Good day,

we have a problem with the hydraulic ratchet for a GE frame V. When the ratchet engages and after the 1st 45 degree rotation, it is observed a gap (like going partially backward). I have attached a video for better explanation.

Thanks in advance

 

It looks like that you are not getting a full forward stroke to activate 33HR and drive the ratchet in reverse. Are you getting enough pressure, check pump filter, check PCV VR5 setting,etc.

 

Thanks for the video; it's very helpful.

In the video, the right half of the jaw clutch is the one that moves (slides back and forth)--so it is the half that is driven by the starting means and the hydraulic ratchet. I don't see the starting means side retracting; what I see is after the starting means half of the jaw clutch stops rotating the turbine-generator shaft keeps rotating the left half of the jaw clutch slightly in the same direction of rotation. Sometimes that can happen, and it can happen even more often when the unit has a load (reduction) gear between the generator and the turbine. The generator has a different inertia than the turbine rotor and once it (the generator) starts turning then it won't always stop at the same instant in time as the turbine rotor. It can be very difficult to determine if it's the turbine rotor that keeps rotating or the generator rotor--but because the load gear is present there is also some available back-lash in the teeth of the load gear that can also contribute to the situation. (Sometimes people hear "clanging" going on in the load gear after a turbine trip or even a normal fired shutdown; that's the difference in the rotating inertias of the turbine and generator and the back-lash of the gear teeth in the load gear--it's normal, but on some machines it can sound really bad (it's much more easily heard if the load compartment vent fan isn't running during the coast-down; usually the load compartment vent fan is so loud it's very difficult to hear the slight clanging/banging which can naturally occur.)

What's not clear from the video or the post is how the ratchet is being operated/enabled. If I recall correctly, when the ratchet is enabled from the turbine control system (and I'm presuming this turbine uses one of the GE Mark* turbine control systems) the hydraulic rams which serve to engage the two halves of the jaw clutch (by moving the right half of the jaw clutch in the video) stays pressurized (20CS-1, if I recall correctly). This attempts to keep the jaw clutch halves as close as possible to each other in the event that what is happening in the video occurs. (The slanted design of the jaw clutch teeth are another attempt at keeping the jaw clutch halves engaged after a ratchet operation occurs, but if what I suspect is happening then it's not going to work very well.)

Are you experiencing any problems with the ratchet operation? Any Process Alarms? And related Diagnostic Alarms?

I, personally, have never seen the starting means half of the jaw clutch rotate in the opposite direction during a retraction stroke. The design of the ratchet mechanisms I have seen prevent that from occurring (it's called a ratchet for a reason).

If the unit is operating correctly on Cooldown with no related alarms (Process Alarms, mostly) then I suggest there is no problem--other than it's natural to think this shouldn't happen (the driven side (turbine-generator shafts) of the jaw clutch should not continue to rotate after the driving side (the starting means side) stops rotating). The fact that in the video the rotation is from top to bottom of the driving side AND the fact that the driving side (the starting means side) does NOT rotate backwards (up) means it's not the ratchet mechanism that's causing the shaft to continue to rotate in the forward (down; anti-clockwise) direction. The driving side of the jaw clutch stops moving and the driven side continues to move after the driving side stops moving.

I believe that in some older units when the turbine- and/or generator shaft bearings get a little worn (increased clearance), and if the L.O. pressure is normal, or even possibly a little higher than it should be, the shafts (turbine and/or generator) can continue to turn after given a "little bump" by the ratchet mechanism. It could also be that the ratchet mechanism is very "strong"--because in my experience, a lot of ratchet mechanisms (driven by DC motor-driven ratchet pumps) kind of struggle to rotate the shaft. The shaft rotates in very small increments during the 45-degree rotation and took more time than the one in the video to turn the shaft 45 degrees. If the ratchet mechanism was very "strong" it would rotate the shaft very quickly (as in the video--quickly being in my personal opinion) and so when the ratchet stopped the shafts may very well keep rotating simply due to their inertia.

Again, if there are no problems with the operation of the ratchet during Cooldown, or even using the JOG pushbutton, and no related Process Alarms, I would say this is unusual, but not unexpected. A LOT of other factors could be contributing to the "extended" rotation of the shafts. Perhaps the ratchet mechanism was recently replaced or refurbished, or the ratchet pump or pump motor was recently replaced. Perhaps the bearings have increases clearances. Perhaps the back-lash in the load gear is slightly excessive. Perhaps the L.O. bearing header pressure is higher than normal, or was just increased back to normal or slightly higher than normal. Perhaps the ratchet pump pressure is high or higher than normal; I believe there is a filter in the ratchet oil system and perhaps it has ruptured recently and so there is now much less resistance to flow than previously. There are a lot of possibilities--and it could even be some combination of more than one that is contributing to what is seen in the video.

Hope this helps! If you have anything to add, such as work recently done on the ratchet mechanism or starting means or ratchet pump/motor or L.O. bearing header pressure, please write back to let us know.

 

Seconding what CSA has said, my memory of the Frame 5 ratchet is that it works much harder than what we are seeing. The turbine shaft seems to be coasting on once the forward stroke stops. It almost looks like it might not be turning the full rotor during this test. (?)
What I have found to be most helpful during ratchet troubleshooting is to have a pressure gauge on the pump discharge. This is assuming you have the old, separate DC pump style of ratchet with its own relief valve. One can see if the relief valve is opening early, if the slide sequencing is happening correctly or if everything is "normal". Just a thought.

 

I agree with waltrobinson's suggestion that the turbine- and/or generator shaft may not be coupled to the Accessory Gear Box output shaft. EITHER the hydraulic ratchet pump output pressure and flow-rate are really high or there isn't much inertia being turned. Or, as was suggested, the L.O. bearing header pressure is much higher than normal and/or the journal bearing internal clearances are not what they should be. Or some combination of the possibilities.

Yes; a pressure gauge is helpful--but usually ONLY if there was one installed BEFORE suspected issues started AND there is good data from the period before the suspected issues started.

I suppose it could be possible that with no inertia (turbine- and/or generator shafts) connected to the Acc. Gear Box output shaft it's possible that the relief valve is relieving but it's still no explaining why the turbine-generator half of the jaw clutch keeps rotating after the starting means half of the jaw clutch stops rotating. I have seen small gaps open before at the end of forward strokes but nothing like what is occurring in the video.

It would be really good if aegq (the original poster) would respond with more information about the issue and what has been found. AND, what the circumstances were during the recording of the video (such as, was the Accessory Coupling installed between the turbine shaft and the output shaft of the Acc. Gear Box, and if the load coupling between the turbine shaft and the load gear was installed, or if the generator rotor was not connected to the Load Gear output.