It is observed that in stand by gas turbine (Frame 5) ratchet jaw clutch is getting disengaged automatically after 25-30 minutes of stoppage of scheduled ratcheting. NRV checked for passing and no passing observed. both the hydraulic cylinders replaced checked and found no passing. earlier one installed cylinder found passing. oil supply line filter replaced. 33 HR limit switch adjusted. problem is still persisting. Kindly advise.

 

Rishi Kumar Srivastava,

If the Mark VIe is a recent upgrade from an older or different control system, could it be that no one ever knew the jaw clutch halves separated with the older control system, some time after "...stoppage of scheduled ratcheting...."?

There is usually a spring to keep the jaw clutch halves separated (whether the turbine is running or not), and hydraulic pressure (from the ratchet pump) is used to close the jaw clutch halves with angled teeth against the spring pressure that is trying to keep them separated (open). This hydraulic pressure from the ratchet pump is only applied when the ratchet is operating (approximately every three minutes). Between cycles, when the ratchet pump is not running and 20CS-1 is not energized, the angle of the jaw clutch teeth is intended to keep them engaged during normal ratchet operation, which means a cycle approximately every three minutes.

So, if the teeth are opening thirty minutes after ratchet is stopped, I don't understand what the problem is. Because when the turbine is started OR when ratchet is re-started, 20CS-1 will be energized and the ratchet pump will produce pressure and the hydraulic rams will close the jaw clutch halves against the spring pressure that is trying to keep them open. And, again, "sharp" jaw clutch teeth will keep them closed between ratchet cycles.

Is the machine older? What is the condition of the jaw clutch--are the teeth "sharp" or rounded?

Is something or someone turning the generator shaft or turbine shaft after "...stoppage of scheduled ratcheting...." which I interpret as when the operator selects "COOLDOWN OFF" or "COOLDOWN OFF" is automatically selected by the Speedtronic turbine control panel?

Again, if the jaw clutch halves separate after COOLDOWN OFF is selected, it doesn't affect turbine operation in the least. So, I don't really understand the "problem." Please write back to explain why an open jaw clutch is a problem when the turbine is not on Cooldown. Is there some alarm from the Speedtronic when the jaw clutch is open and the unit is not ratcheting (on Cooldown)?

I do know that on some old(er) machines, the jaw clutch did not have angled teeth to keep then engaged when the ratchet pump is not running and 20CS-1 is not energized, so if your machine is old(er) then maybe the clutch halves are opened by spring pressure naturally and it just takes some time for the hydraulic pressure in the rams to decrease enough for the jaw clutch halves to open. Again, if the Mark VIe is relatively new and the operators have more information on a cute, color display they are noticing something they were never aware of before. (This happens <b>A LOT!!!!</b>) But, open jaw clutch halves when the unit is not on Cooldown (ratchet) is not (normally) a problem for turbine operation.

Please write back to clarify conditions.

 

In our Frame-6B clutch will be in engaged position whether the cool down is ON /OFF. It'll be de-engaged after 70% speed.

In Frame-9E after 20TU energized the clutch will be in closed position.

Take care
G.Rajesh

 

G.Rajesh,

A jaw-type clutch, such as is used on many Frame 6B machines, will stay engaged after cooldown when there is no hydraulic closing pressure via 20CS-1 <b>IF</b> the jaw clutch teeth are "sharp" and not rounded off by forced closing when the turbine shaft is still turning (which MANY sites do to avoid having to wait until zero speed to initiate another start after a failed start attempt or trip from load). The angle of the teeth are the only thing that keeps the jaw clutch halves engaged with there is no hydraulic pressure acting against the spring that's trying to open them. If the teeth are excessively rounded, they won't always stay engaged when there is no hydraulic pressure keeping them engaged.

<b>BUT</b> there is no logic/sequencing which <b><i>requires</i></b> the jaw clutch to be closed/engaged when the unit is NOT on Cooldown and IS at zero speed. At least I have never, in almost 30 years, encountered such sequencing. And, mechanical vibration and clutch opening spring tension can actually cause the jaw clutch halves to disengage when on Cooldown and at zero speed--with no alarms or problems to the turbine operation or start-check permissive sequence.

During a start sequence, when START is enabled and the start-check permissives are met 20CS-1 is energized to close the clutch halves--if they are not closed. But, they don't have to be closed prior to a START. If they weren't closed prior to a START and had to be closed prior to a START, how would one close them? Force the Aux. L.O. Pump to run, force the Hydraulic Ratchet pump to run, and force 20CS-1 to close the clutch halves? And force the ratchet to turn to engage the jaw clutch teeth to get a 'READY TO START' permissive? Then unforce everything and initiate a START? That doesn't seem very "automatic"....

Hopefully the original poster will write back to clarify his condition--and it's pretty certain that it's either a <b><i>perception</i></b> that the jaw clutch halves must remain engaged when the unit is not on Cooldown and is at zero speed, OR that the new HMI gives information that was never before known to operators--that the jaw clutch disengages after Cooldown is complete and the unit is at zero speed. And, they question this now, because they didn't know it before the new turbine control system was installed/commissioned.

If your site is different, G.Rajesh, please let us know.

 

CSA

Thank you very much for your informative reply. Actually, In this gas turbine after replacement of control system in 2011, during start of ratcheting for scheduled ratcheting we observed that some times malfunctioning in Mark VIe control system occur causing false alarms on screen. During troubleshooting we found that after ratchet start command is given emergency lube oil pump (as l33cse is false due to disengage of jaw clutch) and axillary oil pumps are taking start simultaneously. and after getting feedback of Aux. LO pump start, Emergency LO pump stops, during start/stop cycle of Emergency LO pump of about 1 sec 125 V DC supply drops to 60-70 Volts causing false alarms on screen. After that no alarm appears. We are not facing any problem during ratcheting. Now we are planning to separate power supply source to control system and DC Electrical motors (Emergency LO pump motor and its cables already checked). With your explanation it is clear that ratchet sequencing is not responsible for for disengage of jaw clutch.

Thank you once again.

 

Rishi Kumar Srivastava

"...we observed that some times malfunctioning in Mark VIe control system occur causing false alarms on screen...."

If you would list all, or even some, of the "false alarms" we might be able to help you.

The entire scenario you describe is VERY COMMON for GE-design heavy duty gas turbines equipped or retrofitted with Mark VIe control systems. The DC Emer. L.O. Pump is sequenced to be sure it operates during a start from zero speed (it didn't always do that before, but it does with newer sequencing/control systems).

However, if the DC battery voltage is dropping 60-70 VDC when the DC Emer. L.O. Pump is cycled then there is a huge problem with the battery and/or the charger. You said a new control system was installed back in 2011; that means the 125 VDC battery could be very old. Old batteries which have high levels of sediment in the bottom of the cases will actually become voltage "sinks" and reverse polarity when a high current is drawn on the battery bank, and this will cause the entire battery voltage to drop momentarily.

How old is the battery on this turbine?

When was the last time a battery run-down test was performed? (Also called a battery capacity test, this test monitors how long the battery will maintain voltage above a certain level while supplying a DC load with the battery charger disabled. It's an excellent indicator of battery condition.)

Batteries can have the proper electrolyte level, proper specific gravity, and still have high levels of sediment in the bottom of the cases which can cause serious problems if the battery is ever required for powering the DC Emer. L.O. Pump in the event of loss of Main and Aux. L.O. Pumps. Or, even to operate protective relays when a high load is present during a forced outage/turbine trip/plant black-out.

If you haven't determined the health of the battery in some time (even just one or two years in some cases), it's an excellent idea to do so. You could be wasting a lot of money separating the DC loads when the battery isn't really capable of supplying a load in the first place.

A properly sized and maintained battery should be good for 20 years or so, presuming it's kept cleaned and not subjected to high temperature and/or high humidity extremes, and is maintained and inspected properly. Sometimes, it may only be necessary to replace a few cells, and not the entire battery.

Also, when the battery charger is working properly, it will supply most of the load on the battery--up to its output capability. If the battery voltage is dropping 60-70 VDC WITH the battery charger powering the battery then I suspect even bigger problems with not only the battery, but perhaps the battery charger, as well. Output filter capacitors of battery chargers have been know to fail, as have transformers when overheated.

Again, when you are describing a problem in a forum like this it's best to provide as much information as possible. You may be experiencing a lot of alarms (which would be displayed on the HMI screen--where else would they be displayed?!?!?) but, please, list some of them, if not all of them. If you had provided the low battery voltage readings in your first post as well as the alarms you have been experiencing we probably could have gotten to a faster recommendation and probable cause.

Help us to help you--we are not there alongside you seeing what you see every day. Every GE-design heavy duty gas turbine is not like every other GE-design heavy duty gas turbine. Even if they have Mark VIes, or burn gas fuel or naphtha. They all have different auxiliaries and field devices and instruments, though they all have the same functionality: they produce torque to drive a load (a generator, or a compressor, etc.).

Separating DC loads and supplying a new DC source without investigating the problem with the old DC source is just asking for trouble at some point--trouble that could make a bad problem worse.

There have been some Mark VIe retrofits/upgrades installed without proper system grounding. People believe that bolting painted metal to painted metal is sufficient for a ground system, and that's just not true. While the Mark VIe is less subject to some DC supply issues than other Speedtronic panels, it's not immune to every DC supply problem. And grounding is very important to ensuring the health of the Mark VIe.

Something is definitely amiss, and it doesn't sound like it's the ratchet pump sequencing--because from your most recent description it sounds like it's doing exactly what it's supposed to do: exercise the DC Emer. L.O. Pump when the turbine or the ratchet sequence started when the turbine is at zero speed. But, that <b>>>SHOULD NOT<<</b> cause problems with the battery voltage that translate into the Mark VIe problems and nuisance alarms on the GE HMI.

 

Rishi Kumar Srivastava

The problem may also be something is not right with the DC Emer. L.O. Pump motor....

How long has it been since the brushes were examined?

Have you tried just running the DC Emer. L.O. Pump manually for a minute or so to see what the effects on the DC Battery and/or the Mark VIe are? (There is usually a TEST button on GE-supplied equipment; other suppliers would have included something similar, it's certain.)

Please write back to let us know how you fare with this issue--a very serious issue.

 

Mr.CSA,

We have verified, in our case clutch is in engaged position though OFF cool down. We agreed with you that after 20CS energized clutch should get engaged.

But when it should get de-engage?, may be after 20CS de-energize by spring return force. If the above true, Is our spring weak?

Take care
G.Rajesh

 

G.Rajesh,

If the jaw clutch halves remain engaged when Cooldown is selected OFF, that just means the jaw clutch teeth are in good condition--because that's all that's keeping them engaged against the opening spring pressure when 20CS-1 is de-energized.

Whether or not they remain engaged when Cooldown is OFF is completely unimportant to proper operation of the turbine.

Early clutches did not have angled teeth, and they were sometimes difficult to both engage and disengage. And, they quite frequently had rounded edges which made engagement and disengagement even more difficult. The design was changed to use angled teeth to make engagement and disengagement easier. But, the angle of the teeth will serve to keep the jaw clutch halves engaged when Cooldown is selected OFF--if the teeth are not excessively rounded, and if there is no vibration which can help the opening springs to disengage the clutch halves.

Again, it is completely immaterial if the jaw clutch halves remain engaged--or if they disengage--when Cooldown is selected OFF. The only thing which keeps them engaged when 20CS-1 is de-energized is "sharp", angled teeth--which it sounds like your jaw clutch teeth are. I find a LOT of sites with very banged-up, rounded teeth--mainly as a result of forcing the START permissive while the unit is still coasting down to zero speed which is really hard on the jaw clutch teeth.

So, your spring is likely not weak--your jaw clutch teeth are more likely just in good condition and are not banged-up/rounded.

Believing your jaw clutch opening spring to be weak because the jaw clutch halves don't disengage when Cooldown is OFF and 20CS-1 is de-energized is just as wrong as believing the jaw clutch halves should remain engaged when Cooldown is OFF and 20CS-1 is de-energized. Neither being open nor being closed when 20CS-1 is de-energized when Cooldown is OFF affects starting or unit operation.

 

Thank you again Mr. CSA, (I hit like)

We agreed with you, the engaged position will not have impact on the operation.

What could be the purpose of the spring? Can we assume it may help to de-engage mechanically when maintenance need comes to remove torque converter or gear box?

Take care & thank you
G.Rajesh

 

G.Rajesh,

The purpose of the spring is to ensure the clutch halves disengage during acceleration when the turbine shaft speed over-runs the starting means speed--and that the clutch halves remain disengaged during normal operation.

 

The primary purpose of the spring is to insure the clutch retracts on start-up after the gas turbine overruns the starting means.

 

Thank you MR. CSA & Mr. Otised for your replies.

Take
care
G.Rajesh

 

Dear CSA
Sir,

while we were checking our maintenance history records for your recommended check points, On 2.1.14 we observed that on scheduled ratcheting ratchet trouble alarm appeared on screen and ratchet motor tripped on over load. On checking found that motor is taking 11Amp current. while full load current rating is 5.5Amp. Working of ratchet motor and pump checked separately and found OK. 20CS checked and found OK. Oil pr. is 85 Kg. Jaw clutch engaging is working OK but Forward/ reverse cycle is not working.

Pl. advise As advised earlier we checked emergency oil pump motor brushes condition and found OK.

 

Dear CSA,

While we were gathering details as suggested by you, on 02.01.14 we observed during scheduled ratcheting ratchet trouble alarm and ratchet motor overload alarms appeared on Mark VIe screen. It was observed that these alarms appeared after one cycle of ratcheting. On restart of ratcheting found that ratchet motor is taking 11 Amp current against full load current rating of 5.5 Amp. On giving ratchet command, Jaw clutch are getting engaged but forward/retract cycle is not working. Ratchet pump pressure is 85 kg/cm2. Please note that earlier sometimes jaw clutch were getting disengaged after 25-30 minutes of scheduled ratcheting but there was no issue with ratcheting sequence. 20CS checked and found OK. 33hrf is not changing its true state.

Kindly advise

 

I'm extremely confused now.

And I fear any comments I make are only going to make the problem worse.

There is no mention of what was done to resolve the ratchet pump motor overload.

If the unit is not ratcheting, it would seem the most likely cause is the hydraulic ratchet self-sequencer mechanism--and the usual problem with them is oil quality.

On most GE-design Frame 5 heavy duty gas turbines 33HR is activated by the self-sequencer mechanism. 33HR should change state when the ratchet reaches the end of the forward stroke. L33HRF (if properly configured!) should go to a logic "1" when the ratchet reaches the end of the forward stroke. 33HR should NOT change state again until the unit reaches the end of the retraction stroke, which means L33HRF should remain a logic "1" all during the retraction stroke, and change back to a logic "0" when the ratchet reaches the end of the retraction stroke. 33HR should remain a logic "0" all during the forward stroke--until the ratchet reaches the end of the forward stroke. So, L33HRF should remain a logic "0" throughout the forward stroke--until the ratchet reaches the end of the forward stroke.

It is entirely conceivable that the ratchet pump motor overload is being caused by the self-sequencer not reversing the direction of hydraulic ratchet pressure, <b>AND</b> that the relief valve on the ratchet pump is not working properly.

It is recommended you get someone knowledgeable in hydraulic ratchet operation to site to witness exactly what is/isn't happening and who can help with resolving the problems.

Best of luck! Please write back to let us know how the problems are resolved.

 

Dear CSA,

Thanks for your valuable suggestions.

We have resolved ratcheting problem faced on 2.1.14 by cleaning the self sequencing unit in house. Now ratcheting is working OK.

Now we are left with the problem of false alarm on Mark VIe screen on start of emergency lube oil pump due to 125 V DC voltage dip. we are working with your suggestions, we will revert back with details.

Thanks

 

Rishi Kumar Srivastava,

Thank YOU for the feedback. "Feedback is the most important contribution!"(c) here at control.com. It's what makes this site so special and useful to so MANY people.

I'm glad to hear you have been successful, and am keen to know how you resolve the voltage dip issue.