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OLi

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Reply with quote  #76 
It was 39/76 if I remember correct generator is 1500 RPM, 25Hz, turbine 93Hz 5570 RPM.
I spent yesterday to measure 16 ch data from the machine including the movement of the hub axially during load and trips.
This is the largest turbine the OEM made so far and the only with this type of coupling, all other a little bit smaller tg sets run ok.
Damage are found in the coupling, independent consult report challenge if the teeth are equally distributed and if the tooth shape
levae the clearance that is required, nominally 0.3mm clearance should exist but as the report state, damage indicate that clearance do not exist in every case.
We have by measurement tried to check other alternatives such as shaft electrical current/voltage, it was max+-10mV on turning gear, +-50mV at 14MW load.
Torsion gave no indication from zebra tape test. Large (radial and tilt) movement generator/gbx are not found by laser measurement with fixtures from cold to 14MW including 1 night run at 3.5MW.
We have data from machine sensors on bearings and eddy probes and bearing sensors on gbx and turbine.
Coupling hub repeatedly suddenly move towards generator during steady state operation in steps 150 + 150 microns and suddenly 800 microns and the eddy probe at generator towards the coupling do suddenly at the same instant shift from having dominating 10 microns 60xRPM to 100-120 micron 2xRPM, 50 Hz and trip, also the absolute bearing sensor do the same up to as much 8-9 mm/s.
Yes, the coupling hub do vibrate at 12.5Hz, 0.5xRPM like 275 microns axially as it moves around at the same time.
In one case we have the sequence starting but reducing load 1MW make it stabilize and return to the low levels and load could be increased again w/o problem from 10MW to 14MW in a couple of steps and then it came back and tripped. So there are some indications that the coupling is involved. I will spend a couple of days trying to evaluate the data.


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John from PA

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Reply with quote  #77 
Quote:
Originally Posted by OLi
It was 39/76 if I remember correct generator is 1500 RPM, 25Hz, turbine 93Hz 5570 RPM.


76/39 = 1.949

5570/1500 = 3.71333

Problem obviously.

I calculate, based on the speed only the following possibilities:

Untitled.jpg 



OLi

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Reply with quote  #78 
In standard configuration the coupling can only as specified take 1mm axial movement and the last 2 runs this week it is made larger to take 3+ mm I think that is to little. I was not prepared for that and could not measure a gap of 1.5m with 1mm precision over time at this time. Generator housing and gbx case are radially stable relative each other, how the shafts behave nobody knows as they can't be seen. On generator shaft there are visible 3 lines and a reference that is max, min and nominal and they are within that range so generator is likely fixed at least also after going on grid. I will check the gbx number I got. Nominally in the catalog the coupling is referenced as a 1450RPM coupling it is now running at 1500RPM but that can't be a real problem? We can't find a root cause here and it is very frustrating and I am not that good on the inner secret life of this type of coupling and my view is that they should not be aligned perfectly as I find that give a shorter life by 50-75% as they wear very quick so that is my remaining reason for this event together with the for me unknown internal behavior if perfectly aligned. I am not sure I can make the OEM to move the machine off alignment just to test. Signature for a cardan shaft similar device that lock up is vibration at 2xRPM, well proven many times and what I think I see repeatedly here but it is just the reason for the trip not the cause. I have no better explaination. Why it lock up at random is the key question. I think the small versions of these that I am used to behave just like a large one that I see here but can be totally wrong.
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OLi

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Reply with quote  #79 
Sorry, my memory was wrong, it is given as 39/142 teeth and 1500 / 5470 RPM where 5470 may not be that exact as it is what control system measure. I will soon see what gearmesh I can find in the data. Another strange is that the turbine free end give vibration alarm like 5 min before generator vibration trip, maybe not every time but more than once. I will try to see what that is it is unlikely that anything unless connected to a torque impulse of some kind could trigger an event on the other end of the machine an deven then a few minutes delay is to long time I think, but may be wrong....
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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OLi

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Reply with quote  #80 
So my alignment expert says that these couplings are to be treated like a normal cardan shaft, no angle errors, parallell shafts but a offset that gives fredom for lube like 0.1 mm if you have a diameter like 500mm. Comments on that? 
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OLi

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Reply with quote  #81 
Find attached the FFT's from the trip at 14MW. It is really strange, we collect data every 11s on 16 channels and if you back 11s vibrations are lower and if you step 11s forward vibrations are lower so this is as close to the max we got. I sure learned a lot of things I never knew about this kind of coupling......

 
Attached Files
doc FFT diagram at trip BorĂ¥s R1573 appendix.doc (358.00 KB, 10 views)


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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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OLi

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Reply with quote  #82 
If you like a funny trend better, this is a relative probe axial on coupling hub during a 5MW trip.

Attached Images
png Start-4.2-MW-koppling-axial.png (47.39 KB, 13 views)
png Tripp-koppling-axial.png (44.39 KB, 12 views)


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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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OLi

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Reply with quote  #83 
Turbine oil is now in analysis, very thin light coloured almost like bio oil from corn or so, is that what they run on these days? No black oxidized look anyway but after like 100h operation it would be strange if it got black.
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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OLi

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Reply with quote  #84 
Oil was found ok almost as brand new, no varnishing, no oxidizing, as it should be after just a few hours use. Why discoloration in bearings? Could it be the blue paint after short run and normally you never see that before it is gone? OEM will replace coupling with something else so far not defined so we will see after the summer maybe.
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Danny Harvey

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Reply with quote  #85 
Thanks for keeping us posted.

This one is a real stumper. Good luck.
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