we have SRV in GE frame 6 gas turbine with markv and HMI. at full speed no load the SRV valve open only 10% so the color for this valve not changed to green color.

is there any relation for P2?.
or i have the vent valve between SRV &GCV?

 

8784597,

The SRV tries to control the pressure between the SRV and the GCV. To know if it's working correctly, check FPRG and FPG2--they should be equal. And if FPG2 is equal to FPRG, then the SRV control is not the problem.

If they're equal then it sounds like the fuel gas supply pressure is very high, because if that's high then the SRV doesn't have to open very much to make the actual P2 pressure equal to the reference. You need to remember that as load increases the SRV will open more to maintain the same P2 pressure.

When I've seen this problem before it's because the fuel gas pressure is excessive.

As for the valve color not changing to green, that could be the result of one of a couple of things. Many times the CIMPLICITY display can be configured not to change color until the valve position is above a setpoint which is defined in CIMPLICITY. Or, there could be a logic signal generated in the application code that changes state based on a Control Constant. In both cases, it's just necessary to change the value of the setpoint--but you must first determine if the position comparison is done in CIMPLICITY or application code.

It could be a combination of the two--an excessive fuel gas supply pressure and an incorrect position comparison setpoint.

Please write back to let us know what you find.

 

where i can find FPRG?

 

rwailikhalid,

FPRG is a control signal database signal name for P2 Pressure Reference (Fuel Pressure Reference-Gas).

You can add it to any User Defined or Demand Display, or you can display it on a Logic Forcing Display (it's not forceable, but it can be viewed on the Logic Forcing Display). It can also be found on the Prevote Data Display.

But, it's probably not on any CIMPLICITY display (presuming the site uses a GE Mark V HMI running MS-Windows and CIMPLICITY).

 

From demand display, I get the reading for FPRG and it was -2.76 at zero speed. It is the same for FPG2. In constant display the constant KFSGR was 10% in R and 2.5 in both S, T processors. I changed them to 2.5 for all.

Start the turbine and after firing the SRV color changed to green at 2.5 % of SRV open stroke. At 92.3 % of speed the SRV not open more than 5.5 % and the speed not increased more.

FPRG at this speed was 13.9 and it the same for FPG2.

Why the speed not increased more than 92.3 %? Is the SRV need to open more than for more gas or what? Is there any problems in the S/W ?
With two attempts of starting, I get the same.

 

12542654/rwailikhalid,

This is frustrating--I'm sure for the both of us.

You are mixing two "related" but separate issues. You are overly concerned about the color of the SRV on a display, and seem to have solved that problem by changing KFSGR. The fact that you found the value different in <R> from the other two processors is also very troubling--to me--but that's another issue I don't want to go into in this thread.

If FPG2 was equal to FPRG at 90+% of speed, then the SRV is open as much as it needs to be. I presume the units are barg--not psig. 13.9 barg would be about 201.6 psig which would seem to be a reasonable value for P2 pressure (FPG2) at about 90+% speed. So, if the gas fuel supply pressure is really high then the SRV might not need to open very much.

But I strongly suspect the calibration of the IGV LVDT(s) is very, very incorrect. The good news for you is: SRV LVDT calibration doesn't need to be very accurate; in fact, it can be very, very bad, and the unit can still continue to run--as you're very likely finding out. The regulator for the SRV (the regulator is the control element that decides what "position" the SRV should be in) is a pressure control loop--because it's trying to control P2 pressure (FPG2) to be equal to P2 pressure reference (FPRG) which is a function of turbine speed. The regulator will put the SRV at whatever position it needs to be at in order to make the actual P2 pressure (FPG2) be equal to the P2 pressure reference (FPRG)--whether that's at 5.5% of SRV opening, or 10% of SRV opening or 25% of SRV opening, and regardless of the calibration of the SRV LVDTs, meaning that even if the LVDTs are "calibrated" such that the Speedtronic thinks the SRV is at 5.5% opening ("stroke") and it's actually at 14.7% stroke (as indicated by physically looking at/measuring the valve position) it will put the valve at the position required to make actual P2 pressure (FPG2) equal to P2 pressure reference (FPRG) for the current turbine speed.

And, contrary to popular belief the SRV <b>does NOT</b> go to 100% stroke when the turbine reaches 100% speed. The valve will be placed at the position required to make the actual P2 pressure (FPG2) equal to the P2 pressure reference (FPRG) for the speed of the turbine and the flow through the gas valve assembly. (As flow increases the P2 pressure would tend to decrease (when at 100% speed), but the SRV regulator will increase the SRV opening to keep FPG2 to FPRG as the GCV opens. As the GCV closes (when at 100% speed) the P2 pressure would tend to increase--but the SRV regulator will decrease the SRV opening to keep FPG2 equal to FPRG. And, that's "real" SRV position--regardless of what the LVDTs are "calibrated" to indicate.)

Now, if there's 13.9 barg upstream of the GCV and the unit can't make rated speed, then something else is wrong. I strongly suspect there are Process- and Diagnostic Alarms you are not reporting, and which would be very helpful in troubleshooting and resolving this--new--issue, because before you were only worried about the valve color on the display (which has NOTHING to do with turbine operation, as you reported previously when you said the color didn't change until indicated position was greater than 10% even though the turbine was at rated speed). So this inability to reach rated speed should not be related to valve color on some display.

Gas fuel supply pressure should not ever be more than approximately 20 barg, because the gas valve assembly and flanges are only rated for about 20 barg. If the gas fuel supply pressure (upstream of the SRV) is high--higher than 20 barg--that could explain why the SRV isn't opening very far to get FPG2 to be equal to FPRG.

But the thing you're NOT telling us is: What is the actual physical position of the SRV when the unit is at 90+% speed? Is it really only at 5.5%--<b>OR</b> (more likely) is it at 12% or 15% or 20% (presuming gas fuel supply pressure is more in the range of approximately 17 barg--which is what it should typically be).

However, if the pressure upstream of the GCV is in fact 13.9 barg, then there should be sufficient pressure/flow through the GCV for the turbine to reach rated (100%) speed. Something is not allowing the GCV to open far enough for the amount of fuel passing through it to make the turbine accelerate to rated speed. <b>AND</b> if the GCV is not opening far enough then that could explain why the SRV isn't opening very far--because there isn't sufficient flow (through the GCV) to make the turbine accelerate to rated speed.

Now, the most likely cause of the GCV being "limited" is that the actual average exhaust temperature (TTXM) is exceeding the exhaust temperature control reference (TTRX)--usually about 1100 deg F (593 deg C). If the actual average exhaust temperature (TTXM) exceeds TTRX during acceleration then the GCV is prevented from opening and increasing the exhaust temperature any further.

So, the most likely problem is that there is--for some reason--a problem with unusually high exhaust temperature(s) in the gas turbine exhaust. This is usually caused by high exhaust temperature spreads (differential readings between the numerous exhaust thermocouples) that result in an erroneous average exhaust temperature. Or, there are physical problems with the exhaust thermocouples. Or, exhaust thermocouples have been jumpered together that shouldn't be jumpered together and this results in high spreads and erroneous average exhaust temperatures.

Finally, sometimes, there mechanical problems with the axial compressor and/or the turbine and/or the inlet air filters and/or the calibration of the IGV LVDTs that can cause the air flow through the turbine to be much less than normal during starting and that can cause exhaust temperatures to be abnormally high--and that can cause the GCV to be prevented from opening sufficiently to reach rated speed. A dirty or worn axial compressor can also contribute to this problem. Or, IGV problems (individual IGVs broken or bent). Anything that prevents normal air flow through the turbine can cause elevated exhaust temperatures. If it's been a long time since the last turbine maintenance outage, this can also cause problems (high internal clearances; nozzle/bucket problems; etc).

So, there are several things to look at and investigate. But, it's extremely unlikely that failure to reach rated speed is caused by SRV position <b>based on the information provided.</b> And, always, when you suspect the indicated values on any display are not correct, then someone needs to go out to the turbine and check gauges and scales to see if the reported conditions are real--or not. In the case of the SRV, there is almost always a graduated scale, a round brass bar with red lines on it which are marked in 0.050 inch increments (every thick red line usually is 0.250 inches and there are usually four thin red lines between each thick red line) and a pointer on the bar attached to the SRV valve stem which can be used to measure actual SRV position without using a dial indicator or calipers. One cannot always trust values on a display, and if they are in question then one must somehow verify--and there are almost always gauges or scales for this purpose on every GE-design heavy duty gas turbine.

Please write back with your findings. Specifically, tell us about the alarms being annunciated as the turbine is being started (and those which are active before the turbine is started). Tell us about the values of TTXM and TTRX during starting--and if they are equal before the speed starts to level off below rated speed. Tell us about the GCV position (FSG) and the value of the GCV reference (FSR) during the time the speed is near rated but not increasing. And tell us what the gas fuel supply pressure is--upstream of the SRV. And, tell us what the actual physical position of the SRV and GCV are at the time the turbine speed begins to level off at less than rated speed. Also, what is the IGV angle (indicated--from the display--and from the pointer on the compressor casing in the Turbine Compartment). And, tell us about the exhaust temperature spreads: TTXSP1, TTXSP2, and TTXSP3. We will need that information if we are to be able to help you.