The Turbine was in normal operation full speed and suddenly GT speed drop to 50% of the full speed FSR while the FSR in mark IV still 100%, the GT trying to follow the FSR to normal speed but it could not and starting hunting, the operator tries to return the GT to normal speed, but he could not, here what is the reason of this behave?

 

WHAT ALARMS—PROCESS AND DIAGNOSTIC—WERE ANNUNCIATED DURING THE PROBLEM?

What fuel?

What load was the generator at before the problem occurred? Or, is this a mechanical (compressor) drive machine? If the machine is a two-shaft machine does it have variable second-stage nozzles—and if so what we’re they doing when this problem occurred?

The likely culprit is low fuel pressure and/or flow. If the FSR is 100% but the machine power output is low that’s most probably caused by low fuel pressure and-or flow. It could be a problem with the second stage nozzle actuator. If the unit was running on liquid fuel it might be a problem with the liquid fuel pump clutch or the high-pressure liquid fuel pump.

BUT, the best indication of what was happening is the Alarm list. ALWAYS.

 

Fuel NG
Full load
Air compressor drive
Single shaft
Supply fuel normal no issue
System alarm GAG 50% !
No other issue

 

PERFECT PERFECT EXAMPLE of LOOKING AT THE FRIGGIN’ Alarm List—AND sharing the alarm(s) when you POST FOR HELP ON AN INTERNET FORUM!!!

Unless there is something VERY odd happening--which would most likely ALMOST ALWAYS be accompanied by Diagnostic Alarms--OR there is some unusual sequencing without proper Process Alarms to alert operators/technicians/supervisors to problems, someone accidentally set the FSR MANUAL SETPOINT (also known as the FSR GAG setpoint) to 50% from 100%, which would explain why the operator was unable to change the speed/load of the machine.

There is a Display for the MANUAL FSR function. If it's still set to 50%, it needs to be changed to 100% to get things back to a more normal condition.

It is possible that some site-specific sequencing which is activated by an input (probably a discrete (contact) input, or it might be a 4-20 mA input) from an external control system sets the MANUAL FSR SETPOINT (FSR GAG setpoint) to a value of, say, 50%. This would usually be some kind of abnormal or emergency condition detected by the external control system which requires the machine to not increase speed/load above some value (which someone determined would be at about 50% FSR). HOWEVER, GE standard practice is to annunciate a Process Alarm when anything external causes some kind of action as "drastic" as reducing the FSR MANUAL SETPOINT (FSR GAG setpoint) to 50%. So, if there truly wasn't any other process alarm active at the time or prior to the change in the FSR MANUAL SETPOINT (FSR GAG setpoint), then the typical GE standard practice was not followed for some unusual reason. Even if it was something in the Mark* IV that detected a problem and reduced the MANUAL FSR SETPOINT (FSR GAG setpoint) there should have been a Process Alarm to indicate why the change had been initiated/activated.

Best of luck with this one.

REMEMBER THIS: NOT EVERY GE FRAME 5 HEAVY DUTY GAS TURBINE IS LIKE EVERY OTHER GE FRAME 5 HEAVY DUTY GAS TURBINE. WHEN YOU'RE ASKING STRANGERS FOR HELP IT'S ALWAYS BEST TO PROVIDE ALL THE INFORMATION YOU CAN TO GET THE MOST CONCISE HELP AS QUICKLY AS POSSIBLE--THIS INCLUDES PROCESS- AND DIAGNOSTIC ALARMS!!!! IT'S IMPOSSIBLE TO STRESS THIS ENOUGH: LOOK AT THE FRIGGIN' ALARM DISPLAYS (PROCESS AND DIAGNOSTIC) WHEN TROUBLESHOOTING PROBLEMS LIKE THIS, OR EVEN SIMPLER ONES, AND CERTAINLY MORE DIFFICULT ONES. AND, WHEN WRITING FOR HELP FROM TOTAL STRANGERS ALWAYS PROVIDE ALARM INFORMATION!!!

FULL STOP.

PERIOD.

Personally I have never seen anything like this in a SpeedTronic Mark* turbine control system (driving MANUAL FSR SETPOINT (FSR GAG setpoint) automatically to some preset value). Usually MANUAL FSR is ONLY used for testing purposes or to limit output for some unusual reason--and it's activated from the MANUAL FSR display (or the FSR display on newer machines with HMIs) by an operator. So, this is an unusual--at least for me--situation. (And it sounds like for the site as well.)