In my site we are facing a problem with gas turbine. The turbine cannot reach “COMPLETE SEQUENCE”. It stops at speed 90% (HP shaft), and the minimum operating speed for complete sequence is set at 95%.
I noticed that on the <I>, when the turbine is at 90%, the active FSR control loop is the START UP control loop. This means, this loop is limiting the fuel gas to the turbine which results in speed limitation to 90%.

I checked this control loop on the CSP, in the BBL, FSRSUPV1 startup FSR and I found the FSR is limited by the parameter FSKSU AR which set as constant at 31.9%.

For your info, the machine is MS5002C (TWO SHAFT MACHINE) which drives centrifugal compressor with Mark5 control system.

 

saha,

The first question to be asked is: What has changed? Why is the unit now experiencing this problem, because it's likely that it didn't have this problem in the past (a Mark V with an <I> is pretty "mature" (a polite way of saying it's getting older)).

Has the fuel supply changed? Is the BTU content of the fuel less now that previously? What fuel is being burned?

If the unit is burning gas fuel, is the gas fuel supply pressure normal and stable? Is the SRV working properly? Is P2 pressure normal? Have the GCV LVDTs recently been "calibrated?"

If the unit has variable second stage nozzles, is the nozzle actuator working properly?

What Process- and Diagnostic Alarms are active? (Please list all alarms--even if they don't seem related to the problem.)

How long since the last maintenance outage?

Is the axial compressor clean? Are the inlet air filters clean?

Has the operation of the centrifugal compressor driven by the turbine changed recently? Is the compressor more heavily loaded during starting than before? Are the centrifugal compressor valves working properly?

Yes; FSKSU_AR could be limiting the amount of fuel, but if the turbine wasn't having problems before but it is now then adjusting FSKSU_AR isn't going to solve the root problem--and at 31+% it's already pretty high and could result in so much fuel flowing that the unit reaches exhaust temperature control which is not good for the turbine and could also cause failure to reach rated speed.

So, discovering and solving the root problem(s) is the proper way to fix this problem--not just by changing the Control Constant. If the unit hasn't been serviced in a while, the fuel nozzles or fuel system components could need refurbishing. If something has changed in the way the unit is being operated, then that should be factored into the decision. If the fuel has changed, then that should be considered. The fuel system (natural gas or liquid fuel) should be reviewed and all components should be confirmed to be clean (especially all filters and strainers!). A variable second-stage nozzle actuator should be verified to be working correctly and it's LVDTs should be verified to be calibrated correctly.

Please write back with the answers to the above questions, and with the results of any troubleshooting and to let us know how you resolve the problem.

 

CSA,

I definitely agree that something has changed. This unit would have variable 2nd stage nozzles - I don't know of any 5002A, B, C or D or later machines that don't have this feature.

I doubt that any change in the compressor load would prevent the HP shaft from reaching 100% speed. The 2-shaft gas turbines are usually tested at the factory with the LP rotor locked and the HP set gets to 100% speed easily.

 

The MKV is capable of Manual FSR.

 

> The MKV is capable of Manual FSR.

CuriousOne,

Manual FSR can be used to decrease FSR, but not to increase it. From the information provided, it would seem FSKSU_AR is limiting the fuel for some reason. Either there is a flow restriction in the fuel supply (plugged filter and/or strainer; decrease in fuel heat content); some problem with the Gas Control Valve LVDT calibration. I also have to wonder if there's some problem with the second-stage nozzle control or actuator that's sending too much hot combustion gas to the LP turbine, starving the HP of needed torque.

Hopefully the original poster will write back with more details.