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6 comments
Active Contributor

Join Date: Apr 2008
Posts: 10

Steam turbine differential expansion

04/02/2008 11:27 AM

total float of the steam turbine we are operationg is 4.5 mm .but the differential expansion limit is -4 mm to +7 mm.This limit is provided by the OEm and set for alarm.

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Power-User

Join Date: Apr 2007
Posts: 418
Good Answers: 19
#1

Re: Steam turbine differential expansion

04/03/2008 2:35 AM

It seems that those are the facts. Is there a question?

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Active Contributor

Join Date: Apr 2008
Posts: 10
#2
In reply to #1

Re: Steam turbine differential expansion

04/08/2008 10:13 AM

We are operating 35 MW turbine.Differential expansion limits given by the manufacturer is -4 to +7 mm.If the total free float of the rotor without thrust bearing installed is 4.5 mm.How is it possible with the safety of the turbine in case o excessive differential expansion.

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Member

Join Date: Mar 2008
Posts: 6
#3

Re: Steam turbine differential expansion

04/20/2008 3:24 PM

I know a little about this, but not sure if i can explain it clearly.

The rotor bump onto the front and rear thrust pads are values you look for when the machine is cold (both the casing and the rotor). I have never seen a value of 4.5mm for this measurement, it seems excessive, but if that is the design value then so be it. The differencial expansion values are for when the machine gets hot (both casing and rotors). The casing and rotor can expand at different rates and in different directions as the machine is subjected to increase/decrease in loads. A drop in steam temperature will shrink the rotor before the casing, on an Impulse rotor the diaphragms and discs will feel this before the rotor. If water carry over is allowed into the turbine the casing will cool faster than the rotor. And so on (this is how I understand it). Also the rotor expansion, with respect to the casings can go in different directions when everything is as it should be. For Tandem machines with 4 or 5 turbines in a row the position of the thrust block must be considered when trying to answer your question. Consider a 500MW + machine, HP-IP-LP1-LP2-LP3. The IP will expand forward, pushing Ped 2 which will push the HP, which will expand forward also, which will push the front standard pedestal forward as well. The LP's expansion will be contained within themselves and will not expand such that one displaced any other. At the same time the shaft is fixed in the thrust and this may be in ped 2. This allows the HP shaft to expand forward of the thrust and the HP casing will go forward as well. The IP shaft will expand backwards from the thrust, but the IP casing will go forward of the Ped 3 (the one in front of the first LP). All 3 LP rotors will expand backwards, but LP1 will displace LP2, which will expand itself as well, and will displace LP3, which will expand itself also. LP3 rotor inside LP3 casing will be far from where it was when cold! All this differential expansion and contraction, when running, has much more to deal with than a simple thrust float when cold.

Hope this helps. Happy to discuss more if you have more questions.

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Anonymous Poster
#4
In reply to #3

Re: Steam turbine differential expansion

10/12/2008 1:48 AM

The above said explanation is correct

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Associate

Join Date: Jun 2011
Posts: 28
#5
In reply to #3

Re: Steam turbine differential expansion

07/27/2011 8:38 AM

first thing that rotor and case expands in different direction because casing hold to one point,it,s allow only one side expansion.in steam turbine rotor move to generator side and casing move to other side.

2nd thing that when steam enter in turbine is direct interaction to rotor and then casing.steam impact almost on rotor.so rotor rapidly expand from casing.

3rd thing that if water carry in turbine it,s collect in lower casing.so its cool casing, not a rotor.if water level increase to rotor then it,s cool rotor.but in condition it,s cool casing rapidly then rotor.

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Power-User

Join Date: May 2011
Location: Chennai, TAMIL NADU, INDIA
Posts: 110
Good Answers: 1
#6

Re: Steam turbine differential expansion

08/30/2011 1:48 PM

Dear Mr. MAHAPRASADRAI,

Your question is not clear. What exactly you want to convey.?

Rajeswari

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