i have been observed physically during ratchet operation that ratchet teeth are engaged and 33 cs limit switch signal goes to logic 1 but the turbine shaft not rotated. anyway, i started the unit in this condition and after firing at speed almost 35%, i observed that clutch disengaged and starting motor has tripped accordingly.

same conditions occurred in the second start but clutch disengaged at different speed.

 

i would like to add something.
our mechanical crew inspected the teeth for clutch side and shaft side, they conclude that both teeth sides are not aligned well. so that the clutch can be easily slip from turbine shaft specially at high speed.

do u agree with this conclusion? is there possibility to clutch to be disengaged during unit running due to teeth slipping?

 

magdy,

Is the problem with ratcheting of the unit while on cooldown, or during starting?

I'm very confused.

I'm not quite clear exactly what you are referring to. There is a jaw clutch with teeth on each half of the clutch used to connected the output of the torque converter to the turbine-generator shaft. The jaw clutch closes the two halves when torque is to be transmitted (which actuates 33CS-1). Torque from the torque converter/starting means engages the teeth and keeps them engaged during acceleration as long as torque is being transmitted from the torque converter/starting means to the turbine-generator shaft.

The design of the teeth of the jaw clutch is such that as the turbine-generator shaft accelerates in speed and the speed of the turbine-generator half of the jaw clutch over-runs (becomes greater than) the speed of the torque converter/starting means side of the jaw clutch the teeth will disengage, the jaw clutch halves will separate. This will de-actuate 33CS-1 and shortly after that the starting means will be shut down.

Your first post was about not being able to ratchet the machine. If the two jaw clutch halves close and at least partially engage but the shaft doesn't rotate even 1/8th of a revolution, then there's something wrong with the ratchet mechanism--not the jaw clutch. The jaw clutch is simply the means for connecting the torque converter (of which the ratchet mechanism is a part) to the turbine-generator shaft.

The second post is seemingly about disengagement of the clutch. Yes; the two halves should be properly aligned, but if the unit is breaking away from zero speed during cranking/starting and accelerating then the jaw clutch is engaging sufficiently to transmit torque to be able to accelerate the turbine-generator shaft. Accelerating the shaft does not require the ratchet mechanism.

However, most machines with ratchet mechanisms employ the ratchet mechanism to assist with overcoming the inertia of the turbine-generator shaft when it's at zero speed ("at rest") during starting. The little "bump" provided by the ratchet during starting is usually required and sufficient to help the starting means break the shaft away from zero speed and then the starting means accelerates the shaft via the torque converter. As soon as the Speedtronic senses shaft speed, the ratchet mechanism is de-energized--but the jaw clutch halves remain engaged as torque is being transmitted while purging and accelerating.

The jaw clutch disengages whenever the speed of the turbine-generator shaft is less than the speed of the torque-converter shaft side of the jaw clutch. So, during normal starting and acceleration of the unit after flame is detected when the turbine-generator shaft speed exceeds the speed of the torque converter/starting means side of the jaw clutch, the clutch halves will disengage. Or, if at any time during cranking, purging, accelerating if the starting means is shut down or the torque being transmitted through the torque converter is not sufficient to keep the jaw clutch halves engaged the jaw clutch will open (dis-engage).

What kind of starting means does the unit have: diesel engine or electric motor or expander turbine or ? If the starting means is a diesel engine, how long has it been since the diesel was serviced/refurbished?

Is there a solenoid which controls transmission of torque via the torque converter (usually device 20TU-1, or something like that)? If so, is the solenoid working properly?

How long has it been since the torque converter--including the ratchet mechanism which is a part of the torque converter (usually)--was serviced/refurbished?

Have you checked/changed the filters in the hydraulic ratchet system recently?

Is the hydraulic ratchet pump (usually a DC motor-operated pump) working properly? How long has it been since the motor was serviced/refurbished? (DC motors have brushes and commutators and they need periodic maintenance.)

Please write back to let us know what you find.

 

really excellent explanation i appreciate your way. let me first answer your question

1- we have electric motor starting means

2- we don't have solenoid to control the transmission.

3- the torque converter was not subjected to refurbish and no maintenance since 2 years. same to the filter of the ratchet system not replaced since 2 years.

now, after i read your excellent explanation i can introduce my question in another way.

normally we observed that the clutch disengaged during unit is running at speed 55% - 60%, then unit continue running to sync speed.
recently we observed that clutch disengaged at low speed 35%, then starting motor tripped and unit also. we try to run the unit second time, same condition happened (at 38%) and we preformed the disengagement of the clutch physically.

the question now, what are the items should i inspected to resolve the problem from instrument point of view and mechanical as well.

your prompt response is highly appreciated.

 

The explanation is already written. Remember? The teeth disengage when the starting means speed is less than the turbine-generator side) and because the turbine is not yet self-sustaining the unit trips on "bog down" ("Starring Device Bogged Down Trip") which should be one of the alarms you are ignoring and have failed to tell us about.

Fix the problem with the starting means and the jaw clutch opening problem will go away. As long as there is torque being transmitted from the starting means to the turbine-generator shaft (meaning the speed of the turbine generator shaft is less than the starting means) the design of the jaw clutch teeth will keep the jaw clutch halves engaged. Hydraulic rams (driven by 20CS-1) close the jaw clutch halves against the springs which are trying to open them. Once the shaft is above zero speed, 20CS-1 is de-energized, and it's the angle of the teeth that keep the jaw clutch halves engaged until the turbine-generator speed is greater than the starting means speed.

At that point the turbine is said to be "self-sustaining", and does not need the torque assist from the starting means. At 35% speed, the turbine is not self-sustaining and still requires the torque assist.

And, whatever other alarms you are ignoring (and not telling us about) should also be investigated and resolved.

If you want any further assistance, you must provide the alarms, in the order of occurrence from the time the operator initiates a START until 20 seconds after the L33CSE transitions from logic "1" to a logic "0".

 

I probably need to be more explicit.

20CS-1 controls the flow of hydraulic fluid to two small, solenoid-operated hydraulic cylinder (small but powerful nonetheless) that are used to close the jaw clutch halves when necessary, and ONLY at zero speed. There are springs (two of them, I believe) that are always trying to open the jaw clutch, so the hydraulic cylinders are necessary to close them. (This should all be visible on the Starting Means Piping Schematic (P&ID).)

If the machine is being started, once the Speedtronic senses the unit is no longer at zero speed 20CS-1 is de-energized, and the hydraulic pressure used to close the jaw clutch halves is "removed." The unit can only be above zero speed when torque is being transmitted from the starting means (starting motor and torque converter) to the turbine-generator shaft through the jaw clutch.

The angle of the teeth of the jaw clutch halves is such that when torque is being transmitted from the starting means/torque converter to the turbine-generator shaft the jaw clutch halves remain engaged (coupled).

The hydraulic cylinders used to close the clutch halves initially are not pressurized during starting and acceleration, so the only thing keeping the springs from separating the jaw clutch halves is the torque being transmitted from the starting means through the torque converter to the turbine generator shaft. (The turbine-generator shaft has a very large inertia and requires a significant amount of torque to accelerate or even to maintain speed during CRANKing (when there's no fuel being admitted to the turbine). And, when the axial compressor rotor is spinning it is moving air, and while it's not producing much pressure at low speed it is still moving a significant amount of air through the turbine and exhaust and that requires torque also.

And the angle of the jaw clutch teeth is such that they will remain closed as long as torque is being transmitted (which means the starting means is trying to accelerate the turbine-generator faster than it can accelerate itself (when fuel is being burned) or to maintain speed during CRANKing when fuel is not being burned).

As soon as something happens to cause either the turbine-generator half of the jaw clutch to spin faster than the starting means/torque converter half of the jaw clutch <b>OR</b> the amount of torque being transmitted from the starting means/torque converter half of the jaw clutch is insufficient to keep the starting means/torque converter half of the jaw clutch spinning at the same speed as the turbine-generator half of the jaw clutch the jaw clutch teeth will separate. And the springs on the jaw clutch mechanism will then open the jaw clutch halves.

The Speedtronic uses 33CS-1 to sense when the jaw clutch is closed, and if it's not closed when it should be closed the Speedtronic will then shut down the starting means (if it's not already stopped for some other reason!). I don't recall if the unit will trip immediately if the speed is below some level, but in any case, if the unit is not self-sustaining (meaning the amount of energy being produced by the hot gases passing through the turbine section is insufficient to maintain turbine speed or accelerate the turbine) and the Speedtronic senses the turbine-generator shaft speed is decreasing for some period of time when it should be increasing, it will annunciate 'Starting Device Bogged Down' and I believe that's usually a trip. (It's not advisable to keep flowing fuel into a machine that is decelerating when it should be accelerating.)

Your description of events is unclear. We don't know when the starting motor is "tripping" (stopping) or for what reason it's stopping and we don't know what alarms are being annunciated. If the protective relay of the starting motor is detecting (rightly or wrongly) some condition that necessitates the starting motor be stopped (tripped) and it does so during acceleration, then the Speedtronic will eventually trip the unit if it's not self-sustaining.

It's as simple as that.

The jaw clutch halves are held together during starting and acceleration by the transmission of torque during starting and acceleration (by the angle of the teeth). The torque is a function of the starting motor and the torque converter. If either of them is not working properly then they can't accelerate the unit to self-sustaining speed. You say the torque converter was replaced a couple of years ago. Devices do fail prematurely, contrary to popular hope.

But, you need to investigate what's causing the transmission of torque from the starting means to the turbine-generator shaft to decrease when it should not be (at approx. 35% speed) and is allowing the jaw clutch halves to separate and eventually resulting in a failure to reach rated speed (and a turbine trip, it sounds like).

It's no more complicated than that.

I have seen some pretty severe damage (tens of thousands of US Dollars--plus lost generation revenue) caused by people trying to force the jaw clutch halves to remain engaged during starting and acceleration when there is insufficient torque being transmitted from the starting means to the turbine generator shaft. So, it's not a good idea to try this; but if you do, please don't have anyone near the clutch to observe the operation; they could be seriously injured, maimed, or even killed.

(By the way, forcing the jaw clutch halves closed during coast down before the unit reaches zero speed is also VERY dangerous and has caused a lot of expensive repairs and resulted in lost generation. Just because something can be forced doesn't mean it should be forced at any time.

 

first of all i would like to thank you about the constant support. then honestly i was not purposely intended to ignore the alarms. i am always kept asking the operation about it. currently, our mechanical section dismantled both sides of clutch because they discovered a decay in both side teeth of clutch which might cause slip (disengage) before the unit reach to the self sustained speed. both clutch sides will subjected for machining to recover the decay for clutch teeth. i will come back soon after the repair completed informing you about the result.
i am so thankful for the positive response.

 

Thank you for the feedback.

We await the outcome of the Mechanical Dept's. work.

One question: Does Operations Dept. use the dot matrix alarm printer, or do they have the ability to print Alarms from files on the GE Mark V HMI? (Many GE Mark V HMIs can store up to 30 days' worth of alarms/events.) A former colleague of mine used to say, "The Alarm printer is your friend!" meaning that a working alarm printer, or the ability to print alarms stored on a hard drive, can be very helpful for troubleshooting.

 

it's nice to keep in touch again.

recently, our mark v HMI Was subjected to upgrade by system HMI software called (ARAIDES). it's very close to cimplicity for mark vi control which using windows. now no more DOS, or file copy. we can retrieve data, report, alarm and events through HMI for for a long period of time.

but we don't have matrix printer.

the alarm history observed during the clutch disengaged at 35% of speed before unit has reach the self sustained speed was (starting means tripped). i believe its due to the change logic of limit switch 33cs from logic 1 to logic zero at 35% of speed.

after i got your excellent explanation,, i believe i can analyze little bit ....

appreciate your constant support, we will meet again after repairing the both clutch sides teeth.

 

magdy,

It would be really helpful if you could be specific about the sequence of events with regard to the premature opening of the clutch during starting.

Is the starting means motor being stopped or tripped before the clutch opens?

Is the clutch opening before the starting motor is being stopped/tripped?

<b>What</b> other alarms are being annunciated just before and for a few seconds after the clutch-opening event?

I was only suggesting using a printout to be able to list for us, chronologically (in order from some time to some later time) the alarms as they occurred. If the alarms which are stored on a hard drive can be printed to any kind of printer (laser, inkjet, etc.) then you could list them each on a separate line with their times (don't need the dates if they all occurred on the same date; don't need Alarm Drop numbers--just times and alarm messages) for us in a reply to this thread. That would be most helpful information.

 

Thanks a lot for this wonderful explanation. only one small remark regarding the starting means dis-engage where you mentioned that Turbine speed will be greater than starting device speed.

As both GT and Starting device are connected together means they have same speed, but the GT TORQUE will be greater than starting means TORQUE which will reject the starting means clutch then 33 CS will detect the dis-engagement, hence the starting means will stop.
Thanks for all these analysis and contributions

 

Yes, and during acceleration increased torque results in increased speed. You are correct in that when the turbine is developing sufficient torque to accelerate the shaft without the torque assist from the starting means the jaw clutch will open. Once the teeth are disengaged because of the speed differential resulting from the torque differential, the jaw clutch opening springs will separate the jaw clutch halves. The speed increase caused by the torque being produced by the turbine will not do much more than open the teeth, at which point the opening springs will separate the two halves.

It sure will be nice to hear from magdy on the results of the repairs to the jaw clutch teeth!

 

Dear Magdy,

Do you have historian at your site?

It'll be very useful to get back any small event change.

OR have you operator saved any images during trip? (normally they used save images if any abnormal noticed).

take care
G.Rajesh

 

> It sure will be nice to hear from magdy on the results of the repairs to the jaw clutch teeth!

dear CSA,

this is magdy again would like to update as i promise u.

With pleasure and appreciation for your constant support. i can declare that instead of repairing the decay of the two sides jaw clutch, we replaced by new (two sides jaw clutch). off course it was not easy to find the spares, but we succeeded to procure it from another plant.

anyway, unit has started smoothly, firm engagement until starting device stopped at self sustained speed, unit loaded and back to commercial service.

at the end
many thanks and appreciation for your support, extending my thanks also to MR. moustapha

 

magdy,

Congratulations, and thanks for the feedback!

 

Dear CSA,

Thanks a lot for this wonderful explanation.
We have an SGT-600 gas turbine with an AC electric motor and SSS clutch as a starter system. We plan to replace the SSS clutch with torque convertor (of which the ratchet mechanism is a part). If we change the starter system, should we remove the SSS clutch? Would you please give me your solutions and comments?

 

I can't offer any advice or opinion on this as I have no experience with SGT-600 turbines.