can any body advice me, how to check DROOP and ISOCH function in GE gas turbine Frame 5 and how to adjust it? how to adjust DROOP percentage.
can this lead to trip of gas turbine on reverse power?

 

Let's say your turbine is rated at 20 MW at Base Load and the unit does not have Peak Load capability. This means that at ISO conditions (usually 59 deg F, 60% relative humidity, at its design altitude and atmospheric pressure, and at rated exhaust back pressure), in a new and clean condition (clean compressor and IGVs, new inlet air filters, internal clearances of axial compressor and hot gas path components within specification), and when operating with fuel at design conditions the output would be 20 MW. (How often is a turbine operated under these conditions? Practically never.)

Let's say the unit was configured to have 4% Droop. When it is operating in Droop Speed Control mode in parallel with other prime movers and their generators on a reasonably well-regulated grid (grid frequency is stable and at or very near rated), as the turbine speed reference is increased from 100% (FSNL) to 101%, the load will increase to 25% of rated, or 5 MW.

This is how the unit is "loaded", or, how it's power output is increased and decreased: By changing the turbine speed reference when it's being operated in Droop Speed Control mode.

As the load is increased further (again by increasing the turbine speed reference) to 50% of rated, or 10 MW, the turbine speed reference will increase to 102%.

As the turbine speed reference is increased to 103%, the load will increase to 75% of rated.

And as the turbine speed reference is increased to 104% the load will increase to 25 MW, or 100% of rated.

It's that simple.

Now, when Base Load is selected, the Speedtronic automatically increases turbine speed reference at a pre-programmed ramp rate, and if the machine is being operated at ISO conditions, and is in a new and clean condition, and the fuel is as per design, when the turbine speed reference is approximately 104% the fuel control will switch from Speed Control to Temperature Control.

If the inlet filters are dirty, and the IGVs and compressor are dirty, and the hot gas path parts (turbine nozzles and buckets, primarily) are aged and have some cracking and distortion, and the exhaust back pressure is higher than normal, and the ambient temperature is 40 deg C and the relative humidity is 91%, the turbine speed reference at Base Load will be something LESS THAN 104%, more like 103.45%, or 103.59%--the exact value depends on a LOT of factors, including the BTU content of the fuel being burned, also.

Does the fact the turbine speed reference is less than 104% at Base Load mean the unit does not have 4% Droop? No, NO, and HELL <b>NO!</b> It only means the machine conditions and the ambient conditions are not at rated.

So, how do you determine if the Droop Regulation setpoint is 4%? As you are loading the machine, monitor the turbine speed reference. When it's at <b>approximately</b> 101.0%, for example, make note of the power output of the machine. Let's say it's 4.45 MW. Now, increase the turbine speed reference to <b>approximately</b> 102.0%, and record the power output. If it's approximately 9.45 MW, then the Droop Regulation is approximately 4%--because the load increased by approximately 25% of rated for an approximate 1% increase in turbine speed reference.

Droop Speed Control is about how much the load changes for each percent change in turbine speed reference. Even for a machine that is not being operated at design conditions with new internals within specifications and with fuel that is not as originally thought, the percent change in load for a given percent change in turbine speed reference will be approximately equal to the droop regulation percentage. Exactly? Never. Close? Yes.

It's that simple.

Now, how to test the Isoch function? What is the purpose of Isochronous speed control? It's to control the frequency to be at or near rated. As long as the load on the Isoch machine is more than zero MW and less than Base Load (for the given machine and ambient conditions), if the frequency is at or very near rated, then Isoch Speed Control is working properly. If some load is added (not to exceed Base Load for operating conditions) or subtracted (not to be less than zero MW for operating conditions) and the frequency remains at or very near rated, then Isoch Speed Control is working properly (any other unit which is operating in parallel with the Isoch machine should NOT be changing it's power output as load on the island is increased or decreased--not automatically or manually!).

The turbine speed reference for Isoch Speed Control is 100.00%, with a small deadband. <b>IF AN OPERATOR TRIES TO INCREASE OR DECREASE THE POWER OUTPUT OF THE ISOCHRONOUS MACHINE BY INCREASING OR DECREASING THE TURBINE SPEED REFERENCE, THE OPERATOR IS REALLY ONLY INCREASING THE TURBINE SPEED REFERENCE--WHICH WILL INCREASE OR DECREASE THE FREQUENCY OF THE ISLAND.</b>

So, the "test" of Isochronous Speed Control is that it will control the frequency of the load it is supplying to be at or very near rated (as long as the turbine speed reference is 100.00% and has not been manually or automatically changed).

Yes.

It's that simple.

Now, Droop Speed Control is more than the above. It's really about the difference between the actual speed (which is a function of the grid frequency) and the turbine speed reference. And in the above discussion it was stated that the grid frequency was stable and at or very near rated.

Droop Speed Control also describes how a prime mover will respond when the turbine speed reference is stable and not changing but the actual speed (grid frequency) IS changing <b>when the unit is operating at less than maximum possible power output for the current operating conditions.</b> Droop Speed Control is very simple, but touches many aspects of prime mover control and response to various changes in speed and speed reference.

Many people mistakenly confuse frequency control and response with Droop Speed Control. Droop Speed Control describes how much the power output of the unit will change for a given change in the error between the turbine speed reference and the actual turbine speed (grid frequency). The stability of the power output change is not really a function of Droop Speed Control setpoint or regulation; that's more a function of many factors, including fuel control valve characteristics and grid characteristics, but it's not really about Droop Speed Control. Droop Speed Control is really about how much the power output will change for a given change in the error between the turbine speed reference and the actual turbine speed (which is a function of grid frequency).

Yes.

It's that simple. Difficult to describe, because it's really a very "large" concept, but in reality it's very simple.

The best things in life are the simplest, aren't they?

 

An error and a couple of points of clarification.

First, the paragraph:

> And as the turbine speed reference is increased to 104% the load will increase
> to 25 MW, or 100% of rated.

is wrong. It should have read:

And as the turbine speed reference is increased to 104% the load will increase to <b>20</b> MW, or 100% of rated.

Sorry for any confusion the error might have caused.

Now for another form of "confusion."

When a prime mover governor is operating in Isochronous Speed Control, there is nothing the operator can do <b>to the governor setpoints</b> to change the power output ("load") of the Isoch machine. As the number of lights and/or motors and/or computers and monitors ("load") being powered by the Isoch unit increases or decreases the tendency will be for the frequency to decrease or increase, respectively, which means the prime mover speed will tend to decrease or increase.

The Isoch regulator will sense the slight speed change and will increase or decrease the energy (fuel; steam; etc.), respectively, to return the prime mover speed, and generator frequency, to setpoint (usually 100%). No operator intervention required; it happens very quickly and completely automatically.

If the operator were to use the RAISE SPEED/LOAD or LOWER SPEED/LOAD functions to try to increase or decrease the power output ("load") of the Isoch prime mover, what's really happening is the speed setpoint of the prime mover is being increased or decreased which does not change the number of lights and/or motors and/or computers and monitors ("load") being turned on or off.

If the operator were to try to select BASE LOAD on a GE-design heavy duty gas turbine with a Speedtronic turbine control system being operated in Isochronous Speed Control mode, the Speedtronic will ignore the command. The Speedtronic knows that if it switches the control from speed control (Isochronous Speed Control in this case) to temperature control that it would not be controlling speed, and frequency; so, it is programmed to ignore the command.

Same goes for Pre-Select Load; the Speedtronic will ignore the selection if Isochronous Speed Control Mode is enabled and active. It knows to monitor speed (frequency) and only speed (frequency).

The power output ("load") of a machine being operated in Isochronous Speed Control Mode is completely a function of the number of lights and/or motors and/or computer and monitors ("load"), and will automatically increase or decrease the energy being admitted to the prime mover to maintain, very closely, the speed (frequency) setpoint.

The only way to control the "load" (power output) of an Isochronous unit is to, (1) control the number of lights and/or motors and/or computers and monitors in use; or, (2) use a prime mover with its governor in Droop Speed Control Mode, increasing or decreasing the power output ("load") of the Droop unit as necessary to control the load on the Isoch unit. Increasing the power output ("load") of the Droop unit will decrease the power output ("load") of the Isoch unit. But it does nothing to change the number of lights and/or motors and/or computers and monitors. Decreasing the power output ("load") of the Droop Unit will increase the power output ("load") of the Isoch unit. But it does nothing to change the number of lights and/or motors and/or computers and monitors.

Many people confuse "load" and "load."

So, the "test" of Isochronous Control is difficult, at best, other than to say as the "load" (the number of lights and/or motors and/or computers and monitors) increases or decreases the Isoch unit will change the energy being admitted to the prime mover driving the generator and supplying the power to the "load" in order to maintain prime mover speed (frequency).