GAS TURBINE Frame 5 mark 6, now gas turbine , according to schedule hydraulic ratchet started so alarm coming on every 3 minutes. alarm is follows

....RATCHET TROUBLE...

WE have also started the heater to reduce the viscosity of lube oil or increase the temperature of lube oil because of cold weather. before heater started oil temperature observed 24 c deg. and after heater made ON oil temperature reached to 32 deg c. but the situation is same is that problem something else if so please help me about that matter. i will be appreciated

 

Please read though the post below , i have explained in detail of the ratchet operating mechanism and the problems and the solutions

http://www.control.com/thread/1288454576

read though it and ask for more clarifications if needed.

 

I want to say a couple of things about this thread to anyone reading this thread. First, two very important pieces of information were not provided.

1) When did the problem begin? After a maintenance outage, or a unit trip, or, when?

And this is probably <b>THE MOST IMPORTANT PIECE OF INFORMATION:</b>

2) Has anyone ventured out to the unit to determine if the ratchet mechanism is actually turning the turbine shaft? If so, is the ratcheting of the shaft what has been typically observed in the past, or is it somehow different from what's been observed in the past?

This is important information, which if provided in the original post, would be most helpful in trying to provide some direction for troubleshooting. Without it, we have to ask more questions and wait for answers.

Second, please remember when posting for help with problems here on control.com, or anywhere for that matter, that the more information you can provide about the problem and what you have observed and what troubleshooting you have done and the results of that troubleshooting the more concise the response you receive will be. We are not there at your site and we don't know the exact configuration of all the auxiliaries at your site. Every Frame 5 is not exactly like every other Frame 5; many changes have been made over the years, mostly to the auxiliaries. The turbines themselves are still pretty much the same workhorses they have always been, sucking and squeezing and burning and blowing while producing torque to drive a load (electrical or mechanical). But, the control systems (and the programming of the control systems) and the auxiliaries have evolved over time.

There is usually some kind of clutch between the ratchet mechanism and the turbine shaft (or the input to the Access. Gear that is ultimately connected to the turbine shaft). Has anyone investigated the clutch to see if it's working properly? I've been told that many of the newer units use SSS clutches, which while they can't be easily observed to determine engagement, there is still a switch (limit or proximity) to provide indication of engagement and/or disengagement.

Has anyone looked at the Starting Means Piping Schematic (P&ID) to determine if there is a filter in the hydraulic ratchet oil supply system and if so has the filter been looked at or changed? (Unfortunately, there usually isn't a differential pressure gauge or switch on the filter, so it commonly gets overlooked. Hint, hint for anyone paying attention.)

Has anyone tried to determine if the pressure to the hydraulic ratchet self-sequencer is normal or not? (Unfortunately, there usually isn't a pressure gauge on the discharge of the hydraulic ratchet pump and one doesn't usually get installed until there is a problem and then no one knows what the normal pressure is and so it can't be determined if the pressure is normal or not. Another hint for anyone paying attention.)

Also, is there anyone on site who is able to look at the application code (sequencing, or logic) in the Mark VI using Toolbox to determine exactly what causes this alarm? Because the application code running in the Mark VI, viewed using Toolbox, is the definitive answer about what causes this alarm at your site.

In the past, this particular Process Alarm would not have been annunciated until six minutes after the Speedtronic failed to detect a ratchet operation as indicated by changes of state of the "limit switch" of the self-sequencer. GE and some of it's licensed packagers/suppliers have been making some "improvements" to sequencing in the past few years, and it sounds as if this might be one of those "improvements".

Lastly, 24 deg C is just at the minimum for starting a GE-design heavy duty gas turbine (meaning breaking the shaft away from zero speed and accelerating it up to operating speed). But, for cooldown (hydraulic ratchet) operation, it should be just fine and should not result in any abnormal operation.

There is usually a description for just about every auxiliary system for a GE-design heavy duty gas turbine in the Maintenance/Service manuals provided with the unit. This is an excellent place to start understanding the auxiliaries and how they work; they sometimes even have descriptions of the conditions which cause alarms.

Best of luck with your problem. Please write back to let us know what the problem was and how it was resolved.

 

thanks CSA next time i will be carefully give the all information. and i will adopt the procedure as per your instruction

 

One of our 7EA turbines will not ratchet automatically.

Here's what we have found:

63HR1 and 2 pressure switches are both functioning properly. The solenoid valve dictating which direction the hydraulic fluid show go is functioning also. We are using a Voith torque converter to do the ratcheting on this unit. We can force a signal to L63HR1R which will allow the turbine to ratchet. We are also using a Mark V control system. We have it narrowed down to no pressure being present to 63HR1R which is the pressure switch on the return stroke, because we placed a pressure gauge where the pressure switch would be at and it only went up to 6PSI. On our other unit, the pressure got up to 544PSI and then drops to zero as it ratchets and then jumps back up so the timer can begin again. We also replaced the solenoid that controls which way the hydraulic fluid moves.

Could the piston on the return side be broken, or be allowing the pressure to be bled off somewhere else in the system.

Let me know if you need anymore info. Thanks.

 

Hello,

Should there be any need, ratchet valves can be serviced.
I work for a company who represents Young & Franklin who are the OEM as far as hydraulic self sequencing ratchets are concerned.
You can contact me if you like.

Omar
[email protected]

 

Will, not to pick on you but it is typically better to start a new thread rather than tack onto an old one that refers to a different style turbine. But in this case it still gets seen so no big loss for you.

I have to make some assumptions with the information you have provided, hopefully these assumptions are correct. I assume you have a Frame 7EA gas turbine, running a Voith torque converter, most likely driving an air cooled 7A6 generator. You have an electrically driven aux. lube oil pump and the same for hydraulic oil.

Your torque converter has a three piston ratchet assembly, 2 pistons for the forward stroke and one for return. Pressure switch 63HR-1 senses when the return stroke is complete, 63HR-2 senses when the forward stroke is complete.

Control valve 20HR-1 controls the flow of hydraulic fluid to the ratchet pistons. In its deenergized state fluid should be ported to the return piston, energized it should port fluid to the forward stroke pistons and allow the return cylinder to drain.

I assume your hydraulic pressure is in spec., around 1500psi.

If all this is ok, and you have the condition you describe it certainly sounds like a problem in the torque converter ratchet assembly. I might see if there was some way to truly test that you have flow to the return cylinder. Are you certain that the 20HR-1 valve you installed is good? And working properly? Have you reviewed your P&ID for the ratchet system?

The question always asked is when did this start? Also curious how many hours and how many starts on your machine?

Anyway if you have flow to the return cylinder but can't develop pressure then it sounds like the fluid is passing somewhere in the ratchet that it should not be. Please keep us updated as to what you find.

 

It would certainly appear there is some leak somewhere that is not allowing the pressure to build up to actuate 63HR-1.

I don't have access to the logic or the piping schematics for this type of ratchet, so the questions aren't as focused as I'd like them to be. I do recall that with the self-sequencing type of ratchet mechanism that when the mechanism reaches the end of a stroke (forward or reverse) the pressure goes very high and that is the signal that the stroke has reached the end of travel. I believe the same is true for this type of mechanism, and that's what the two pressure switches do--sense a very high pressure when the mechanism reaches the end of travel. This is the signal to change flow to the other direction (from forward to retraction, or from retraction to forward). So, I'm presuming that 63HR-1 will be actuated when it reaches the end of a retraction stroke initiating a change of flow to a forward stroke, and 63HR-2 will be actuated at the end of a forward stroke initiating a change of flow to the retraction piston.

When you force the logic, does the ratchet go through a full stroke or a partial stroke? In other words, when you force the logic does this enable the ratchet to complete a full forward/retraction stroke sequence? Does the stroke take longer than normal or shorter than normal? (You could use the other unit's strokes as a comparison.)

Because it would certainly seem that if the piston were broken the ratchet mechanism wouldn't operate properly because there wouldn't be sufficient surface area or the leakage would be so large the piston wouldn't be moved. If the leakage, say past rings, were excessive it would seem the stroke would take longer than normal, or possibly not be a full length stroke.

This is not one of the self-sequencing type of ratchet mechanisms, by the way. The sequencing is accomplished via the Speedtronic.

 

I appreciate all the responses so far, and yes starting a new post would have been best. That's what happens with new users.

We ended up replacing the torque converter and that has solved our ratcheting problems. We are waiting to hear from Voith on what the problem was with our old unit. The return stroke piston was not traveling the full length that it should have and it was stopped right at the opening of the 63HR1R pressure switch. We did a bore-scope of the converter and didn't find any broken linkage or anything visibly wrong. Quite possibly a leak or just worn out. This unit is not a base load unit and has been in service for 4-5 years, so it has a lot of starts on it.

Once I hear back from Voith, I will post what the findings were.

 

Will, as CSA likes to say, "Thanks for the feedback".

It is indeed what makes this site so powerful, besides the knowledgeable people. Don't take my suggestion of starting a new thread to hard, we are all "new" at some point, some like me are new again and again.

It will be interesting to hear what Voith finds, they make a good torque converter, but its a device that is difficult to troubleshoot, and its not something you can just throw on to test. Glad it fixed your problem. I look forward to more posts from you in the future.
BTW another good group to be part of is the Frame 7EA users group if you are not already.

 

Finally got the results back from Voith on what the issues were with the torque converter. Here's the findings:

"Unit was found in good external condition with actuator connection bolts found loose. Minor rust noted on both input and output shafts. Pawl in overrunning clutch found damaged causing the turning issues.
The hardened pawls usually wear at the contact surfaces. Typically, clutch pawls become damaged, cracked and or dislodged due to an over-torque event.

The clutch assembly was replaced due to the damage. The #3 and #8 sleeve bearings were also damaged. The factory installed four lobe sleeve bearings have been replaced with cylindrical sleeve bearings which is a design upgrade."

Hopefully this will benefit someone in the future.

 

Will, thanks again for the feedback. Our two units were commissioned in 2005 and run 24/7. We will be doing a major on our first unit this fall and are planning to pull the TQ and install a new unit which we purchased as a spare that will be rotated out at each major. Most likely we won't see the same failure, but we probably have a lot less starts than you do, and a lot less time on ratchet.