3 M.W Steam Turbine Vibration Problem

What is the recent history involving work on the machine?  The amplitude seems to be quite load sensitive and the largest amplitude changes at the coupled ends of the machine.  Has anything recently been done that would affect alignment? 

What type of coupling and method of lubrication is used between the turbine and generator?  

 

I support the above posts.

To verify the possibility of alignment,  you may like you measure the phase angles. Can you collect orbit plots? Bode plot?

The plots you posted look like taken by a CSI device.  This device is able to collect both angles and orbits.

Regards- Ali M. Al-Shurafa

Kishore kumar posted:

Dear Members ,

We have observed increase in  3 M.W vibration trending running at speed 3000 r.p.m .Please refer the below attached spectrum and share your analysis .

I noticed on your plots that the names of the points are different. The turbine's points are defined as "X" and "Y while the generator points are defined as "Horizontal" and "Vertical", which indicates maybe the generator data is taken on the bearing housing.

Does the generator have sleeve bearing with no prox probes, or does it have anti friction bearings?

Ralph Stewart posted:
I noticed on your plots that the names of the points are different. The turbine's points are defined as "X" and "Y while the generator points are defined as "Horizontal" and "Vertical", which indicates maybe the generator data is taken on the bearing housing.

Does the generator have sleeve bearing with no prox probes, or does it have anti friction bearings?

Ralph, first of all the machine has a nominal rating of 3 MW, the equivalent of slightly over 4000 HP so it almost certainly does not utilize rolling element bearings.  Additionally all plots are in units of P-P Displacement in Microns so I'd bet all the plots are from proximity probe signals.

As far as "X" and "Y" and "Horizontal" and "Vertical", if the BN convention is followed, and it likely is, "X" is associated with "Horizontal" and "Y" is associated with "Vertical".  Many years ago BN rack channels were identified horizontal and vertical because a key diagnostic instrument was the oscilloscope which also had horizontal and vertical channel inputs.  These days "diagnosticians " are likely not to know how to use an oscilloscope.  How the channels are ultimately identified when plotted may be a result of an OEM naming convention or a knowledgeable individual setting up a rack or associated monitoring equipment to the BN convention.

We have taken readings on casing at journal bearing  area with csi2115. And the turbine direct coupled  to its alternator.

This turbine is just a year old. No history of any repairs. What about oil whirl problem ?. Because the oil temperature is maintaining  46 Deg while entering & 65 Deg while returning. 

And there is a peak before 1 X. We dont have facility to take orbit plots now. 

Please share your opinion. 

 

CSI 2115 can take phase. Do you have a key phasor on the machine?

Even if the machine is relatively new, there could be problems and as an analyst I would avoid eliminating possible causes based on limited data. If I were you I would review the commissioning reports including the alignment and thermal growth details.

 

Can you share the trends for the vibration as it Increases? 

Oil whil/whip come at around 0.4X and typically the amplitude is high. Do you see these symptoms in other plots?

Regards- Ali M. Al-Shurafa 

I am a third party engineer, already i made a discussion on alignment and the data taken while commission . Some other  company engineer attended till aug2017. 

Vibrations trending 15 to 20 microns since august ar 3000 r. p. m, 2M. W load. 

Turbine made by china  company, so that i advised to contact them for clarification. 

I think it unfortunate that you don't have some proximity probes and a keyphasor, and perhaps that is a lesson for the future.  But based on the limited data I would be inclined to check the alignment.  One additional thing I would check, and prior to or part of the alignment process, would be the condition of the sliding key at the front standard of the turbine.  Generally there is some recommended maintenance in that particular area to insure that the turbine casing can expand/contract and not develop any distortion issues.  Check to see what recommendations the OEM has with respect to the key; usually there are some lubricant recommendations.

Following on John's comment, you can measure the thermal growth as part of the check he suggests for the key. 

One item that can cause such trouble is improperly fitted thermal insulation.  A visual inspection and thermal pictures can be used for this.

Don't forget the piping design.  Thermal growth of the piping can relate to such issues.

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