MARK-V

A

Thread Starter

ALI

We are facing load hunting every winter on one (out of four) GTG; GE-9E, DLN-1 fuel: sweet Gas, control by Mark-V TMR, In operation since 2004.

Hunting is only observed during cold weather i.e temp. <20deg C. load between 75MW and 85MW.

So-far we have tried following.
Replacement of IGV Moog valve.
Replacement of IBH control valve positioner.
replacement of IGV cylinder.
replacement of GCV and SRV moog valves.
All DLN control valve including IGV calibration.
comparison of IBH and IGV control constants with other identical units (found no difference).

For additional information please feel free to contact.

Thanks
Regards,
Ali
 
> Hunting is only observed during cold weather i.e temp. <20deg C. load between 75MW and 85MW.

Hi,

I assume that you mean by 'load hunting' output load oscillations without changing the load setpoint.

Which turbine operation mode is selected at the time of 'load hunting': Preselected load, Part load or Base load?
Is the load of the turbine commanded from outside of MKV i.e. by DCS?
Do you have any process or diagnostic alarms displayed at the time of load hunting?

Assuming that: 'cold weather i.e temp. <20deg C' means: below neg20degC you can consider as one of possible reasons of your issue FSR restrictions by CPR Limit - if this takes place, process alarm should be generated. In very cold days CPR is high due to high density of air. Check calibration of CPD and ambient pressure transmitters. AFPAP indication on all your turbines should be the same.

By monitoring/trending several signals: FPG2, FSG, FAG, FSGR, FSR, FSRN, FSRT, FSRCPR, DWATT, CPD, CPR, AFPAP, CSGV, TNH you can confirm that P2 pressure is stable and gas valve GCV follows requested position (stable servo current) so then you will identify which FSR signal requests for load fluctuation as result of gas valve fluctuation.

Regards
 
Ger73,
Thanks for your reply. You are right in understanding that load is oscillating without change in set-point.

Between 75MW and 85MW cannot be base load for 9E… secondly I couldn’t understand the difference of pre-select and part load. However I can confirm that this occurs when unit is on pre-select load.

Most of time unit is operated from remote (DCS). Nevertheless oscillating in both cases, either control is on local HMI (M-V) or on remote.

There is no process or diagnostic alarm, and ambient temp is <+20DegC. It’s very rare that temp gets below +10DegC at site climate.

There is slight difference of AFPAP i.e. unit under discussion: 151 mmHg, healthy unit: 154 mmHg. I will be glade if you or someone else can explain how AFPAP (indication) can contribute in this issue.

All DLN valves and IGV position feedback are following the demand and servo currents are also reasonably stable and no issue with FPG2 also. But when it starts hunting it’s difficult to nominate single parameter causing this oscillation as all parameters LOAD, Exhaust Temp., IGV, FSR, CPD, CTD and their related parameters starts moving simultaneously.

One thing that I forget to mention last time is that unit is turning to extended lean lean mode on excessive variation.

Another observation that I can share is That, on stable load this unit is having slight more opening of IGV i.e 1.2DGA to 1.8DGA and similar to that more CPD i.e 0.1bar and FSR 2% are also more and conversely TTXM is 3degC less at same load comparing adjacent unit.

I have doubt if wide opening of IGV can result in compressor stalling (surging). Any expert opinion?
 
If possible, Please collect the following real-time value of signals when gt load hunting, and sent the data packets and CSP file to me, I can try to analyze the reasons of load hunting.

my e-mail address: [email protected]
 
And one more thing, the GT with DLN can be running on the the Extended LL mode in a shot time, but it will be reduced the life of the combustor, turbine and other hot path components. so, you should to leave the Extended LL, and back to Premix Stable mode.
 
Hi,

I assumed that your statement: 'cold weather' refers to temperatures below neg 20 degC not below pos 20 degC.

Restriction of FSR due to CPR Limit I have seen for ambient temperatures below neg 20 degC.

CPR (compressor pressure ratio) is the difference between turbine outlet (CPD) and inlet pressure (AFPAP - AFPCS) so wrong calibration of AFPAP transmitters could contribute to the false calculation of CPR. With your clarification of ambient temperature on your site this option as root cause of the hunting should be excluded.

According to GE nomenclature turbine operates in Part Load mode when no: Base Load no: Preselected Load are selected on HMI - you will find such message (i.e. Part Load) on one of the message display windows on the main screen of HMI - please check on your site.

Presented by you difference in calibration of AFPAP transmitters could be one of the contributors to difference in operating parameters between turbines on your site: for calculation of the firing temperature is used CPR parameter (CPD was used on old systems) please see above comment about relation of AFPAP calibration and CPR. The other contributors could be: difference in full stroke of gas valves between the turbines or accuracy in calibration of the IGV (possible presence of backlash). Other contributor could be cleanliness of the compressor part of the turbine.

Several more tags would be advised to trend for ‘hunting’ troubleshooting: TTXM, TTRF1, TNR, L70L and all upstream of L70L, L70RX and all upstream of L70RX, Splitter and Transfer gas valves positions.

You did not write if turbine operates on Premix or on Lean-Lean mode at the instant of the issue: with 75MW load, turbine should be on Premix but this depends on the site settings.

Is this hunting issue a one time wave of load: up and then down or this is sequence of waves (how many? how long time lasting?).
One time wave of load could be the consequence of involuntary transfer from Lean-Lean to Premix. This can happen when turbine operates on Lean-Lean just below transfer point to Premix and then at some instant, TTRF1 passes the transfer point as result of operating parameters fluctuation.

Regards
 
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