Why does the machine run with Temp control mode while on base load (GE machine with Mark V control)?

 

Base Load means optimal power output at any ambient or machine condition. This occurs when the unit is on CPD-biased (Compressor Discharge Pressure) exhaust temperature control (which is what Temp Control means). Ambient conditions (temperature, humidity), compressor cleanliness, and hot gas path parts (combustion liners, transition pieces, nozzles, buckets, etc.) can all affect optimal power output.

That's why power output varies and is not a fixed value while operating on Base Load during the day and throughout the year as ambient temperatures and humidity changes. If Base Load was a fixed value, then at times the unit would running at hotter internal temperatures than it should be and at other times it would be operating at internal temperatures cooler than could be tolerated, or, to maximize parts life the fixed value could be set at a value which is artificially lower than could be at other times.

So, exhaust temperature control allows the unit to run at a constant internal "firing" temperature regardless of ambient or machine conditions to produce as much power as can be produced while prolonging parts life expectancy.

Optimal power output means maximum power output at a reasonable parts life expectancy.