Wheelspace in Gas Turbine

D

Thread Starter

Denice Thomas

Does Wheelspace means space between nozzles and buckets?

Can anybody pls tell what does First Forward Inner wheelspace. First Forward Outer Whelspace, First Aft Outer wheelspace... means?

M/c :GE Fr.VI
 
First, there is no such thing as a Frame VI. There is Mark VI, and there is Frame 6. But not even a Frame 6 controlled by a Mark VI is a Frame VI.

Second, you're close. Wheelspace is the area between the turbine "wheels" and the stationary turbine casing. The space is below the turbine buckets and nozzles, around the shaft. The turbine buckets mount on the turbine wheels, and the diaphragms are the stationary "separators" that the wheels fit in between.

So, the turbine wheels are attached to the turbine shaft. The turbine buckets are attached to the wheels. And the turbine shaft and wheels and buckets rotate between nozzles and stationary casing sections. Each turbine stage has a wheel, and there is a wheelspace upstream (forward) of each wheel and downstream (aft) of each wheel.

There is a "knife edge" immediately below the turbine buckets and that knife edge rotates in very close proximity to a knife edge below the nozzles. This rotating/stationary arrangement forms a seal and that seal is supposed to keep the hot combustion gases from traveling down into the wheelspaces and overheating the casing and rotors (the combustion gases are supposed to travel only through the nozzles and buckets for the most efficiency).

There is cooling and sealing air that is piped into the wheelspaces that is also supposed to keep the pressure in the wheelspace slightly higher than that of the combustion gases passing through the buckets and nozzles. So, this air, in addition to keeping the pressure just slightly higher than the combustion gas pressure is also providing some cooling to the wheelspaces.

If hot gases leak into the wheelspaces, that's not good for the turbine wheels or the casing. And if there's too much cooling and sealing air then it's likely going to flow up into the combustion gas path and dilute the combustion gas temperature. It's all a very delicate balancing act.

Third, in the forward first stage wheelspace of older machines, there was an inner set of T/Cs and an outer set of T/Cs (one set was closer to the shaft than the other set).

That's wheelspaces. The next time you see the turbine rotor out of the machine, look closely at it. The wheels are the part of the shaft the turbine buckets are mounted on. And the idea is to keep all of the combustion gases flowing through the nozzles and buckets and not leaking down into the casing and around the wheels. Also look for the rotating "seals", they are sometimes called 'angel wings' (because they can be damaged very easily when setting the rotor into the shell/casing or when removing it from the shell casing) in addition to 'knife edges' (one side of the seal is usually tapered almost to a knife edge).

Hope this helps. It's very difficult to do without pictures or graphics.
 
but one question, why the second wheelspace AFT and FRWD temperature less than first and third stage

TTWS1FO1 279
TTWS1FO2 276
TTWS1AO1 235
TTWS1AO2 237
TTWS2FO1 231
TTWS2FO2 229
TTWS2AO1 205
TTWS2AO2 206


 
Dear CSA can you give some point to make temp increase in wheelspace temp?
 
I don't understand the question.

Presuming the cooling and sealing air flows are all correct (proper orifices installed in proper places) and the seals below the buckets and nozzles are in good repair and the turbine shaft is operating in the proper axial position, the wheelspace temperatures should be stable and neither increase or decrease over time at comparable operating conditions.

An increase in temperature could mean either the cooling and sealing air flows are incorrect, or the seal strips below the buckets and nozzles are deteriorating or leaking, or the turbine shaft has shifted position axially and the seal strips are leaking.

Other than this, I don't understand the question.

Oops, one more typical cause for wheelspace temperatures to change: Improperly or poorly installed wheelsapce temperature T/Cs after a maintenance outage.

Wheelspace temperatures are values to be monitored over time for trends, either increasing or decreasing. If they increase very quickly, then there's probably other indications of problems, like vibration or exhaust temperature spreads, for example. If they increase or decrease over time and never stabilize, then that's an indication of problems such as above.

The value of a wheelspace temperature at any given instant in time is pretty meaningless. It's the relationship of that value to the one the previous hour, or previous day, or previous week, to determine if the value is increasing or decreasing over time and by what rate.

This topic has been covered in previous threads on control.com. Use the 'Search' feature to find more information.
 
Maint,

<p>TTWS1FOn - Turbine Temperature, Wheelspace - First Stage Forward, Outer T/C #n
TTWS1A0n - Turbine Temperature, Wheelspace - First Stage Aft, Outer T/C #n
TTWS2FOn - Turbine Temperature, Wheelspace - Second Stage Forward, Outer T/C #n
TTWS2AOn - Turbine Temperature, Wheelspace - Second Stage Aft, Outer T/C #n</p>
I don't see a "third stage" wheelspace temperature in the list (it would be TTWS3.... )

The temperatures are generally decreasing from 1st stage forward to 1st stage aft to 2nd stage forward to 2nd stage aft. I wouldn't consider a 4 deg difference to be an increase of any magnitude. I would attribute that to improperly installed T/Cs (either 1st stage aft or 2nd stage forward; can't be sure, could even be both).

Wheelspace temp's should decrease slightly from one stage to another, presuming everything is working correctly. The difference in your example from 1st stage aft to 2nd stage forward is negligible.

Again, as has been said many times before on control.com: The value of any reading at any instant in time is virtually meaningless. The difference in readings over time (the "trend") is the most important value. Is the value increasing or decreasing, and how fast is it increasing or decreasing? If the values you are reporting are stable and aren't increasing or decreasing with time, then they're likely just fine, and any small anomaly like the one you are seeing is attributable to installation.

The next time the turbine is apart and the transition pieces and the turbine rotor is removed from the casing, get in and follow the wheelspace guide tubing from the outside of the casing to the diaphragm and the "nipple" that the T/C has to be routed into. When the unit is assembled and one of the last things that's done is to insert the wheelspace T/Cs into the unit, it's very difficult to get them properly installed. Because one cannot physically see the tip in the "nipple" to see if it's even in the nipple, is touching the nipple, or if it's touching the metal around the nipple. It's just very difficult to "snake" (route) the T/C through the guide tube and into the nipple. Sometimes the T/Cs come with the compression ferrules "set" (compressed) in the proper place to make installation a little easier (presuming they were purchased from GE; lots of people buy their components from other vendors who don't set the ferrules to make installation a little easier).

The readings you have provided are actually very "good" in that there are not high differentials between the #1 and #2 T/Cs in the same wheelspace. When the T/Cs are very poorly installed, the readings can have very high differentials, which is physically impossible unless there is a catastrophic failure which would likely render the turbine inoperable. (If the T/Cs are properly installed, or even similarly poorly installed, they will read very similarly, because the turbine wheels are rotating at very high speeds (3000 RPM or 3600 RPM or approx. 5100 RPM) so the "air" in the wheelspace, which is relatively thin and small) is rotating very fast and mixed very well! So, large differentials between T/Cs installed in the same wheelspace are likely the result of poor or improper installation.)

So, again the readings in your example are pretty good, and even with the very slight "increase" from 1st stage aft to 2nd stage forward, which again is negligible. The important thing is what are the readings doing over time. Are they increasing or decreasing or relatively stable over time? How quickly are they increasing or decreasing if they're not stable?

Does this answer the question?
 
Basic reasons for improvement of Wheel space temperature:

1. Restriction in cooling air lines

2. Excessive distortion of the shaft

3. excessive distortion of the Exhaust diffuser

4. Thermo couple malfunction

5. wear of turbine Shrouds/Seals

6. Malfunctioning of combustion system

7. Leaks in the cooling air lines

8. Ambient conditions: High compressor inlet temperature leads to increase the compressor discharge (extraction’s to supply the air for Rotor cooling) temperature. But some machines, compressor discharge/Extractions cooled externally before supply the Cooling air for cooling—For this type of systems, compressor discharge temperature is not a factor for rotor cooling.

9. Condition of Air intake system- dust absorption capacity--- dust will leads to choke the cooling air lines over a period of time.

10. After Cooling, Cooling air pressure (which is entering in to the Hot gas path) should be greater than the hot gas pressure in the turbine at any particular location--- Normally it will happen for external cooling machines(This is depends on the pressure drop across the heat exchanger and pipe lines).

11. Improper positioning of thermo couple.

I hope it is useful for you.
 
Hi to all,

one small correction I am posting which is belongs to point no-10.

Before correction: After Cooling, Cooling air pressure (which is entering in to the Hot gas path) should be greater than the hot gas pressure in the turbine at any particular location--- Normally it will happen for external cooling machines(This is depends on the pressure drop across the heat exchanger and pipe lines).

corrected statement: After Cooling, Cooling air pressure (which is entering in to the Hot gas path) should be greater than the hot gas pressure in the turbine at any particular location--- Normally it will "NOT" happen for any machine except external cooling machines(This is depends on the pressure drop across the heat exchanger and pipe lines).
 
B

bharadwaj veturi

TTWS1FI1 174
TTWS1FI2 189
TTWS1AI1 219
TTWS1AI2 208
TTWS2FI1 297
TTWS2FI2 257
TTWS2AI1 277
TTWS2AI2 277

Are the above readings fine, and what does "O" stands for in the previous post tags where as in my case it is "I" on Mark-VI Based GE Turbine.

TTWS1FO1 279
TTWS1FO2 276
TTWS1AO1 235
TTWS1AO2 237
TTWS2FO1 231
TTWS2FO2 229
TTWS2AO1 205
TTWS2AO2 206
 
As explained above in this thread, "O" stands for 'Outer', and "I" stands for 'Inner.'

No one can say for certain if any wheelspace temperatures at any given instant in time are good or bad. There are simply too many intangibles (how long has the unit been running (since it was last started)?; what load is the unit at?; how long since the wheelspace thermocouples were replaced?; but most importantly, have the individual temperatures been increasing or decreasing with time and by how much have they been increasing or decreasing with time (rate of increase/decrease)).

Short of a catastrophic failure which would likely have resulted in a trip and/or damage to the turbine section of the machine, it's physically impossible for the temperature on one side of a wheelspace to be be different than the temperature on the other side of the wheelspace.

The wheelspace temperature T/Cs are intended to measure the air temperature in the very small axial distance (mm) between the stationary portion of the turbine casing and the rotating turbine wheel(s). The rotating turbine wheel is spinning at anywhere from 3000 RPM to as much as 5100 RPM--mixing the air in the wheelspace. That's anywhere from 10 rev's per second to 85 rev's per second. It's simply not possible for the air temperature in any wheelspace at any point in the wheelspace to be different from any other point in the wheelspace because it's continually being mixed by the rotating turbine wheel!

Having said that, the way the wheelspace temperature thermocouples are inserted into the "thermowell" has a <b>GREAT</b> effect on the measured temperature. The thermocouples have to be pushed through stainless steel tubes up into the thermowell (sometimes over distances up to a meter in length), and if they are not positioned properly in the thermowell they will not accurately measure the temperature in the wheelspace.

And, since there are two thermocouples in each wheelspace there is twice the opportunity to improperly insert the wheelspace temperature thermocouples in any given wheelspace. Which means the differential in any given wheelspace can be high--but that's <b>NOT</b> because the actual air temperature in the wheelspace is different on the two sides of the machine; it can't be! It's because of the improper insertion of the thermocouple(s) measuring the wheelspace air temperature.

Most wheelspace temperature thermocouples are inserted after the machine is put back together, and it's not possible to see how the thermocouple tip is positioned in the thermowell (it's not even possible to see when the machine is open!).

So, the only indication that can be trusted with regard to wheelspace temperatures is the trend of the wheelspace temperature readings at similar turbine loads. Even if there is a high differential between two wheelspace thermocouple readings, if a problem with the cooling in a wheelspace develops causing the air temperature in the wheelspace to increase (or decrease) <b>BOTH</b> wheelspace temperature readings in the wheelspace will increase (or decrease) at the same time. (Remember--that turbine wheel is spinning and mixing that air all the time!) If the rate of increase (or decrease) is fast, then it's pretty likely something is definitely amiss. If the rate of increase (or decrease) is slow, then it bears monitoring over time. If the rate of increase (or decrease) is sudden and large, then something is probably definitely wrong.

If the wheelspace temperature differentials or magnitudes are suddenly different immediately after a maintenance outage during which the wheelspace thermocouples were removed and re-inserted, then it's probably a problem with the way the thermocouples were re-inserted, and should be monitored over time. If the temperature magnitudes/differentials are really high, then the suspect T/Cs should be removed, inspected, and re-inserted and/or replaced, as necessary and the temperature checked again after the turbine is re-started.

But to simply present a set of wheelspace temperatures without any indication of running conditions, history, load, etc., and ask, "Are these okay?" is, well--it's just impossible to make any comment with any degree of certainty that is meaningful.

It's extremely unfortunate that GE or their packagers have never really explained what wheelspaces are, how the temperatures are measured, and what kind of problems can occur with the temperature measurement(s), and what kinds of real wheelspace temperature problems can and do occur. But, it's a fact--they don't, and they haven't, and they won't likely ever do so.

The next time your machine is open during a maintenance outage (the turbine section is exposed and you can look down between the turbine wheel and the turbine casing ("diaphragm"), make sure to examine it closely. Also, if the rotor is remove, be sure to look at the turbine nozzle segments where the wheelspace thermowell is located; it looks like a "nipple" (a small bump).

Also, follow the tubing from the place on the outside of the turbine or compressor discharge casing to the nozzle segment to see just how long it is and how many bends are in the tubing. At the very end of the tubing the tip of the thermocouple has to make an almost 90 degree bend! And all of this is done without being able to see the tip at all.

I know this is difficult to imagine; but the next time the turbine is open, make it a point to go out and check out the wheelspace, and the wheelspace temperature thermowells, and the guide tubes. You'll never wonder again how two thermocouples in the same wheelspace can read so differently, and you'll understand why the only wheelspace temperature "reading" that matters is the trend of temperatures in a particular wheelspace.

Hope this helps!
 
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