Frame V Gas turbine trips on High Vibrations


Thread Starter

uday rajhansa

Hi, In our plant one of our frame V gas turbines tripped on High Vibrations. The rpm at which it tripped at first was 3500 and during last trip it has tripped at 4600 rpm against 5120 rpm. Vibrations of first two bearings, i.e. one after accessory gear and the one after turbine rose to trip value. All other parameters including exhaust temperatures, FSR, IGV, Lube oil Temperature, pressure were perfectly normal.

I) What could be the reason of its tripping?

II) How many successive starts and stops are allowed in frame V turbine?

Uday Rajhansa
GE-design Frame 5 heavy duty gas turbines are just about bullet-proof. They are the workhorses of the fleet. They can take a licking and keep on ticking. (And they get quite a bit of abuse in many places around the world.)


Has there been some maintenance done on the unit reecently?

Was it tripped from load while running recently? How many times? What are the most common causes of trips from load? What was the most recent cause of a trip from load while running just prior to this event?

Was it not maintained on cooldown (ratchet or whatever method is used at your site) for the proper length of time when it was shut down?

By proper length of time I mean, if the unit wasn't restarted immediately was it on cooldown continuously before it was re-started?

If it was just restarted after a maintenance outage, was it on cooldown for a few hours at least before it was started?

Essentially, presuming the unit is shut down from load normally (not excessively tripped from load while running) and the unit is on cooldown when it reaches zero speed, and the L.O. header temperature doesn't change during shutdown and start-up, you should be able to start the unit as many times as you can without any problems.

There are many sites with Frame 5s that trip from load many times, and as soon as they get the 'Ready to Start' indication they push the START button and re-start the machine with no problems at all! Some units have synchronizing, self-shifting clutches between the starting means and the turbine shaft and can be re-started before they even reach zero speed.

Are you certain your vibrations pick-ups are working correctly?

But, the big question is still: What has changed?

Vibrations don't just occur on two bearings without some stimulus. And, most GE turbines with Speedtronic turbine control panels have redundant vibration sensors and they also require multiple sensors of a group (turbine, load gear, generator or compressor) to indicate high-high vibrations before tripping the turbine.

But, they don't just "trip" on high-high vibrations for no reason.
You need to look at how this machine has been running in the past. What were vibration levels running at before? Typical vibration limits are at .5 in/sec for alarm, trip is usually at 1in/sec. If this is something that just started was there a hard trip or some violent event that preceded this? If the vibrations are isolated to the turbine I would suspect something related to a blade failure. The frame 5 machines have an issue with a hook/fit failure of the turbine nozzles in the turbine section that I have heard. It sounds like you may need to get some expert assistance, possibly starting with a boroscope inspection. If you have a Bently system you might get some more information from that. But if you are exceeding the trip setpoint of 1 in/sec before you reach sync idle it sounds like something is definately going on, and an internal inspection is probably in your future.

I do not know of any limit to the amount of starts you can do, but vibration problems usually don't fix themselves, and repeated trips are not a good thing. If you can provide more information we may be able to give you some more ideas, but this may not be a fix we can do from here.

uday rajhansa

Dear Sir

GTG I Ratcheting was started on 12.09.2009 at 11.00 hrs for running of GTG for testing of newly commissioned generator protection relay.

GTG was started at 11 am on 13.09.2009 for testing. It got tripped after ignition, before reaching to Full Speed No Load (FSNL) on some false electrical signal.

After this, attempt was made to start GTG but it tripped on High Vibration at around 3550 RPM.

To attain thermal equilibrium GTG was run on fire mode and then it was again attempted start but it again tripped on high Vibrations but at higher RPM. The details of start stops and parameters are given as under:

Lube oil pressure 1.7 kG in all cases, hyd oil pressure > 80 kg, all flow sights having oil. All exhaust temperature their spreads. Wheel space temperature and spreads remained under limit. Bleed valves closed and no abnormality was seen. No abnormal alarm except for high vibrations appeared during running of GTG.

Approximately, 40-45 minutes turbine running on fire mode done between each successive start, to gain thermal equilibrium.

Other Points related to History:

GTG Hot Gas Path Inspection carried out in Feb march 2008 at 1,30,735.5 hours and after that it has completed 7627 running hours till date.

There was no tripping of the turbine since Oct 2008.

GTG was run for 1 hour on 15.07.2009.

GTG 1 was given 24 hours ratcheting from 10.08.2009 at 1000 hrs to 12.08.2009 1230 hrs.

GTG I Last coasting down time before this start was normal. This time is in the range of 14 minutes 40 or 50 secs. After the trippings it has somewhat improved to 15 minute and 10 odd secs.

Uday Rajhansa

Daniel Jacob

We have four Frame 5 GE gas turbines. From my recollection , the times we had high vibration problems were when we had a broken compressor blade and other times when the machine did not ratchet long enough to avoid a rotor bow.

You say exhaust temperature is Ok, so i would rule out compressor bleed valve problems and possible compressor stall/surges.

Is the vibration spiking or climbing gradually?

Is the compressor very dirty, whan last was a compressor clean done?

If you have a vibration diagnostic tool such as Bently Nevada ADRE, you can gather some vibration data from a startup and do an analysis. The analysis will characterise the vibration so as to point to a particular problem.

Do you still have the jaw clutch to engage the diesel starter or have you replaced with a SSS clutch?

Sometimes a tooth on the jaw clutch will break off and cause uneven coupling which results in some vibration.