Dear Friends,

My Question is

When the Turbine reach Temperature control it is almost on or very near to Base Load and the TNR must read almost 104 % on a Turbine with Droop control

What if the the turbine goes to 105% TNR with temperature control Base Load selected. Can it be a Peak Load I have controversy over this issue with one of site

Cheers
Mambo

 

Mambo,

No. Someone's been mucking with the Droop Constants, and/or the ambient is lower than normal.

Have you checked the calculated TTRX versus the Control Constant values running in the Speedtronic turbine control panel?

Inaccurate GCV LVDT calibration can also contribute to this problem.

 

Dear CSA,

Thanks for your quick response.

For further information I have noted the following settings and parameters with unit on load.
Its Frame 6 GE Gas Turbine, combined cycle,gas fired only

CTIM = 26 DEG C, DWATT = 31.8, FPG2 = 20.09 BAR
FPG3 = 23.58 BAR, FSG = 73.73%, FSGR = 33.89%
FSKRN1 = 14.70, FSKRN2 = 13.0%/%, FSKRN3 = 1.0%
FSR = 73.54%, TNH = 100.02%, TNR = 105.02%, TNH_RPM = 5116

TTRX = 551 DEGC, TTXM = 551 DEGC, TTRXP =551 DEGC
TTRXB = 551 DEGC, TTRXS = 574 DEGC, CSGV = 86Dga

TTK0_C = 8.95 BAR, TTK0_I =568 DEGC, TTK0_K = 76%
TTK0_M = 2.42 C/%, TTK0_S = 15.43C/BAR

TTK1_C = 9.78 BAR, TTK1_I =593 DEGC, TTK1_K= 61.6%
TTK1_M = 2.27 C/%, TTK1_S = 14.99 C/BAR

TTK2_C = 9.17 BAR, TTK2_I =568 DEGC, TTK2_K= 76.0%
TTK2_M = 2.42 C/%, TTK2_S = 15.99 C/BAR

GCV and SRV LVDT'S were checked and calibrated to perfection.

FPRG = 20.02 BAR, FPRGOUT = 20.02 BAR
FSG = 73.63, FSR = 73.54, FSROUT = 73.54

Kindly advice further.

Cheers
Mambo

 

Mambo,

There are just too many intangibles to say for certain why the TNR is so high. Inlet air filter cleanliness/differential pressure; IGV cleanliness; axial compressor cleanliness; exhaust duct back-pressure; turbine nozzle condition; turbine clearances; fuel characteristics (heating value change); etc.

Also, are these the Control Constants from the Control Specification, or the Control Constants in the running Speedtronic turbine control panel?

An IGV angle of 86 DGA would imply that a modification was done to the turbine--including a modification to the exhaust temperature reference control curve parameters. That would also imply that there is a Control Specification that was provided with the new IGV angle modification with the appropriate exhaust temperature Control Constants.

And, who said the machine had a 4% droop? While most gas turbines do have 4% droop, some don't.

Does the unit have Peak Load Capability?

What does the display say when TNR is at ~105%: Base Load or Peak Load?

A turbine in new and clean condition, with clean inlet air filters, at or near design exhaust duct back-pressure, at or near nameplate ambient conditions and with the fuel characteristics as specified when the turbine was originally built and installed and commissioned and with 4% droop will reach Base Load at a TNR of approximately 104%. This also presumes OEM parts and adherence to OEM maintenance practices and procedures.

If the fuel characteristics have changed (lower BTU content) then it may take more fuel flow--hence a higher TNR--to achieve the firing temperature defined by the exhaust temperature control curve.

If the maximum IGV operating angle was changed without accompanying changes to the exhaust temperature control curve then it's very likely that more fuel will be required to achieve the same exhaust temperature control because of the increased air flow through the machine--and the power output would also increase. (All of this would also have an affect on hot gas path parts life--probably not good.)

The formula for TTRX is in several control.com threads, as well as in the Control Specification and the CSP (I presume it's a Mark V). So, it should be possible for you to calculate the exhaust temperature reference for the operating CPD and compare it to the Speedtronic value. Again, it's anybody's guess as to what Control Constants should be in the machine at this point.

As for droop; it's not about the TNR at Base Load. It's about how much power output changes for a given change in TNR--again presuming the turbine is in a new and clean condition, the inlet air filters are clean, fuel is per specification, etc., etc. It general, a machine with 4% droop <i>should</i> change power output by approximately 25% of rated for each 1% change in TNR--presuming everything is as it should be.

And there's just no way for us to be able to tell what the condition of anything is at the site.

 

Dear CSA,

Thank you very much for explaining my question.

This parameters are after a Major Overhaul with new sets of Air Inlet filters, all new super seeded IGV blades, and all as good as new HGP components includes refurbished rotor with new sets of compressor blades.

BTU of gas was very low to 650-700, internal trims of gas valves specially engineered and replaced, all new servo and lvdt's placed, all new fuel nozzles designed for this project. it is a 1995 built GT.
The control constants set are near to Original as provided. Compressor is pumping out almost 9.8-10.0 Bar @27 Deg ambient, ambient can reach upto 40 deg max

There is no indication of Peak load when we cross 105 TNR, turbine shows Base load with Temperature control.

There is Peak load selection here on GE MKV but operations have never tried to run on Peak load.

Controversy started with TNR crossing 105 and I thought we reach peak load which is not a good mode of operation, in this case we are at risk with hot summer days approaching we may see high exhaust temp. soon.

Presently I will review again the specs and settings as mentioned by you.

Any further suggestions

Thanks for all your help and Info.

Cheers
Mambo

 

Mambo,

So, this is the machine you wrote about some time back....

LOTS of changes--and the most relevant to your original post in this thread are the changes to the gas valve internals and the fuel nozzles, with no mention of any changes made to P2 pressure reference or FSR constants (Firing; Warm-up; FSNL; etc.).

It would be reasonable to assume that with such a major change to the gas fuel make-up and gas valve internals that some corresponding changes would necessarily need to be made to several gas fuel-related Control Constants in order to achieve similar operating characteristics (in particular, Droop).

I suppose that there is no data from operation during a time when the gas fuel was at or nearer to original specification, particularly what FSRs were at FSNL and at Base Load, and what was TNR at Base Load when ambient conditions were near rated.

You have also not told us if you had to make any changes to Firing or Warm-up FSR, or FSNL FSR. When the unit is on speed control (which it is from FSNL to Base Load) the Speedtronic is going to put as much fuel into the machine as is necessary to achieve the operation defined by the parameters. If you had to make a significant change to FSNL FSR to get the machine to be closer to approximately 100.3% speed in order for automatic synchronizing to work better, that will have an affect on the droop characteristic. If you had to increase or decrease Firing FSR or Warm-up FSR after the outage that would also point to a need to review and possibly calculate new fuel Control Constants in order to maintain 4% droop.

But, it's just not reasonable for so many hardware/mechanical changes to be made without some corresponding Control Constants to need to be changed to maintain prior operational characteristics. (One more change you didn't expound on: what was the maximum operating IGV angle before new IGVs were installed: 84 DGA or 86 DGA?)

 

Dear CSA,

Yes, the same machine. They have very low fuel BTU Gas being used around 650-700 btu.

At that time they used FSKSU_FI = 17.5 %, FSKSU_WU = 14.4 % and FSKSU_AR = 33.0 these constants are the same after the major overhaul done.

P2 pressure was changed from 17.5 to 20 Bars by changing value of FPKGNG and FPKGNO,

Temperature constants remained the same. Speed constants were same

FSKRN1 ans FSKRN2 as 14.7 and 14,

FSR at fsnlwas noted at around 21% . This change noted is due to change in the internal trims changed.
I think these fuel firing FSR needs to be changed to lower settings.
TNH(speed) at FSNL noted was 99 % and after synchronizing it reads 100%,(5014 rpm steady) I think is due to match voltage and frequency with grid.

IGV angle changed from 84 to 86DGA, was due to give more air as new P2 pressure is increased.

These settings were done by engineering company hired to do this job. But now there are few questions raised about this TNR issue I need to think from the maintenance point of view. I also think the the temperature TTXM is bit higher side.

Please advice further

Cheers
Mambo

 

Mambo,

The "reasoning" used to describe the maximum IGV operating angle change and P2 pressure reference change is ... questionable, at best.

If the unit is using "straight" Droop speed control, and you observe the FSR at FSNL to be 21% and the FSNL FSR is set to approximately 14, that seems to be a bit of a problem.

If the unit is not having trouble establishing flame and warming up with the current FSR values then what's the need to change them?

If TNH at FSNL is 99.0% before synchronizing then it's most likely related to the low FSNL FSR value, and it is also likely similarly affected (though not as much) by the gas valve trim changes and the fuel nozzle orifice changes.

TNH after synchronization to a grid of any size is directly proportional to grid frequency. If grid frequency is at or near rated, then TNH will be at or near 100.0%, and will vary as grid frequency varies.

I don't have access to any Mark V/VI documentation at this writing but if I recall correctly FSKRN2 is the Droop Speed Control "Gain" constant, and FSKRN1 is the Droop Speed Control "Offset" (also called FSNL FSR). I believe you will find that if you increase FSKRN1 to approximately 20%, while the unit is near FSNL, that TNH will start to increase closer to 100%.

READ THE ENTIRE DESCRIPTION BELOW BEFORE MAKING <B>ANY</B> CHANGES, FOLLOW THE INSTRUCTIONS EXPLICITLY AND REPORT THE RESULTS AS REQUESTED.

Please report back the results (how TNH changes when you ONLY change FSKRN1 while the unit is near FSNL). [Do not use the RAISE/LOWER SPD/LOAD targets to change speed while making this change to FSKRN1. You want to change FSKRN1 only, and you want to get TNH to be just slightly higher than 100.0% (say, betwee, 100.1% and 100.3%)--but it's not CRITICAL to adjust it perfectly. TNR should be at, and remain at, approximately 100.3% if the offline speed setpoint Control Constant is set correctly (it's TNKRn, where 'n' is an integer from 0 to 7). Again, do NOT use any manual value to change TNR while adjusting FSKRN1 to make TNH equal to approximately 100.1-100.3%.)]

Then, please tell us what the values of FSR and TNR are at Base Load <b>BEFORE</b> you make the change to FSKRN1, and then what the values of FSR and TNR are at Base Load <b>after</b> you make the change to FSKRN1.

(I predict you will find that after you adjust FSKRN1 to get TNH closer to 100.1-100.3% that you will find that TNR at Base Load will be closer to approximately 104%--if you follow the instructions explicitly.)

 

Dear CSA,

Thanks for the reply, I have taken notes of your informations and will try to collect data at the first opportunity available. presently unit is running on full load with constants TNKR2 = 100.3 %, TNKR7 = 100.2%, turning gear ratio 5114/3000,, KTNH_GAIN = 51.14/%

I will keep you updated

Cheers
Mambo

 

Mambo,

<b>None</b> of the Constants you mentioned have anything to do with the issue under discussion.