Hello Experts;

Good day. We face a different problem right now. When we start the Gas turbine the vibration are well with in limit up to 84% of the Gas producer means (GP speed). Between 84.3 and 87.6 % the vibration goes high for a 10 second near about 0.38 IPS. after 88 % the vibration become well with in limit.

We capture the vibration spectrum on the GP side with horizontal and vertical locations by using velocity transducers.

We see a high high peak found on 2X with the almost same amplitude on both horizontal and vertical.

The positions of measurement is right after the 11 stage axial compressor.

Please guide me what are the possible reasons?

Regards

 

You don't say what model of machine you have. but I would guess that what you are seeing is the shaft going through it's critical speed so, nothing to worry about.

 

I would say that if this is a recent condition for a machine which has been running without any issues for some time, then is there something which might have "triggered" the problem? A recent maintenance outage? A trip from load?

When was the last off-line compressor water wash performed?

Has the turbine control system and/or vibration monitoring system recently been upgraded?

It could simply be that a new control and/or vibration monitoring system is now providing more accurate information (this happens ALL THE TIME when systems are upgraded and new data/values are available) and this has been ongoing for some time. You haven't said if this has prevented you from running the unit, or if you just "ride through" the condition and continue to run the unit.

There's just not enough information to be of use here. It is suggested that you have a knowledgeable vibration individual come to site to inspect and analyze the data if this is something recent with existing vibration monitoring/controls equipment. It could be serious; it could be simple. But, if this is something not related to the instrumentation/control system then a more in-depth analysis by a knowledgeable vibration analyst is prudent.

Please write back with details as you progress with troubleshooting and resolution!

 

Respected Sir;

The turbine model is Centaur 4702 by Solar Inc. The 100 % speed of the turbine is 15000 rpm. The speed where 2 x occur is not a critical speed. The turbine is zero overhauled and test in the Test Cell facility where this vibration found. In my opinion my be some resonance or bend shaft are the possible reason.

Now whats your opinion and guidelines to fix this?

Regards

 

Quite likely to be resonance rather than bend shaft. From what you have described, the machine seems to have developed a "new critical speed". You mentioned overhauling. Was there any mass addition or removal from the turbine/generator rotors?

Also, was there any work on the compressor side --> was it dismantled?

Any blade replacement work --> were all those that were replaced by a new/overhauled set pre-dynamically balanced at the vendor site?

And most importantly, can you give the pre & post generator-turbine alignment readings? If there was dismantling work was on the compressor-turbine marriage coupling, what again are the pre & post dismantling alignment readings. I think you may need to get the pre readings from the OEM, if the gas turbine had come pre-assembled to your site during installation & if this is the first time you are disassembling this coupling.