MAX Droop


Here's a line copied from a Mark V CNST_Q/SRC file for TNKR3:<pre>TNKR3 107.0 % ; SETPOINT HIGH SPEED STOP</pre>

The signal name description should be the same for Mark VI and Mark VIe (and for Mark IV).

This value is the maximum "operating" value for FSRN. FSRN should NEVER get to this value, but because of the way some (far too many, actually) plants operate using Pre-Selected Load Control, FSRN can reach 107%, and it can cause some "problems" when the plant wants to unload (manually or using Pre-Selected Load Control or even an operator-initiated STOP).

TNKR3 is there to prevent FSRN from going above the value of TNKR3 during normal operation <i>when the generator breaker is closed</i>. Again, on a properly operated unit FSRN should NEVER reach 107% (the typical, default value of TNKR3)--but, again, far too many plants incorrectly use Pre-Selected Load Control to get to and remain on CPR- (or CPD-) biased Exhaust Temperature Control, so it's possible that FSRN can drift up to the value of FSKRN3 (which it never should under proper operation).

Another reason TNKR3 is used (as a limit) is to prevent operators from manually increasing unit speed <i>when the generator breaker is open</i> too far, and possibly up to the overspeed trip setpoint.

In my personal opinion, a value of 107% for TNKR3 is way too high; it should be more like 105% or 105.5% (in some very hot environments).

Hope this helps!
thanks for answer.

Yes. i do agree with you, but there is a question. Where is droop be set in logic?
How can i find out what is the droop vale?

thanks for reply

PC Load Letter

Hi no_bug,

I replied to your other post as well and I am pretty sure that your system has standard Linear droop implemented in your system.

There is no magic droop % constant available in the linear implementation.

In droop mode (FSRNV4 implementation)

FSRN(t) = FSKRN1 + (TNR(t)-TNH(t))*FSKRN2

FSKRN1 - FSR at no load
FSKRN2 - change in FSR required to increase load by (100/Droop) %

The values for a given fuel and valve configuration is known to GE; that's how they set it in the first place.

For example, let's say you run the machine to FSNL (100%). This the FSkRN1 value.

Let's say you need a droop of 4% in your machine. Now you keep on loading the machine to full load and adjust the speed such that it's 96%. Let's say the FSR value you have is FSRFL. Now
FSKRN2 = (FSRFL-FSKRN1)/(100-96).

Now you have the two control constants to implement the 4% droop.

GE does the same in their test bed; they have standard values for the control constants for various configurations, frame sizes and fuel types.

This implementation works well if the FSR is a predictable function of the turbine MW output; i.e. fuel quality / calorific value should not change. In addition, your compressor performance should be steady. Eventually with so many permutations and combinations it got out of hand and they implemented non-linear droop / constant settable droop control.

CSA may have a bit more history lesson on the control logic evolution than me. The equation you have at site is still used typically on smaller frame ( 5/6 ) machines with single fuel capability. Wondering what you have at your site.
First of all thanks for reply.

I already knew how to calculate FSKRN2, but with your answer I completely understand what is my answer.

thanks alot.

PS: in other post i asked what is TLC_Comp parameter which add to FSKRN1 in this formula. i would be glad if you answer that too :)

post link :