We have some turbine generator (12 MW) system vibration problem. Thus happen in unussual frequency 0.75x operating speed (opr speed = 3000 rpm). The vibration start to rise when we put some load to the generator, we can operate the generator until 2.5 MW without significant vibration at 0.75x (about 3 microns) but when we put more load thus vibration could jump suddenly and stopped the turbine. Please let me know if you have some experience on this or another typical problem.

Tanya – Satch Js

Dear All,

We have some turbine generator (12 MW) system vibration problem. Thus happen in unussual frequency 0.75x operating speed (opr speed = 3000 rpm). The vibration start to rise when we put some load to the generator, we can operate the generator until 2.5 MW without significant vibration at 0.75x (about 3 microns) but when we put more load thus vibration could jump suddenly and stopped the turbine. Please let me know if you have some experience on this or another typical problem. Thx.

Tanggapan 1 – yoki vriandana

Did the vibration at 0.75x followed by its harmonics or just significant in one direction or other related ..?I think it need more information about this….thanks.

Tanggapan 2 – JONO

Dear Satch,

You gave more load and your turbine vibrate also more, this is common for a thermal bow problem. Which one the proximity showing 0.75x OS ? Could you share your orbit? bode?

Tanggapan 3 – Satch Js

Dear All,

Thank you for your kind response. Ok our turbine is directly coupled steam turbine made by Turbodyne. It runs at 3000 rpm. Before this high vibration problem we do have a problem with our gear coupling which is indicated by high vibration at 1x frequency in Inboard Turbine. But since last week when we try to adjust the load we found another vibration at 0.75-0.775x that caused our Turbine trip several times. The vibration is rise in all probes both turbine and generator, but the highest is in Inboard Turbine. This vibration is ocassionally, sometimes it going up untill 4 microns and sometimes it going down to 0.5 microns. We have also put a velocity transducer to clarify the displacement result, and it seems a true vibration (see attachment). Before deciding to overhaul the Turbine we are now still find another possibilities that would cause such vibration. Please let me know if you have any suggestion or experience. Thanks a lot.

Tanggapan 4 – JONO

Dear Satch,

Did you check about change in 1xVbration? Could you check in your Full Spectrum? Based on your Fig. OTB#1255 on your orbit, the keyphasor dots look like moving, it’s not locked. It means there is symptom of fluid induced instability. Also in your Fig. Time Base Plot 1#8, 2#8, 3#8 and 4#8, the keyphasor dots always moving in 1 cycle. Subsynchronous vibration could be result from rub or fluid-induced instability. You had the gear coupling problem before, and 1x increase up, could you check your lub oil (lubrication) in your gearbox, maybe you will be found shales of metal. If yes, it could be coming from your gear, bearing. 10 years ago, we found it in our turbin gearbox. It’s coming from our bearing.

Tanggapan 5 – Sigit kumoro bekti

Dear Satch,

If I see from your time wave form, It looks like truncated wave form on the positive peak & spectrum, regarding to Charlotte it indicates of :

1. rubbing and you can see it from the orbit, weird one.

2. instability problem, it could be on the lube oil.

3. Misalignment

See Trend, It’s very strange, when trip, the vibration goes down to +- 40 micron pp and remains constant while speed goes down. I never see any vibration like this while speed goes down the vibration will be going down and gone refer to rotor dynamic force except if rubbing occured between rotor and stator. it remains a vibration quiet high.
and from waterfall you can see that 0.77x rpm actually appears while your rotor reach 3000 RPM at TIBV but very small because of small excitation from system.

One more weird measurement, exactly on turbine casing. I think it’s very low. (I will not assume it yet)

I think you better check for:

1. linearity of your displacement probe.

2. Check for alignment (try to meet manufacture requirement due to thermal growth)

3. if any major inspection please check run out to make sure there is no permanent bow at rotor.

Please provide with 100% measurement like spectrum on TOV,TOH, TIV,TIH, as well as ORBIT.

hopefully it helps you

Tanggapan 6 – Ronny Hendra

Hi Satch,

Your plot helps a lot.

I have comment as follows;

1. Your trend plot showed vibration remains constant during transient operation. It was confirmed by your waterfall plot. You tripped approximately at 15:20:28 while your vibration amplitude steady (from your plot at least till 15:24:23). I dear to bet you would have the same result with cascade and bode plot.

2. Therefore, If I were you, I’d stop thinking about open the machine to inspect the alignment, bearing, fluid induced instability, etc as yet.

It is away too much for the time being.

3. I’d check any false signal from probes, proximitors, cabling till monitor, etc to find any instrumentation glitch.

Hope this helps.

Tanggapan 7 – Satch Js

Dear all,

Thanks a lot, i’ll try to discuss all the possibilities with our maintenance guys before we decide to overhaul the turbine, and let you know the result.

Tanggapan 8 – Ilham B Santoso

Hai…Stach,

It seem like I missed this very interesting discussion. Just sharing my opinion among others great concern from our collague in Milis MIGAS, since the vibration appear related with increasing load and the frequencies is at about 0,75X (I believe it should not exact at 0.75X) then it is possible that you may have problem in instabilities due to fluid work. A lot of studies on this issue, may you can find it some in the internet. My gut feeling ( I have not have a chance to look more detail on your plots) you have problem on labyrinth seal clearance that cause instabilities. To confirm this, we can check if there is any symthom of changes on turbine performances such as relation among steam consumption and power generated.

that’s all my only two cents worthed opinion.

Tanggapan 9 – Nis Daniel

Dear Satch

Base on your finding, you may try following checklist.

1 check the bearing (primary suspect) change it if found any defect, defect bearing may lead to overheating the coil, thus stop generator to operate

2 check generator’s foundation (secondary) check for unevenness, and loose bolt/nut

Hope this help

Tanggapan 10 – henky Taro

Hello Satch,

Can you explain which bearings are high vibration value?,

Does harmonic rpm showing on spectrum accompanied by randum frequency?

0.75X rpm is sub syncrone frequency,

This indications are usually caused by Journal bearing wear.

Tanggapan 11 – Ronny Hendra

Hi Satch,

What type of turbine you have ? is it a SOLAR unit ? Is it a direct coupled turbine and generator or it has gearboxes on the middle ? where did you measure the 0.75 x Opr speed vibration ? is it a casing absolute vibration or relative vibration from proximity probes ?

Vibration went high when it is loaded. Seems like thermal growth problem. Have you made some stepwise loading test to the turbine. If you have 12 MW. Load the turbine i.e 2.5 MW and wait till the vibration amplitude stable. Then load i.e 5 MW, wait again. Do that till you reach full load. See if there any change on vibration amplitude and how significant it is during constant load. High vibration change during constant load will confirm the thermal problem. Also see if you have rotor bow with start up and shutdown test. If you can share some bode, cascade, shaft centerline from ADRE, that would be very helpful..

Hope this helps.

Tanggapan 12 – herman rusbar

Hi Satch,

It might be come from the critical speed of the turbine. We also have experience with our 28 MW steam turbine that shut off the turbine suddenly after shaking very bad.
Then we check all the alignment first because we suspect Thermal Growth effect just like Ronny said, and then start again with step by step increasing the load while measuring the vibration and speed.

Hope this helps

Tanggapan 13 – andirahmatyani rahmat

Hi Satch,

It’s need to clarify the bearing type usage before it judged to be caused by bearing.