" by changes in generator field excitation, generator cooling, Load Compartment cooling, grid conditions (large changes in grid voltage that result in large MVAr changes and/or large generator excitation changes, but the control system/vibration monitor is only reporting vibration and/or changes in vibration. It's either the probes, probe adjustments, proximity probes, vibration monitor card/component issues or changes in actual, real, physical vibration that have some possible stimulus/trigger due to actions the control system is doing in response to operator or grid conditions.

The good news about proximity vibration measurement is that it can be very easily used to analyze and help pinpoint the cause of vibration, as opposed to seismic vibration probes which can't really provide much in the way of diagnostic information. It is strongly recommended if the indicated proximity vibration readings started suddenly and without any obvious mechanical or operational changes (load; MVAr; pf; generator excitation; turbine-end bearing metal temperature or bearing drain temperature) that a qualified representative knowledgeable in analyzing machine proximity vibration readings be invited to the site to assist with determining what might be happening.

Please use the above questions to help analyze and troubleshoot the issue and if you arrive at a resolution please write o let us know what you find.