Prime mover being overheated by motoring generator

[Tedops]

How does a steam turbine become overheated when it is being motored by the generator? Such as in a failure of the 32 device. Furthermore, is the same danger (overheating)involved with motoring a gas turbine?

Thanks, for any help...this is a great forum.

 

[GTstartup]

For the gas turbine situation, there is no concern of overheating. The concern of motoring a gas turbine is "forced cooling" which results in uneven cooling of the GT rotating and stationary parts and can cause rubbing.

I will defer the steamer question to the steam turbine guys here.

 

[GTstartup]

OK I will give it a shot after all. The reason a steam turbine can overheat when motored is due to the lack of steam which is normally required to remove heat caused by windage losses. In fact condensing turbines can even overheat when operated at low loads for the same reason.

 

[ScottyUK]

I normally take a poor view of cross-posting, but if you aren't aware of it there is forum666 'Engine & Turbine Engineering' which is inhabited by some very knowledgable people. You might ask you question there, or point them toward this thread.



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

 

[GTstartup]

I agree with Scotty, However, you will get the same answer

 

[Tedops]

Thanks for the help....much appreciated!!

 

[Luis1947]

The prime cause of distress in a motoring steam turbine is the temperature rise due to the windage losses.
Thus, in the steam turbine, besides the 32 device, there should be a temperature sensing device located in the exhaust hood as auxiliary protection. The device setting is about 250°F to alarm the motoring condition.

 

[Alex68]

When a ST is motored, it is moved by the generator throughout a stopped steam. The long blades of the LP sections are subjected to friction with the steam. This friction produces heat which is not exported by the steam because it is stopped.