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rotation speed

rotation speed

rotation speed

(OP)
We have got gas turbine model GT10B-Alstom and this turbine is double shaft (HP turbine and low pressure turbine)the HP turbine speed is variable and power turbine speed is constant as 77300 and reduucedto 1500 rpm to generator speed
The generator shaft is drived from both side steam turbine side and GT side through SSS clutch, when GT is stopped and ST is runnibg there are small speed 89 rpm at power turbine of GT where SSS clutch disengaged from GT side
Please, from where speed comming and is this problem and if yes how can solve

RE: rotation speed

Does your GT have a turning gear or similar device that rotates it while it is off in order to keep it from bowing?

rmw

RE: rotation speed

GTs are equipped with barring or turning gear devices in order to avoid rotor distortion after gt is shut down. The turning gear engages at a predetermined rotational speed and rotates the shaft at a constant low rpm until the turbine metal temperature falls to a certain temperature at which rotor will not bow. I suppose your GT rotor turning comes from this barring system. It should automatically stop or your control system should give permission to stop turning gear operation after rotor is adequately cooled down.   

RE: rotation speed

(OP)
GT have barring  after 8hr the barring stopped , but this case only comming when the generator is drived from ST side for all time ,may be this rotation from generator shaft but how SSS clutch is disengaged

RE: rotation speed

Since you have ruled out the barring, is there something possibly dragging in the clutch.  If so, I would expect it to heat up somewhat due to the friction.

Also, I assume that your clutch is between the reduction gear and the generator.  I think there is a typographical mistake in your power turbine operating speed please clarify.  Is the 89 rpm you are giving us the rotational speed of the gear shaft at the clutch, or the turbine rotor speed?

What, by the way is the rotational speed of the turbine rotor(s) during barring?

rmw

RE: rotation speed

(OP)
This turbine double shaft there is no mechanical connection between HP and LP turbine , so power turbine speed is reduced via reduction speed then connect via SSS clutch to generator(double end drive 1500rpm) , so the mention speed is power turbine speed (LP turbine) ,when steam turbine is stopping there is no speed only this case when GT is off and ST is on

RE: rotation speed

It should only be a "problem" if you lose oil to the Power turbine bearings or reducing gearbox...there are marine applications where power turbines "free wheel" with the line shaft yet they have a shaft brake if necessary to stop it for maintenance.  Yet, somehow I suspect that your SSS needs tweaking to get full disengagement when there is no drive torque applied from the GT. I would not want the gears and LP turbine always rolling at a cold condition and low speed.

RE: rotation speed

(OP)
Thanks but what you mean
SSS needs tweaking

RE: rotation speed

(OP)
I have not more information for the mention clutch, can you tell me how can I investigate or what the part for fully eisengamment

RE: rotation speed

I still think there is an error in your turbine speed number that you gave in the original post and the post you did in the automotive forum.  I questioned that before.  While I know that is is probably quite a bit higher than the generator's 1500 rpm, 77K seems a bit much.

Is there any excessive noise coming from the clutch?  (like you can hear anything out in the plant)  Still, you can take a hollow tube and hold it near the clutch with the other end by your ear and hear if there are any unusual noises in the clutch.

I am beginning to suspect that the pawl is dragging due to the low centrifugal forces of 1500 rpm, and if so, then you should be able to hear the ratcheting noises if you can get a good "listen" on the clutch.

Then again, you may just have excessive oil or grease in the clutch that is acting like an automotive torque converter when the clutch is declutched.  If this is the case, the oil should heat up after a while, and the clutch will indicate a high temperature.

If something is physically dragging in the clutch, it should have "lunched" itself by now and either galled or worn down sufficiently to have stopped dragging.

So, look for excessive heat or ratcheting noises.

rmw

RE: rotation speed

Can you clarify your ST configuration. You mentioned a GT, an HP turbine and an LP turbine. (When you say HP and LP, I refer to ST.) And I understand that you use process steam in ST.(no HRSG). Right?

RE: rotation speed

I understood his use of HP and LP to refer to the two turbine shafts of his two shaft GT.

rmw

RE: rotation speed

By all accounts of his input to his own thread...he has a generator between a GT and ST.  The GT is a 2 shaft GT which means it, the GT, has an HP section consisting of a compressor and hp turbine on one shaft, the hp turbine of the gt drives the compressor of the hp turbine section the same as a single shaft gt.  The LP section of the GT is driven by the hot gases exiting the HP turbine...this LP turbine is AERODYNAMICALLY coupled to the HP turbine of the GT. This  LP "power" turbine IS the drive turbine to the generator on the GT end of the generator. There is a reducing gear and SSS clutch between the GT LP "power" turbine and the generator.  The SSS clutch is between the reducing gear and the generator.  The SSS clucth is an "Over-Running" clutch design (ages old)... if the generator speed becomes higher than the LP power turbine speed it will disengage the GT-LP power turbine from the generator.  The purpose is so the generator may be driven solely by the steam turbine on the other end...you stop the gas turbine and the SSS clutch sensing a decrease in drive torque from the GT Power Turbine, disengages the reduction gear/power turbine train and leaves the generator at reduced load with the steam turbine only.  SSS and BLH clutches...I cannot remember for sure which one it is....but as I recall one of them or both are oil operated and speed sensitive, and there might be a pick-up tube which requires and adjustment in height.  I believe for sure the BLH is oil operated but I cannot recall exactly the SSS clutch construction.  In any event, no matter what GT rated speed is, when the GT is taken off-line, the SSS clutch should FULLY disengage.  You should be able to cool the GT and go to "barring" operation and eventually standstill.  The entire purpose of SSS and BLH clutch designs is to switch between primary drivers or share load.

RE: rotation speed

I think RMW is correct - aero-derivative turbines have coaxial shafts carrying a high speed turbine which has no direct coupling to the load and a low speed turbine coupled to the load. The LS turbine is driven by the HS turbine. I agree that the speed of the HS turbine sounds high, probably by a factor of ten or so.

----------------------------------

One day my ship will come in.
But with my luck, I'll be at the airport!

RE: rotation speed

"If the speed of the input shaft is reduced relative to the output shaft, the torque on the helical splines will reverse. This causes the sliding component to return to the disengaged position and the clutch will overrun."  See the Link below.

http://www.sssclutch.com/marinepropulsion/index.htm?welcome.htm~mainFrame
 us old navy guys are still doing it:)

It is the BLH that uses oil and a pick-up.  I had a BLH on the Cummins propulsion shaft and a SSS on the Caterpillar propulsion shaft and an LM1500 in the middle.  The BLH gave us headaches and the SSS never.  But it sounds like his internally sliding helical splined coupler is hangin up and cannot fully disengage.

cheers

RE: rotation speed

The pawls should be fully out of action by centrifugal force. The pawls are located in a shielded circumferential channel and if you are not hearing a lot of munchin and crunchin going on and have no high temperatures in the clutch housing you are possibly seeing a hydrodynamic affect of the pawls acting on the sliding component and helical gear free wheeling the power turbine. Try  a brake if you need the power turbine stopped...

RE: rotation speed

(OP)
Okky, there are two SSS clutches for both sides of generators , my gus is this speed result from gnerator rotation that transfer the torq to PT via SSS clutch then to reduction gear by feadback , is this correct

RE: rotation speed

The actual rotation is being transferred via the SSS clutch.

The other SSS clutch is driving the generator when the steam turbine is online.  

The output side of the SSS clutch between the generator and the PT is rotating at generator speed. This is causing the PT to spin.  A hydrodynamic effect inside the Power Turbine SSS clutch is freewheeling your PT most likely.

RE: rotation speed

(OP)
now , the SSS clutch is disengage between gearbox and generator frrom GT so the coubling between SSS clutch and gear box is not rotating with the same generator speed, I think with speed less than PT beacuse gear box in this case will increase(feadback) the speed , is this correct

RE: rotation speed

The rotation of the Output Hub rotation, (the generator shaft) is hydrodynamically rotating the Input Hub via the Sliding Helical Component...this is rotating the gears in the gearbox  and is thus rotating the PT...the affect cannot be mechanically quantified by gear ratio calculations because the coupling in this case is not mechanical... it is hydraulic.  The SSS clutch has oil inside it right, for lubrication of the helical gear component and ratchet teeth, etc...?? It is just and affect of not having a power turbine brake in my opinion.

RE: rotation speed

(OP)
Thanks , but let us first to specify the reason ,now this rotation from SSS clutch due to not fully disengagement and this hydrodynamic rotation also comming due to sliding compents and that is not fully didengament at SSS clutch, please this is correct (I will be with you please)

RE: rotation speed

The clutch IS disengaged.
The oil inside the clutch in the channel area of the pawls is creating a windage type flow circumferentially around the ratchet teeth between the ratchet teeth and the pawls.  It is acting like a Reaction Turbine... the oil is creating low pressure area on the face of ratchet teeth and creating a rotational force which is transmitting through the sliding component to the input shaft.

RE: rotation speed

(OP)
thanks, I think you ar right but what can I do for you please

RE: rotation speed

(OP)
what you means with windage  type flow

RE: rotation speed

Windage is the affect of the rotating components inside creating a wind. On couplings of large turbine generators, many have the heads of the studs and the nuts covered with a "windage cover" to prevent them from creating a turbulent wind inside the coupling area.  When windage exists in this case, it is rotational.
The close tolerance of clearance between the pawls and the ratchet teeth and the oil and both being enclosed axially by walls on both sides, prevents the ability of minimizing the low pressure area being developed...the ratchet rotates due to this low pressure being developed on the teeth engaging faces by this oily windage.  Much like any airfoil...it must move to the area of lower pressure but in this case it rotates. I do not see any problem if you are not experiencing any high temperatures or noises coming from the SSS clutch.  Cheers and keep me posted if conditions change.

RE: rotation speed

(OP)
no, there is no noise and temp is normal but only there is some oile is dropped may be from mechnical seal and this is normal as approved from my desginer

RE: rotation speed

(OP)
but can you give some web site to be more familiar for this phenomenon ,please

RE: rotation speed

visit friendster.com
join for free
ask to join a group named "Grupo Mio"  there we can talk more about your plant and location, etc... I've traveled all over the world since 1975 for a couple of oem's and independently and find that it is a very small world in this business and maybe I've been to your plant or know your unit specifically.  We cannot exchange emails here so that is why I set up Grupo Mio at Friendster.com

Take care and best of luck.

RE: rotation speed

sakram: the link and acrobat pdf file are here... the affect is not mentioned due to obvious reasons but if you look closely at the design of the ratchet teeth and the enclosure you can see that only this can be rotating the inlet side since with this SSS clutch you are either engaged or disengaged...no partial engagement. If there was any mechanical binding or friction type problem you would have a serious oil heating problem ;)

http://www.sssclutch.com/marinepropulsion/index.htm?welcome.htm~mainFrame

RE: rotation speed

sakram:

the friendster.com group "Grupo Mio" is in the "Professional Organizations" Category and country is Puerto Rico.

RE: rotation speed

In a double post Sakram states that the gear ratio of the gear box is 8:1.  This would put the gear output shaft attached to the SSS clutch rotating at 89 X 8 = 712 RPM which means that the shaft is rotating at 1/2 the generator speed.

Even with that much speed the slip has to be enough to generate some heat somewhere.  I am going with the hydrodynamic whip if there is no noise.

Still, at those relative speeds, there may not be enough centrifugal force generated for the pawl to make it fully retract.

rmw

RE: rotation speed

If the pawls (plural) are even "just" contacting the ratchet teeth at 1500 rpm... my guess is they would not be asking us for advice on why the GT LP is spinning but "why is the SSS smokin' and making lots of different noises...quickly please"

RE: rotation speed

(OP)
Okky , the matter is clear but just for confirm , no 1- the ratchet teeth is conected with output shaft , so the ratchet is rotate with 1500rpm,
2-the low pressure inside the clutch comming from unstable flow inside the clutch,
3-be inform that the pressure of oil input 2 bar and output is vacuum pressure

RE: rotation speed

turboco1,

You and I are on the same page regarding this.  Your statement applies to any internal components pawl(s) or other wise, that are causing enough drag to make the gear shaft rotate at 1/2 the speed of the generator shaft.  It would be a heck of a racket and lots of heat/smoke.

But, if it is lubricant drag, that produces heat too, so I would still suspect that the coupling was at an elevated temperature.  The friction that would produce the rotation would also produce heat as it produced the motion.

On the other hand, it doesn't take a lot of torque to rotate even the largest turbine shaft once it is up on an oil film.  Breakaway torque, now that is something else.  So... can this turbine shaft be stopped from rotating by hand or some simple type of rotor brake?  (Like wedging a board or plank against the shaft or coupling)  And... if stopped, does it begin to rotate again once the braking effort is removed and enough time has passed so that the oil film is drained away?  Are the turbine lube oil pumps on all this time that the PT shaft is turning?

rmw

RE: rotation speed

sakram:

1. The Output hub with the Pawls of the clutch is to the Generator shaft...these Pawls should be extended radially outwards away from the ratchet teeth during rotation. The actual RPM necessary to position these Pawls outward is unknown, maybe you know(?)

2. The Ratchet teeth are part of the Sliding component which is mounted on the Input Shaft or the Gear/PT drive train side

3. What exactly is vacuum pressure..."negative" pressure or actual vacuum?? if vacuum how could you have any oil leakage from the housing seals?

4. It is clear that the Pawls must NOT be extended radially outward FOR ENGAGEMENT with the ratchet teeth...so, the RPM of the Output hub (the generator shaft) must be:

a)below a certain value "X" of RPM and
b)Less RPM Than the Input Hub or Gear/PT drive train.

5. So it would appear that to engage the SSS, the Generator cannot be above "X" RPM, otherwise the Pawls cannot engage the ratchet to synchronize and move the sliding component into engagement.

6. Engaging:

a) the generator is at standstill, the PT is at standstill
b) the pawls are radially inward and engaged with the ratchet
c) the GT/PT rolls up in speed and drives the generator together up in speed
d) unit is synchronized and online


7. Disengaging:

a) the generator is unloaded and removed from service
b) the unit is at Full Speed No Load (FSNL)
c) The GT is cooled and taken off line and its speed decreases
d) the decrease in drive torque from the GT/PT and the free rotation of the generator with No Load causes the Generator to Over-run the GT/PT
e) the helical splines of the sliding component rotate causing the sliding component to move out of engagement
f) the sliding component slides all the way over but the Pawls are still extended radially outward at this high RPM
g) the Pawls and Ouput hub are reducing in speed due to the generator rotor decrease in speed
h) at some speed decreasing, the Pawls will contact the backside of the ratchet teeth, upon stopping of the generator, the Pawls will actually fall in to re-engage the ratchet teeth

Starting the steam turbine looking at the PT SSS clutch:

a) the generator just comes to speed and the Pawls are extened radially outwards and the Output hub is not contacting or engaged at all with the ratchet teeth.

b) the GT cannot be engaged at this high speed simply because the Pawls are extended radially outward by centrifugal force; the generator must be taken off-line and reduced in speed to engage the GT/PT

RE: rotation speed

rmw:

Right.  The windage from the lube spray would cause heat and be noticeable.  The unit has oil scavenging. Scavenging will reduce temperature excursions significantly by sucking the hot oil out as fast as or faster than it is sprayed into the housing.  Aeroderivative GT's use oil spraying and scavenging chiefly just to cool the roller bearings but also to allow inverted flight maneuvers.

RE: rotation speed

sakram:

Look at what rmw is saying... you should verify that your oil scavenging temperatures have not increased over time. Simply due to windage you should be seeing a rise if there was no such windage problem before.  How old is your concern about the PT rotating??  Is this a DAY ONE problem? or initially did the PT NOT rotate when operating on the steam turbine?

RE: rotation speed

sakram:

verify that your scavenge and supply lines are correctly mounted...that is not reversed.

RE: rotation speed

(OP)
again, all parameter for tempratutre and pressure and vibration is normal , so no any physical changes
and for the vacuum pressure , it is for the tank of the return line of oil
but the idea for eng, disengage as foloow:
1-engage:SSS clutch of GT or ST will engage from starting if other is disengage beacuse the gen sped is zero
2- if other is running or gen is drived from one of them . the second is not engage until the power turbine speed reached to synch speed to keep 60 Hz at gen
just i need to know the shape od the input shaft is helical spline
2-

RE: rotation speed

(OP)
again, all parameter for tempratutre and pressure and vibration is normal , so no any physical changes
and for the vacuum pressure , it is for the tank of the return line of oil
but the idea for eng, disengage as foloow:
1-engage:SSS clutch of GT or ST will engage from starting if other is disengage beacuse the gen sped is zero
2- if other is running or gen is drived from one of them . the second is not engage until the power turbine speed reached to synch speed to keep 60 Hz at gen
just i need to know the shape od the input shaft is helical spline
2-  iam join with your web site but where is the categroy of prof org ,please

RE: rotation speed

The sliding component has internal helical splines. The teeth of a helical gear are inclined at an angle to the axis of rotation of the gear. Helical gears are smoother running than spur gears and are more suitable for rotation at high velocities. The acrobat file on the SSSclutches website has a cross sectional view showing the sliding component and internal helical splines.

see:
http://www.ul.ie/~nolk/gears.htm#Gear%20types

scroll about 25% down from Top of fully loaded page: Single and Double Helical Gears

I copied the link to Grupo Mio, use after you log in.
http://www.friendster.com/group/tabmain.php?statpos=mygroup&;gid=65632




RE: rotation speed

phewwww, this is a very long thread...
sakram's problem is a well known problem when using SSS clutches and the GT is shutdown.
some GT OEM's (like GE) installed brakes (solenoid actuated) to stop the GT shaft from turning by viscous drag created by the SSS.
The whole shaftline should be fed by the same lube oil system (single shaft combined cycle configuration) in case the there is a loss of L.O. pressure - the low lube oil pressure trip will protect all the units.
 
i have seen this before and there is no problem... except that there is a nuisance to see GT rotation when there should be none.

the only problem is if there is a need to restart the turbine and the unit does not have flying re-start capability... i.e. a start signal needs a zero speed detection in order to be accepted.

aeroderivative units usually use a hydraulic cranking system so flying restart should not be an issue.

SSS is a very helpful crowd... they will surely be able to suply info regarding this issue and offer solutions.
Also, the GT OEM should be able to assist to implement the brake solution.
In industrial type units (wrongly called heavy duty) the inertia of the shaft is enough to keep the shaft at zero speed once the brakes are released. May be in aeroderivative units you will need to apply the brakes permanently... the power turbine turns so smoothly that you can actually turn it by hand (i've done it).

HTH.

saludos.
a.

RE: rotation speed

(OP)
Dear turbo1.,now at engage:Ratch teeth connect with Pawl and in disengag:ratchet teeth is not contact wih pawl

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