Which is a better option insulation class F Temp rise B or H/F

[tayyab1020]

Recently we are working on procurement of new Gas Turbine driven generator. One of the vendor has quoted insulation class H and temperature rise B while others have quoted F/B. We are currently using machines with F/B and donot have any prior experience of H/F. Please let me know if there are any benefits of using H/F over F/B.

 

[TheBlacksmith]

The H/F should allow an increase in power density; smaller machine at present rating or larger rating at present size. If you don't need an improvement, there is no advantage.

 

[ScottyUK]

I'm confused by the information you have posted. Does the machine with the class H insulation system have a class B rise or a class F rise? You seem to have stated both.

Generally I would prefer to keep the machine cool through basic design rather than design it run hot and then insulate it to cope with the higher temperature. Getting heat out is always a problem, therefore the class B rise would be my preference. I assume the rating applies to both the rotor and stator?


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[tayyab1020]

Yes the rating applies to both rotor and stator and it is class H with temperature rise B.

 

[ScottyUK]

If the rise is a class B then if all other things were equal I would go with the Class H insulation system because it should last longer. Make sure you ask plenty questions about the class H insulation system including obtaining an experience list of where it has been used sucessfully on the same machine design. You really don't want to be the first to try a new design of machine.


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[electricpete]

Look at it as thermal margin.

The class H with B rise has more thermal margin than the class F with B rise.

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[electricpete]

With that said, the F with B rise already has a boatload of thermal margin and it is not likely you will get failure from simple thermal aging (unless you plan on seriously abusing the machine: overload, dirty environment, high ambient temperautre, cooling obstructions etc). So I wouldn't put a big emphasis on class H/B over class F/B, but certainly with all other things being equal you've gotta give an edge to H/B.

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[tayyab1020]

Now the vendor has given us two options either go fo H/B which is very expensive or H/F.

We are thinking to go for H/F. If it serves our purpose, why pay more.

 

[ScottyUK]

If it serves your purpose, why ask?

I wouldn't sanction an H/F machine. Too little field experience in the long term of this insulation system and temperature rise: manufacturers won't get to use one of my projects as a test bed for their products.


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If we learn from our mistakes I'm getting a great education!