PLEASE FIND ATTACHED FILE
I HAD ATTACHED FILE THAT SHOWS ORBIT PLOTS OF GAS TURBINE
PLEASE CHECK AND GIVE ME YOUR FEED BACK.

ORBIT_PLOT.xls (130 Kb, 110 downloads)

There is definitely something wrong with the machine. Either severe rub , looseness or rotor instability. If possible, try to achieve average rotor centerline plot and superimpose orbit plot on the average centerline plot. May give a more clear picture.
Regards.
IRSHAD AKHTAR

Quote:"There is definitely something wrong with the machine. Either severe rub , looseness or rotor instability" - This statement is nonsense: none of the data shown provides any evidence for these claims


I don't know what your concerns are, but there's nothing in the data to suggest any worries about the machine health.

The vibration at both ends of the machine contains significant amounts of runout or glitch.

At 5830rpm, API suggests an allowable level of 36 microns p-p with 9 microns p-p of runout.

At the NDE there is 1X of 3 microns and 10 microns overall, so nothing to worry about there.

At the DE, 1X is 10 microns and overall is 19 microns again nothing to worry about.

It would be more meaningful if you considered displaying 1X compensated orbits from the System 1 as a better indication. Compare 1X compensated and uncompenstaed data in bode and polar formats to judge balance condition.

With this proportion of glitch in the signal, if you look at spectrum plots you will see a tiny 1X component followed by many harmonics.

Try looking at a cascade plot to see how the runout/glitch content stays constant.

What is the history of this machine:

Is it new?
Are there contractual issues with v ibration/glitch levels?

Has System 1 just been fitted and you are seeing this behaviour for the 1st time?

Has this glitch just appeared after maintenance?

This message has been edited. Last edited by: Buzz LightYear,

Buzz is exactly correct (as usual). There is nothing wrong here except some glitch on the unfiltered signal.

Nevermind

Can not call my self an expert, but what about reverse precession apparent from the both plots?

I would be hesitant to call anything on data so heavily influenced by glitch.

The DE unfiltered data shows that the X probe is 'seeing' the peak before the Y probe, suggesting a possible labelling issue - crossed probes or wrong direction of rotation.

For a rub to produce reverse precession it has to be quite heavy, resulting in a non-steady 1X amplitude and phase.

Unless the OP can produce more data or indicate his cause for concern, anything other than a statement that the data is mostly glitch is just speculation.

Although reverse precession is apparent in one of the two filtered orbits, and barely discernible in the other, it likely is too soon to be certain of the actual precession. First of all the wiring should be verified as to convention (loop test) and then data reacquired and properly compensated. Gas turbine probe conventions can be significantly different and frequently cause apparent reverse precession.

Reverse precession is often considered to be a symptom of a rub but typically this type of rub exhibits quite large amplitudes, something not evident here as pointed out by some austute individuals.

John from PA

The probes are probably configured backwards. That is the most common cause of reverse precession.

But at 3 microns, I have seen the glitch add to the signal in such a way to make the precession appear to be reverse. Matter of signal to noise ratio being just right...