GE Frame 6b Ratchet Motor

D

Thread Starter

davidmcc

Hi All,

we had a ratchet pump failure failure on our GE Frame 6B gas turbine. it happened when coming off load. We found the ratchet pump motor mountings undone and the supply oil pipe fractured. the motor drive end bearing was disintegrated and entered the motor winding causing burn out. We did not do any ratcheting after the load run. we couldn't use the starting diesel engine to rotate the rotor either because hydraulic ratchet pump is also used to engage the clutch and possibly. also the diesel engine cannot get the turbine turning on it's own, maybe it needs to ratchet to get it started.

Anyway my question is: what should we expect when we try to turn the rotor on ratchet then on crank using the diesel engine. If the rotor is bent and there are high vibes, what is the next step?

Thanks for any advice.
Regards,
David
 
davidmcc,

It's VERY important to keep oil flowing to the bearings when the shaft is hot even if it can't be turned. VERY important. Heat from the shaft can cause the bearing material which is plastic (melting) at about 300 deg F (approx. 150 deg C) and the bearings can be damaged if not cooled by Lube Oil flow when the shaft is hot and not rotating. (That's why the Aux. L.O. Pump runs continuously when the unit is Cooldown (ratchet).)

WAIT 24 hours before trying to turn the rotor with <b>any</b> method.

The rotor, when it's hot, is in the elastic range of the metals used to construct the rotor. That means, it (the axial compressor rotor, that is) will bow under it's own weight--<b>BUT</b> once it starts to cool it will actually return to <i>nearly</i> straight. That takes about 24 hours.

DO NOT open the turbine compartment doors to help with cooling.

DO NOT leave the turbine/access compartment vent fans running to help with cooling.

There is a natural draft drawing air into the inlet and through the compressor, turbine, and exhaust, which will cool the unit.

After AT LEAST 24 hours at zero speed without Cooldown (ratchet) in your case, you can try turning the rotor--either with the ratchet (if you've got it repaired), or with the ratchet/starting motor. (You are right that the ratchet pump discharge pressure is used to engage the jaw clutch halves.)

If you're using the ratchet to turn the shaft, it should only take about 4 hours or so of normal ratchet operation to help restore the shaft to its normal straight condition. If you're using the starting motor to turn the shaft by CRANKing the unit, it should only take about 30 minutes or so to help restore the shaft to its normal straight condition.

If you're cranking, you can then just select FIRE Mode and the unit should fire and hold fuel at warm-up and the heat generated from compression and combustion should help with straightening the rotor the last little bit.

The unit may experience some higher-than-normal vibrations on the way to FSNL (Full Speed-No Load), but it should make FSNL without tripping on high vibration. If not, and it trips on high vibration, then someone needs to be listening for rubs as the unit coasts down to Cooldown and ratchet. And the unit should remain on ratchet for at least four hours before another START attempt is made.

But, this happens a LOT more than most people realize. PATIENCE is the key.

Hope this helps!
 
davidmcc,

One more thing:

Two people should be stationed, one on either side of the axial compressor, when the shaft is being turned for the first time--listening for "rubs" (which sound more like scrapes actually, like someone dragging their fingernails on a chalkboard). The sounds may be very faint, or they may be pretty noticeable.

If there are rubs, and they are really bad, then it's possible the rotor is badly damaged (unlikely, but possible), and continued efforts to turn the rotor may result in broken compressor blades (rotating and stationary).

If the rubs are bad, then someone needs to make a decision to stop turning the rotor, wait a few hours longer and try again, or possibly use a borescope to examine the machine.

Also, please write back to let us know how this turned out for you!
 
>Anyway my question is: what should we expect when we try to
>turn the rotor on ratchet then on crank using the diesel
>engine. If the rotor is bent and there are high vibes, what
>is the next step?

If the rotor has sagged to the point where blade tips come in contact with the shroud, then possibly you will have extensive damage up on crank. At that point also, your seals may be compromised [labyrinth]

If you managed to break the rotor free... on ratchet, I would listen keenly at different points for sounds of contact. If I am satisfied, I would do a slow roll using the diesel,in step increments.

IF the rotor is rolling, crank speed/FSNL and all is good...check your vibration levels then. Good vibs at this point is not an all clear, because there are other critical speeds, but if your ok at this point, with temp our warming of the machine its possible to retain normalcy.

NOTE: Not an expert at this, just my thoughts.
I am looking forward to hear the real experts advice.
 
Hi CSA and Albert,

Thanks for your advice.

The lube oil circulation was reinstated but it may have been off for a couple of hours so we don't know the condition of the bearings yet. The ratchet DC pump had a collapsed bearing, fragments of which went into the windings and caused burn out. It has been rewound, new bearings fitted, new coupling fitted, installed and operational again.

Using the local pushbutton, we can get the ratchet pump to run but the clutch didn't engage and there was no ratchet movement. We checked the supply to the solenoid which feeds hydraulic to the clutch, when button is pressed, we get 125VDC onto the solenoid, it's resistance is 440 Ohms (seems reasonable). There may be air in the system causing not enough pressure to engage the clutch and without the clutch engaged there is no ratcheting. Of course the hydraulic pump may not be producing any pressure as it may have run dry due to the fractured pipe so the seals etc may be broken.

Regards,
David
 
> Can you clarify please, did you say that L.O. circulation
> was off for a couple of hours?

Yes, unfortunately that did happen, it was late at night during the weekend and operations discovered the fractured (probably 3/8") pipe and oil all over the baseplate of the compartment, about 3500 litres was lost from the tank. They feared a fire might occur so they shut off the ac and dc lube oil pumps to allow the fractured line to be fixed. They then stated the ac lube oil pump again. A fitter was called in who lives locally but only after they shut off the pump. Once the pipe was repaired was done the pipe and put the pump on a again, probably it was off for between 1 and 2 hours.

The machine came off load at 4th Nov '16 @ 19:42. I was called at 20:30 to report ratchet not working - at that point the oil was still circulating.

Electrician was called in @ 20:56 to troubleshoot ratchet motor not running found blown fuses. Inspected motor and found oil leak. Fitter called in @ 22:30 to repair pipe.

Lube oil was off from 22:20 4th Nov until 00:35 5th Nov (2 hours off) there was approx 3 hrs oil circ after machine came off load before lube oil was off.

please advice what you think in terms of bearing damage

many thanks

We fitted a pressure gauge to the hydraulic system and changed the filters so to day we are going to run the ac lube oil pump and hydraulic pump and see what pressure we're getting, we think it should be around 50 or 60 bar. If it's well down on that figure we will change the hydraulic pump, a new one is expected to be delivered today.
 
Update - no pressure when running ratchet pump, reversed motor direction and now making 30 bar, clutch engaging and ratchet turning, all looks normal. Will try crank run on diesel starting engine next and see what vibes are like.
 
Hi all,

good news on the generator, ran up on the starting diesel engine and no scraping sounds, vibrations minimal <0.2mm/s. Went from auto to fire, ran for about 10 mins warming through again no significant vibrations. Tripped on excessive fuel flow, may be due to our fuel accumulator bladder not being the right spec (borrowed from another system on site because bladder ruptured). Anyway, went for FSNL and ran up fine, got a 10mw test run and ran for 15 mins, max vibe at 10mw was 3mm/s. Looks like those 3 hrs oil circ and no ratchet after load run was sufficient to save bearings. Good that the oil leak wasn't discovered when ratchet failed or ops would have shut ac and dc lube oil pumps off, not being aware of the consequences. Some good learning points in this incident.

Thanks for your help and advice.

Regards,
David
 
Hi All,

we had a ratchet pump failure failure on our GE Frame 6B gas turbine. it happened when coming off load. We found the ratchet pump motor mountings undone and the supply oil pipe fractured. the motor drive end bearing was disintegrated and entered the motor winding causing burn out. We did not do any ratcheting after the load run. we couldn't use the starting diesel engine to rotate the rotor either because hydraulic ratchet pump is also used to engage the clutch and possibly. also the diesel engine cannot get the turbine turning on it's own, maybe it needs to ratchet to get it started.

Anyway my question is: what should we expect when we try to turn the rotor on ratchet then on crank using the diesel engine. If the rotor is bent and there are high vibes, what is the next step?

Thanks for any advice.
Regards,
David
Hi All
I want to procure a ratchet pump which it's Shimadzu serial NO is :G88-71
and Hitachi MFG NO: K966944
I live in IRAN and I want to know the suppliers that I can buy this pump from their company
 
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