Gt generator operating on DROOP mode 1

[npower0073]

Hi guys. As you know we have a GE 9FA gas turbine with a 324 H2 cooled geenerator with Mark VI control program. I want to ask a question about the DROOP mode. According to documentation Gas Turbine works in DROOP mode while synchronized to the grid.

The speed control changes FSR as it needs to change power (watts) in proportion to the difference between turbine speed and the set point. Thus any change in actual speed (grid frequency) will also cause a proportionate change in unit load. This proportionality is adjustable to the desired regulation or “Droop”.

If the grid tends to be overloaded, grid frequency (or speed) will decrease and cause a FSR increase in proportion to the droop setting. If all units have the same droop, all will share a load increase equally. this is a big advantage.

Another advantage of droop control is that the gain of the system is high. If 4% droop is selected, as it is on our unit, only a 1% change in speed will produce a change in fuel flow equivalent to 25% of rated load. This results in fast system response to transient changes and helps hold system frequency.
Normally 4% droop is selected and the speed set point is calibrated such that 104% set point will generate a speed reference which will produce a FSR resulting in base load at design ambient temperature. On gas turbines having a peak temperature control, 104% set point corresponds to peak load.

On Mark VI logic we read the control constant
Load Rate Droop Conversion Constant G1\TNKR1_CONV is set to 4% (0.04 n/d). Is this the constant that speciies the DROOP 4% governor?

For this 4% dropp governor like ours, a change of 1% in grid frequency will modify the gas turbine output per 25%.

Does may analysis make sense and what are the control constants that specify the DROOP characteristics?

 

[byrdj]

Here is one of the turbine tips I found on the PAL webpage. It's explaination of the differances between drop and iso is basically as you stated

http://www.pondlucier.com/TIPS/2002/February 2002.pdf

 

[abeltio]

There are many vintages of the GE droop algorithm.

The most recent one is the so called: constant settable droop.

This means that the droop setting changes as a function of load.

It would be dangerous to give control constants names here without looking at your algorithm.

I've noticed that the mk6 sequence is not as detailed and didactic as mk4 and mk5... maybe you need the "guts" of the mk6 blocks for your specific application.

The 4% droop is a typical setting, it does mean what you said...

The only remark is that it is FSRN, the speed control FSR the one modified by the droop setting.

Once you are in temperature control (FSRT) there is no more frequency response in droop...

Base load will change with speed, but opposite to what the grid needs from the unit: high frequency will result in higher baseload, lower in lower.

saludos.
a.

 

[npower0073]

From what i understand from the logic (although most of blocks concerning FSR, TNH and load are blocked) the 4% DROOP is the difference of TNH from Full speed no lad (TNH=100,3%) to Base load (TNH=104.3%). Is that correct? Also as you said GT governor will be in DROOP mode in all cases except from island mode and base load where it is in Temperature control, at that point FSRT is the lowest of FSR's. I guess that this is done for protection purposes of the exhaust path.

 

[rmw]

Temperature Control is for the protection of the hot gas path components.

rmw

 

[npower0073]

In Mark VI logic there is a task:FSR, with block that selectes the FSR reference each time. This block selects the minimum of FSR. One of those is FSRT which is used for hot gas path compnenents protection, as rmw proposes. But the blocks are not accessible of coyrse (GE typical). SO when the GT runs at temperature control and there is a slight grid frequency increase the turbine speed increases, the compressor discharge pressure increases and so the output increases, is that correct?

 

[rmw]

It has been way too many years since I dealt with GE GT contorol logic, so I won't go there. However, it seems to me that while in Temperature Control in an islanded situation where a load reduction caused the frequency to increase, the GT governor controls would see that and back off the fuel which would tend to lessen the GT output trying to bring the grid back into frequency as best this unit's capability allows.

The problem would be in a load increase scenario while in Temperature Control that lowered the grid's frequency and the GT couldn't respond because the Temperature Control limitation wouldn't let it, so it would slow the GT down with the opposite reaction to what you mention. The controls would see that as over firing for the amount of air available and back the fuel off in either case as I see it.

If the steam turbine has inlet control valves, it could try to pick up or drop load according to it's governor settings, (to the extent that boiler steam is available upon a load increase demand) or if you have duct burner firing, its contribution to the overall situation could help bring the grid back into frequency.

Those more current and smarter than I am can straighten this out if I got it wrong.

rmw

 

[npower0073]

rwm, i am talking about temperature control when you are synchronized to the grid. I have seen this by the curves of GT and it happens exactly that, a load increase to the grid lowers the grid frequency and then the GT output reduces.
Of course this happens when gas fuel control is in TEMPERATURE (FSRT) and not in DROOP.