on droop speed control CSP, control constant DWKDG has a value of 0.05%/MW, what is the droop setting of this turbine (is it 4%, 5% or 6%)? the unit is GE frame 5, mk5 gas turbine.
The units for DWKDG are %/MW. If a unit with a rated power output of 20 MW is to have a droop setting of 5%, (5% / 20 MW) = 0.25 %/MW.
Approximately 60% of the Control Constants in any Mark V are NOT used on that application (F-class units are the exception to this rule--especially single-shaft STAG units!). They are what are known as Max Case Control Constants--the memory locations for them are pre-defined in memory and may or may not be used on any given application.
So, just because DWKDG exists in your application does not mean that Constant Settable Droop is used at your location. Is DWKDG used in your application's CSP? (Again, just because it's in CONST_Q.SRC does NOT mean it's used in the CSP.)
Assuming a rated power output of approximately 20 MW for a Frame 5, (20 MW * 0.05 %/MW) would yield a droop setting of 1.0 % .... 0.05 %/MW is a typical value for a unit rated at 80 MW with a 4% droop setting (4 % / 80 MW) = 0.05 %/MW ...
What is the value of TNR when your unit is at rated power output (that is, when it's on CPD-biased exhaust temperature control)? Or, what is the value of TNR when your unit is at 50% of rated power output?
Using the formula, (21 MW * 0.05%/MW) = 1.05% droop. From your 50% load data, this is approximately correct since rated load would occur at approximately 101.05% TNR, 50% load would occur at approximately 100.5025%.
It appears your unit has an incorrect value of DWKDG.... When one encounters something like this, one has to wonder what prompted such a change from a normal, typical droop seting value of 4% or 5% to 1.05%?
OR, was this overlooked in the engineering phase and during commissioning and what else was changed to make the unit behave "normally" because of this possibly erroneous Control Constant?
How long does it take to load your unit from breaker closure to Base Load if you select Base Load when the breaker closes?
If 50% load is equal to 10.5 MW, then 100% load would be equal to 21.0 MW. If your machine was to have a 4% droop characteristic, then DWKDG should be approximately 0.19 %/MW = (4% / 21 MW).
The presumption is that the loading rates have been changed to make the unit load reasonably slowly with the very low value of DWKDG, so if DWKDG were changed to 0.19 %/MW, it would probably load extremely slowly....
So, BEFORE changing _anything_ you should evaluate the loading/unloading rates and consider the affect the DWKDG change will have on other operational characteristics. The recommendation is to have a knowledgeable gas turbine control engineer review all Control Constants, and the Start-up/Commissioning Report should be reviewed to determine why such a change might have been made to the Control Constant DWKDG. Or, contact the OEM and ask them if that is the desired value of DWKDG for that particular unit/installation.
If the unit has been running satisfactorily for some time, then it's not in the best interests of the unit or the power plant (maybe even the grid--depending on where the plant is located) to change the Control Constant right away just because it seems to be incorrect. This requires some investigation and consultation to determine if this was done purposely, or may have been an omission, before making any changes. And, has been suggested, there are other, related Control Constants which may have been altered which need to be reviewed before changing DWKDG.
