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turbine inlet temperature determines the highest temprature inside the machine.

1) is it constant through out the machine run i.e startup and load mode.

2) recently some manufacturers have given selection modes for setting this temprature and increased the maintenance inspection intervals. how is it decided which temperature to select.

On many (most) machines the temperature in the combustor where the flame is present is higher, and in many cases much higher, than the turbine inlet temperature. Flame temperature has been measured in some machines at nearly 3000 deg F, and a large portion of the axial compressor discharge pressure is used to cool and dilute the combustion gas temperature before it enters the first stage turbine nozzles because most materials used in turbines today cannot withstand such a high temperature (for very long).

Some manufacturers refer to the turbine inlet temperature as the "firing temperature", though that's not a technically good definition or usage.

1) No; it is not constant through out the machine, nor it is not constant during start-up or loading.

2) Yes; some manufacturers are providing methods to adjust the maximum turbine inlet temperature to lower value(s) than the unit is rated at and because the thermal stresses are reduced at the lower temperatures the parts life is anticipated to be longer. Of course, the power output of the unit will be lower at lower turbine inlet temperatures, but some people don't need all the power and some people have spreadsheets that tell them that being able to produce slightly less power and prolong unit operation before shutting down for a maintenance outage will actually save money and increase profits in the long run.

Dear CSA,

Thanks for replying to my queries. I wanted to suggest in a 5 year operated combined cycle plant which has run with 50 % PLF (due to fuel constraints), that considerable saving can be done in EOH i.e Interval of maintenance can be increased. As the Turbine Inlet temperature can be reduced, has this been done at any plant?

Yes; it's been done.

From the previous reply:

>2) Yes; some manufacturers are
>providing methods to adjust the maximum
>turbine inlet temperature to lower
>value(s) than the unit is rated at and
>because the thermal stresses are
>reduced at the lower temperatures the
>parts life is anticipated to be longer.
>Of course, the power output of the unit
>will be lower at lower turbine inlet
>temperatures, but some people don't
>need all the power and some people have
>spreadsheets that tell them that being
>able to produce slightly less power and
>prolong unit operation before shutting
>down for a maintenance outage will
>actually save money and increase
>profits in the long run. <

One can decrease the maximum turbine inlet temperature to reduce thermal stresses and -cycling, but the power production at "full load"
will be decreased. Decreasing the maximum firing temperature won't do anything for a unit which is run primarly at 50% load or less than "full load" since the turbine inlet temperature will always be less than the maximum at less than full load. We also presume we are talking about heavy duty gas turbines, and not those aircraft derivatives, which operate similarly but differently.

GE has a document, GER-3620, which has a lot of technical details related to operation of their gas turbines which you may find helpful. I don't have a copy of the latest version (which corrects some technical errors and provides some improved timetables); you'll need to contact a GE sales or service office to get a copy.

Lastly, when you bandy TLAs (Three-Letter Acronyms) about, please know that not everyone understands the lingo in use at your plant. We
presume the PLF is "part load factor" and EOH is "emergency or extended overhaul" but those are just guesses. Take a minute and unabbreviate or provide a description of any acronyms or abbreviations you use; even if they're in "common" usage everywhere, there are lots of people who are learning things (and terms) for the first time here, many of whom do not speak English as their native language.

Dear CSA,

Thank you for reminding me that am too a learner on this web site. I will hence forth not use Short forms. By the way EOH - I meant Equivalent Operating Hours, and PLF - Plant Load factor.

If this plant has been operating on 50% plant load factor and therefore does very few base load operations in a year. The turbine inlet temperature is already lesser than base, can there be negotiation between the Original equipment manufacturer and owner to raise or increase the intervals of Maintenance. Has this been done anywhere? Keeping in mind the unit has already undergone one Major overhaul. I am discussing frame machines and not aeroderavative.