droop setting

TNRL (Turbine Speed Reference-Load-biased) is generally the name of the load-biased droop speed control reference when a GE-design heavy-duty gas turbine is controlled using a Speedtronic turbine control system which is configured for Constant Settable Droop speed control.

To be certain which formula is used on a particular unit, one needs to consult the SpeedTronic Elementary, or the CSP (Control Sequence Program), or the Toolbox sequencing.

markvguy

Thank you, but i have a little question i think u can help me.

Suppose the correct formula is :

FSRN=(TNRL-TNH)*FSKNG+FSRN(existing)

and suppose we are connect to the public utility, if the frequency goes up (means the public utlity is loosing some loads) our generator will start to be downloaded because of the excess power from the public utlity.

Now just taking the above example with the following data:

"Machine is operating at 62.5 MW load at 50 HZ and TNR is 102%"

i expect that TNLR will change at same time when the excess power from the public utlity will be available. Basically it will be more then 100% because i expect DWDROOP feedback less the 100% ( let's say 1.9% and therefore TNLR should be 100.1%).

However at the same time also TNH will increase ( let's say to 100.1%) so it looks to me that FSRN will never be operated ( to close the governor valve) because TLRN and TNH will be equal at same time.
As i said this is because i expect our generator to be downloaded as soon as the the excess power from the public utlity will be available.

Maybe i'm wrong but the alternative solution for the above formula is that TLNR is always 100% and TNH is going above 100%.

Thanx

When utility frequency increases while a unit is operating on Droop Speed Control (including Constant Settable Droop) TNH will increase (since TNH is the ACTUAL turbine shaft speed which is directly proportional to frequency). TNRL isn't changing because frequency changes; TNH does. The change in TNH precipitates the change in load. Load won't change unless fuel changes.

When TNH increases, the error between TNRL and TNH decreases which reduces the amount of fuel, which reduces the power output and causes TNRL to decrease because DWDROOP decreases.

That's what Droop Speed Control is supposed to do--and that's why utilities all over the world require generators paralleled with their grids to have Droop Speed Control. When frequency increases, it's because there is more power being provided to the grid than there is load using the power--so Droop Speed Control lowers the outputs of the units operating at part load on Droop Speed Control and that helps to control grid frequency.

Conversely, when grid frequency decreases it's because there is not enough power being applied to the grid to supply the load using the power--so Droop Speed Control increases the fuel to try to bring frequency back to "normal." It's not clear where the FSRN(existing) came from; it appears to be a way of expressing that the value of FSRN from the previous scan of the CSP is being used.?.?.?

You need to use the values of DWKDG for your unit and build yourself a table of values. DWDROOP will never be negative, unless power flow is negative.

Unfortunately, this author has a new computer and no access to his old one, and MS doesn't provide the MS_lineDraw.ttf font with WinXP.... Can we say we love Microsoft? (Actually, this author has made a lot of money because of the way MS does business; it's not easy money--in fact, it can be pretty frustrating at times. But that's the way the world works, eh?) So, a CSP looks like gooble-de-gook without the proper font.

markvguy

Thank you again for your reply.
Last question just for my understanding (hope you don't mind).

If i'm connected to the grid and frequency change is because my network is producing more power then what is required (loss of loads somehere).

Practically the excess power will be absorbed by all the machines connected to the network like kinetic energy increasing the rotor speed and therefore frequency.
(I suppose that all generators connected to the grid and the grid it's self are in droop with frequency at 50Hz, no ISOCH control)

If the droop acts to close the fuel valve
of each generator (including grid itself)reducing the MW ouput according to the speed the total produced power decrease and then again the speed.

It looks that the balance point cannot be reached
at more the 50Hz.

From my understanding i though that new balance point is at smth more then 50Hz but i'm not able to give an explanation. Could you help me?

Thanx for your prompt reply.
I have just an additional question for my understanding, hope you don't mind.

Suppose i have my plant with four generators and the plant is connected to the grid (let's say that TNH is 100%).

If frequency increase is because the grid (which is suppose to be very big) increase the power generation more then required (i.e.some big load has been disconnected from the grid).

Now the extra power coming from the grid should be absorbed by my gererators and all the other generators connected to the grid like kinetic energy increasing the rotating speed of the rotor and therefore frequency in the network (let's say 101% TNH; moreover all generators in the entire network are in DROOP speed control).

Thus all generators will receive a command to close the fuel valve as per droop characteristic.

Now it was my understanding that the new balance point for all the generators is at 101%.

But if all generators are closing the fuel gas valves the kinetic energy coming from the extra power should decrease and all the generators will produce the required power (P generated= P Load).

If so the frequency should drop again to the previous 100% TNH.

Can you clarify me better how the generators will respond in DROOP and how the kinetic energy is changing with different transient condition?

Thanx

Yes, it would seem that a stable point will not be reached. But, in reality, the dynamics of an electric grid is a science all by itself.

The discussions here have all been under "ideal" conditions and do not necessarily reflect what would happen on a real grid, especially a large, "infinite" grid.

Grids can be "soft" or "hard." Stability depends on lots of factors, including the distances between generators and loads. The types of generator prime movers (combustion turbines, steam turbines, hydro turbines, reciprocating engines, wind turbines, etc.) all respond differently to changes in load/frequency caused by frequency excursion.

It is recommended you refer to some texts on electric utility grid control for the finer details you are searching for.

The real effect of droop speed control is to reduce the effect of frequency excursions, not to completely correct them. Grids require monitoring and control to maintain stability and frequency control.

markvguy

Hi markvguy,

I am new in this forum, I have been working in hydro plant, and I have some question about this topic. Could you give some explanation about how to tune PID controllers? I mean, are there the same gains (PID) for interconected and aislated operation? Do you give some matematical models to demostrate it?

I hope your help.

Atte: Mark

Unfortunately, markvguy has no experience with hydro turbine control systems and tuning of their PID controllers.

Woodward Governor Co. has some manuals on line on their website. Their manuals usually have some very good generic information on PID loop tuning.

markvguy

Thank you for your answer. I searched the web of Woodward Governor Co., and I found information about gas turbine, but hydro turbine.

Regards,
Mark