Can any one tell me please, the possible cause of unit tripping at 94% FSNL. ours is Gas turbine frame 6B.

The following action had been taking with no success:
Compressor air filter clean, discharge pressure at
55bar. thermocouple checked found okay, spark plug changed.

Regards.
Dottey

 

Dottey,

Thanks for telling us what you've done to try to resolve the problem.

You didn't tell us when this problem started, like after a maintenance outage, when the fuel valve LVDTs might have been "re-calibrated", or some other event.

But,

<b>You have to be joking, right?</b>

You haven't told us what Process Alarms are annunciated at the time of the trip. (<b>EVERY</b> trip is supposed to have a Process Alarm to tell the operator why the unit tripped) and what Diagnostic Alarms are annunciated prior to and after the trip?

The <b>first</b> thing to do whenever a turbine is tripped (emergency shutdown) is to review the alarm printout and determine what caused the trip and then resolve that problem. That includes looking at all the Process Alarms that were annunciated prior to the trip and during the start/acceleration or when the unit was running to determine if there was some clue there that the unit was about to trip.

I've never seen a dirty compressor inlet air filter prevent a turbine from starting, but I guess it could happen in some very bizarre circumstances (which would include some very poor operating practices).

An axial compressor discharge pressure of 55 bar would probably not allow the unit to reach FSNL as that would represent a pretty damned high backpressure.

You say you checked "the" thermocouple (singular) and "it" was okay. Which thermocouple? There are probably at least 18 T/Cs in the exhaust, 12-14 in the wheelspaces, two in the axial compressor discharge, and so on.

You just haven't provided very much in the way of useful information, or even correct information. If I wrote to you and asked if you could tell me why the light in my room wouldn't go on when I closed the switch and I said I had changed the sheets on my bed and swept the floor and made sure the window shade was down, how would you reply?

And changing the spark plug would have <b>absolutely <i>ZERO</i> effect</b> on tripping at 94%--because it's de-energized a minute or less after it's energized! It's not necessary for turbine operation except for establishing flame and then the flame is continuous as long as there's sufficient fuel and air--and a run permissive. A combustion turbine is not a gasoline reciprocating engine that requires a spark to ignite the fuel after every compression stroke.

This must be a joke.

It's a joke, right?

(I hope it's a joke.)

Presuming it's not a joke, if the only alarm that's being annunciated is "Loss of Flame Trip" then it's likely there's something wrong with the fuel supply, or the wiring to the fuel trip solenoid, or the IGV solenoid, or the relay driving the trip solenoid output, but there should be alarms (Process or Diagnostic) to provide some indication there's a problem. Like low gas fuel supply pressure, or low liquid fuel supply pressure. If it's a Speedtronic issue, then there would likely be Diagnostic Alarms alerting the operator to some kind of problem.

And if there are <b>no</b> alarms (which is extremely unlikely) then it's likely an electrical/circuit problem. It would also be helpful to know if there is an existing 125 VDC battery ground alarm. Because that can play havoc with lots of things.

Also, has any 125 VDC solenoid been replaced lately (like the Compressor Bleed Valve solenoid, 20CB-1). Does field flashing start at 94-95% speed?

But if it's always occurring at approximately 94-95% speed, then it's probably something associated with an "event" that occurs just prior to or just after 14HS .

But, seriously, Dottey, you gotta provide more information than you did. Including which Speedtronic you're using. You didn't tell us if the start-up and acceleration was normal, or if it's longer than normal, or shorter than normal. Were the flame detectors flickering and was there high exhaust temperature spreads?

But, hey--that was kinda funny about checking the air filters and changing the spark plugs on a gas turbine!

Kinda.