Dear CSA,
Good day CSA and other great mentors of this group.

We have applied lots of information explained on this forum on this same topic but no result yet.

About four weeks back, our Gas Turbine Frame 6B (ISO - 42MW) with MkVl control was shutdown normally, but failed to ratchet.

The Fault:
When placed on cooldown (ratcheting), the clutch engages but refuses to turn not until VM2 is used.

It was left for about 48hrs for the rotor to cool.

Work done:
Mechanical,
- cleaned the filter and inspect the check valve and were confirmed okay
- checked the pump attached to 88HR, the rubber coupling found to be okay.
- Replaced VM2 with a good one.
- Opened the HM2 to check the free wheel and bearing, everything was found to be okay.

Electrical,
- checked 88HR and found to be working fine.

We (Instrumentation & Control),
- Checked the switching state of 33CS and its signal cable from MarkVI pane to the device, it was found to be okay,
-Replaced both VH14 and 33HR with new one.
- confirmed the contact state of 33HR and its signal cables from Mk VI to the device to be okay.
- Confirmed the Resistance of 20CS and its cables to be okay, its Relay and fuses on TRLY board were also Checked.
- Installed a Pressire gauge on the ratcheting mechanism, between the filter and VH14.

Operation:
The Gas Turbine was placed on Cooldown, its functioned (Ratchet) for about four hours, the developed the initial fault I.e

-After the 3mins Timer
-20Cs and 88HR were energised
-The pressure was about 50 to 60bar
-The jaw clutch engaged and after a few seconds, 33HR actuated and l33hrf became a Logic 1 ( end of forward stroke)
Then the Clutch refused to turn( to ratchet) (20cs and 88hr were still energised) not until the VM2 was adjusted, the the reversed stroke was completed, the clutch disengaged a little and 20cs and 88hr de energised.

We tried the ratcheting severally but the ratcheting was only completed not until VM2 was adjusted.

Attached is our P&ID for Ratcheting mechanism.

Dear CSA, what else can we do?

Thank you in anticipation of your quick response.

 

Dayo,

Without knowing what the pressures were BEFORE the problems started, it's very difficult to say if the pressures are good or not. Unfortunately, it seems some packagers use different pumps and different ratchet mechanisms which use different pressures.

In my opinion, VM2 is a valve that is used to test the ratchet mechanism without actually rotating the turbine-generator shaft. It's also kind of a "safety" in that when it's in one position it prevents the jaw clutch from closing so if the ratchet pump/mechanism operated the shaft wouldn't turn (because the jaw clutch wouldn't close). I would also have to see the programming in the Mark* to know if l33cse had any effect on the ratcheting if the jaw clutch weren't closed.

Most ratchet problems are the result of dirty L.O. which causes problems with VH14, the hydraulic ratchet self-sequencer. If I recall correctly, the hydraulic ratchet pump draws directly from the L.O. reservoir, and not from the bearing header (which would be filtered L.O.), so if there are contaminants in the tank they will be sucked up by the ratchet pump suction and the internal passages in VH14 can be plugged/choked. And, one of the things that happens is the the filter after the hydraulic ratchet pump ruptures which allows dirt and contaminants to get past the filter. (It ruptures because there's no differential pressure indicator or switch on the filter, and it never gets changed during routine maintenance outages. HINT! HINT! (Put a differential pressure gauge across that filter and see that it is regularly checked AND recorded.))

I don't understand how manipulating VM2 can cause the ratchet to retract.... You have replaced the ratchet mechanism (HM2), and unless the internal rack-and-pinion/ratchet of the new one is or was damaged that should not be the problem. Again, putting VM2 in the position that does not allow the jaw clutch to close and then operating the ratchet should result in the starting means side of the jaw clutch rotating as it goes through a forward stroke and then the ratchet would go through a retraction and then start another partial revolution as it goes back into the forward stroke.

If that works, then I would suspect the hydraulic ratchet pump doesn't have enough pressure/flow to turn the shaft. You've replaced everything else but the pump and the pump motor. Have you checked the current drawn by the pump motor? Current is a GREAT indicator of the amount of torque being produced by an electric motor. If the current is significantly lower than motor nameplate the pump isn't doing very much; it might be producing pressure, but maybe not enough flow.?.?.? If the current is near motor nameplate then the pump is probably producing sufficient pressure/flow.

Again, dirty L.O. is NOT good. Not for many things (servo-valves, included!).

Hope this helps!

 

Dear CSA,
I have eagerly been waiting for your response.

Work done Yesterday,

Confirming the status of Ratchet pump( PH3)

- Ratchet pump of the defective Gas Turbine ( GT2) was installed on a working GT1. GT1 was placed on Cooldown, the ratchet mechanism worked well, which confirmed that GT2 pump is okay. We installed that of GT1 on GT2.

Gauges on Ratchet mechanism line of GT2 ( defective GT)
- a gauge was installed around the filter (Picture1), and the pressure when the sequence starts was about 4.5 Mpa and momentarily got to like 6Mpa when the VM2 was adjusted a little without disengaging the jaw clutch and the pressure oscillates between 3 and 5 MPa when retracting.
- a Gauge was also placed on the F- port of the HM2 (Picture2). when the sequence starts, the pressure built up to 4Mpa and when VM2 was adjusted a little without disngaging the jaw clutch , the pressure oscillate between 2 and 4MPa when retracting.

Gauge on Ratchet mechanism line of GT1 ( working GT)
-a Gauge was placed on the F port of the HM2. when the sequence starts, the pressure built up to 4Mpa and the pressure oscillate between 2 and 4MPa when retracting.

Since same output pressure was established at same F-port of the two GT's, we felt that the fault is domicile around the HM2 (Picture3) ,we are not sure but you mentioned it as part of the possible cause from this statement of your,

""""You have replaced the ratchet mechanism (HM2), and unless the internal rack-and-pinion/ratchet of the new one is or was damaged """"
NO SIR "WE HAVE NOT INSTALL A NEW HM2, WE JUST INSPECTED THE OUTER BEARING."

""""""" I would also have to see the programming in the Mark* to know if l33cse had any effect on the ratcheting if the jaw clutch weren't closed""""""""
Yes CSA, if the jaw clutch is not closed, l33cse becoming a Logic 0 will not allow ratcheting (Picture4),

Our Lab department tested Lube Oil sample and confirm it to be okay..

A mechanical personnel believed the fault is an automation problem, he is asking us to check cables, please help clear this, is there still anything left for us to check as Instrumentation and Control personnel?

Attached are the pictures,

Thank you so much Dear CSA, anxiously waiting for your response.

 

Dayo,

The mechanical personnel are ALWAYS going to say the problem is the automation. ALWAYS. Full stop. Period.

It could be a loose connection. Have you checked terminations in EVERY junction box and sub-junction box of the related ratchet I/O?

I'm trying to understand how VM2--which should only EVER be at one end of travel or the other end of travel--can have such an effect on pressure and operation. Maybe the problem is VM2 is leaking.?.?.? (It has zero wires on it...!) Again, it's NEVER supposed to be in any position other than one end of travel or the other. Anywhere in between is the wrong position. It's NOT a throttling valve; it's a porting valve.

I'm sorry; I'm not there. There's something I'm missing and something I don't understand about what is and isn't happening. It could be a faulty solenoid (20CS-1), or, again a loose termination or loose wire crimp. Are you sure 33CS-1 is properly adjusted?

Remember: The application code (sequencing) in the Mark* doesn't change. If the blocks and inputs/outputs to/from the blocks are all the same in both Mark*'s it's NOT the Mark* sequencing. It could be a problem with relay coils/contacts on the TRLY card for solenoids. We don't know what Diagnostic Alarms are annunciated (if any) when these problems are occurring.

Just be methodical and logical. Even if you've checked everything, check it again. Think about how the testing has been done. You say the L.O. was tested? WHERE was the sample taken from--directly from the L.O. tank, or from a line after the L.O. filters?

If everything has been checked and the problem is still occurring, then something was missed or not checked properly.

Best wishes--don't give up. Believe in yourselves. Be thorough. Don't forget a LOT of nuisance problems are caused by bad connections. Try replacing relays on the TRLY cards with unused relays from TRLY cards. Check the Diagnostic Alarms. And, never--NEVER--give up.

 

I sincerely appreciate your quick response.

We will check and re-check all you have mentioned and feedback will be given.

Thank you.

 

Dear CSA,
Sorry for given the feedback this late.

What was done to solve the ratcheting problem was the ratcheting pump which was checked initially.

This time the ratcheting pump was serviced and placed back ( because we could not get a new one as at that time).

Our Gas Turbine is back on the grid and up till now the ratcheting mechanism has been performing excellently.

Thank you.