Can the forum advise on vibration data from a Solar Gas Generator? There is an increased level at the mid journal bearing to 56 microns, there is a similar amplitude at the other probe. These levels have increased steadily over recent months, although they are still not in alarm on the Bently (3300 series) panel (65 microns = 1st alarm). The data indicates a frequency of 175 Hz as the principle component (I presume this is 1x, but cannot quantify this as the local panel gives speed as a percentage and not as RPM). The Power Turbine has a frequency component of 129 Hz (again the N2 speed is expressed as a percentage)and the compressor has a speed of 10075 RPM (168 Hz). The GG amplitude has increased from an average of 24 microns earlier this year. I think that there is an impending problem here, but a) How to quantify this and b) How best to proceed? Any thoughts on this from the board would be appreciated.
Thanks, Steve

Normally you can find the power turbine speed by back tracking from the compressor speed and also the gearbox ratio. On the question on quantifying the GP speed, I guess you could refer to the manuals on the rated speed of the engine and calculate the estimated speed based on the percentage of the speed. (Well, that's what I do normally )... Maybe you can post a few vibration spectrums?

Is there a keyphasor associated with each unit in the machinery train, what is this unit driving, is there a gearbox involved. If there is a keyphasor you can derive the speed with a time waveform from each keyphasor. What type of solar is it Mars or Taurus or what.

Steve,

Based on the info you've given, it seems like GG fouling maybe causing the rise in vibration level. But, then again, I am sure these units undergo detergent wash as a routine PM, to ensure the fouling is kept at bay...Is this being done? When was the last wash done? Other things to look out for are deviations in PCD, T5 and lubricant properties, all of which will support or negate fouling/unbalance phenomenon.
Also, you need to back track if the change in amplitude over the months, is purely occuring at running speed.....More data/spectra is required to better understand the vibration dynamics.


Cheers...Rajan Muthukrishnan

This message has been edited. Last edited by: RajSha,

First may you give the total hours of your machine, your problem is not out of 3 guesses: mechanical or aerodynamic unbalnce or shaft bending, you need to checck the phase , I have a GG equiped with BN 3500 rack and has a key phasor, once have a 1X peak and permanent phase, unblance is existing.May you a BN snap shot device from your boss, plug it in 3300 and figure it out.

Thanks for the replies.
The GG is washed on a PM, the last was completed on 23rd Sept and has a frequency of every 1500 hrs. However, the trend indicates a longer period of time of increasing vibration. Have attached some data to preview, trend, spectra & gap volts.
There is an indication of a slight increase in T5 but no change in PCD

GG.doc (56 Kb, 11 downloads)

Steve,

Not sure what slight increase in T5 means but, if this does not correspond with change in PCD then, there is no concern of fouling of the GG. However, the vibration trend you posted seem to indicate unusual fluctuation up until the first quarter of this year...like something is sticking or if it corresponds to the timing of GG wash then it may have some significance. Do you have RTD on this bearing...how does the temperature respond? Do you know what the initial gap voltage setting is on these probes?

Cheers...Rajan Muthukrishnan