After newly start up, at around 50 MW during load increasing our GT Mark VI FUEL CONTROL DISPLAY goes in "LOAD LIMIT". Does anyone here can explain to me what is this "LOAD LIMIT".

Usually this FUEL CONTROL DISPLAY must be DROOP_SPEED or TEMPERATURE during base load operation. L30F_DWCK = LOAD LIMIT CONTROL? Is this the one referring to the FUEL CONTROL DISPLAY? Or there is another source of this LOAD LIMIT?

I checked the FSRV2 block (Fuel Stroke Reference) shows that L30F_DWCK is coming from L30FCTD = Compressor discharge temperature control indication. How can I know the setting for this?

What this LOAD LIMIT DISPLAY really do in our GE GT unit? What parameters must I check during this LOAD LIMIT?

Thanks.
JM

*note: BASE LOAD CAPABILITY approx 235 MW.

 

Are there any Process- or Diagnostic Alarms which might be indicative of some condition or situation which has been detected which is preventing the unit from being loaded?

Any load limit would likely prevent the turbine speed reference from being increased. Most GE-design heavy duty gas turbines are loaded using Droop Speed Control below Base Load, and to change load the turbine speed reference must be changed.

The usual signal name for the logic which increases the speed reference is L70R, and there are several signals (L70RX1, L70RX4, etc.) any one of which will pick up L70R to increase the speed reference, which would cause the fuel to increase and the unit to produce more torque, and accept more electrical load.

I'm not familiar with this specific signal name or control scheme, but if it were me, I'd start working backwards from L70R in the .m6b file using Toolbox to try to find out which auxiliary raise logic is being "blocked" from raising the turbine speed reference, and then what is causing the blocking.

Having said the above, CIMPLICITY displays are very difficult to decipher, especially when they are "enumerated data" displays (which this one sounds like), which takes an analog value and then "converts" it to a text string (that's not a good explanation, but it's the best possible in a short period). Also, CIMPLICITY displays have been known to have lots of problems, especially these enumerated data field displays. If everything isn't configured just right, then the wrong message can be displayed, or perhaps the text string wasn't edited or written correctly.

Hope this helps.

Have you considered asking the packager of the GE-design heavy duty gas turbine for help with the issue? Is it the unit still under warranty?

Or, if you work for GE or are a contractor for GE, have you opened a PAC case?

 

I called a former colleague and he looked at some old .m6b files he had (I don't have a copy of Toolbox these days), and apparently there was some logic in the F-class units that, when they detected a problem with load transducer feedback would "freeze" FSR to limit the load. FSR is "clamped" to FSRDWCK.

And, it seems, instead of blocking L70R the programmers "froze" FSR, which is completely against typical GE-design heavy duty gas turbine control philosophy, they implemented the "load limit" by freezing FSR.

I guess the definition of typical has been expanded.

We didn't get to talk very long so all of the above is from a very quick and brief conversation and a second-hand review of an .m6b file, but there should be a Process Alarm to indicate the problem. My guess is that if all the transducers are indeed working properly, a Master Reset would likely allow continued loading, but that's just a <b><i>guess</i></b>, based on the fact that the Master Reset function has been repeatedly misused in recent years.

 

From what I understand - FSRDWCK (FSR for MW fault) comes from L30F_CTD. Also L3DWBCOKZ would directly be linked to FSRDWCK i.e. if after generator breaker closure, load is less than 2.0 MW for over 5 secs than MW transducer not okay would be annunciated which would latch FSRDWCK (Value for FSKDWCK is 30%)and the FSR value would get locked at 30%.