We have GE frame 6 Mark V control unit that trip on "Comp limit FSR backup control active". This is the last alarm logged on the event view on the unit HMI.

Whereas on the historian we had some other alarms:
"FSR temperature reference active" that comes and clear intermittently as well loss of "compressor discharge pressure bias". I need some explanation on what could caused these alarms and what could be done to avoid reoccurrence of the trip.

Besides we have 3 pressures transmitters that powered R,S, and T processors.

 

Trip due to loss of compressor discharge bias

Sigh, i wish people would at least look at the trip diagram to know what caused the trip before coming here and asking.

well the turbine tripped on "loss of compressor discharge pressure bias". usually if the compressor discharge goes lower than 2.4kg , the trip is activated. the "Comp limit FSR backup control active" and the "FSR temperature reference active" are coming because of the loss in compressor pressure. this loss in compressor discharge can happen due to

A. sudden closing of the IGV
B. Axial compressor failure
c. CDP transmitter or instrumentation failure

check the following signals

A. IGV opening (if it has closed suddenly)

B. hydraulic oil pressure (if there is a sudden drop)

c. Exhaust temperature (if there is a sudden increase in the temp before trip)

d. CDP transmitter (if the value went down then recovered , or it went down and stayed there)

and finally is the compressor working fine now ?? provide more details of the trip so that we can help you better.

 

Your information is less. please provide more information for proper investigation.

please check TTRXB and CPD/CDT at this time .

machine was in FSR bias or CPD bias. running with grid or island mode?

 

Thanks for the reply

Sir asking for more information and support doesn't mean trip log haven't been looked at?

Turbine tripped because the compressor bleed valve opening while unit running at 28MW on the grid. Unit is running on gas and it is CPD biased.

Ok I attached trip history and data on the address below http://www.2shared.com/file/u4yfmN9Y/Trip_history.html

Is it normal that Loss of compressor discharge loss L3TFLT asserted even though the voted CPD pressure is above constant CAKCPD 50psi? by the way the CPD reading in our unit did not drop below CAKCPD.
FSR backup control active is activated because of loss off compressor discharge bias but if my understanding is correct it is not supposed to trip the unit isn't.

>A. sudden closing of the IGV
Yes the IGV started to close my question is why?

>B. Axial compressor failure
No the axial compressor did not failed.

>c. CDP transmitter or instrumentation failure
one CPD out of the three was reading low but the voted was good

>c. Exhaust temperature (if there is a sudden increase in the temp before trip
Info on trip attachment

Thanks for the feedback

 

Turbine Tripping

Abdou you misunderstand me. i was refering to the Trip status in the mark V page. you seem to be guessing what is the reason for the trip. once the machine has tripped the first thing to do is to look at the trip status. here the signal which is responsible for trip will be highlighted in RED. this will make trouble shooting easier. no offense meant. back to the question.

"Turbine tripped because the compressor bleed valve opening while unit running at 28MW on the grid. Unit is running on gas and it is CPD biased."

Though it is a post ignition trip, the trip is applicable only if the GT speed is less than 95%. beyond this only an alarm is announced. the GT does not trip is the compressor bleed valves opens while running. please check your application code to confirm the same. if you were referring to this

-> 12:45:18.687 T3 0 L20CBX EVT Compressor Bleed Valve Control Signal

then L20CBX is the signal to the solenoid controlling the bleed valves. this became zero because L4 went low. so you can discount this , this is not the reason for trip.

"Is it normal that Loss of compressor discharge loss L3TFLT asserted even though the voted CPD pressure is above constant CAKCPD 50psi? by the way the CPD reading in our unit did not drop below CAKCPD."

no, it does not happen as far as i know. the voted value is used in the application code. so if L3TFLT had gone high then the CDP would have gone below CAKCPD at least for one cycle execution.

"FSR backup control active is activated because of loss off compressor discharge bias but if my understanding is correct it is not supposed to trip the unit isn't."

yes, FSR backup control became active due to the reduction in the CDP, but it will not trip the turbine.

Looking at the trip log i cannot definitely say which signal caused the machine to trip. the trip log has no "trip signals" or "trip groups" specified. can you ask the shift personnel and confirm on which signal the machine tripped on ??

I have made the following observations from the trip log. i am uploading the condensed trip log here.

1. In the rows 20 to 23, the IGV had closed form 86 to 56 deg. this is a actual closure of the IGV as the exhaust temp has risen to a very high value of 588. the machine was close to tripping at that time. (604 i believe is the exhaust temp high trip). why this could have happened

a. someone put the IGV in manual control and reduced the setpoint

b. gradual loss of hydraulic oil pressure

c. non responsive servo

were you doing any test at that time like putting the IGV in different control modes?? this seems to have taken place for 3 min. usually for a loss of hydraulic oil pressure the IGV goes on closing reaches 50 deg and trips. this usually happens in a minute or so. check the last chance filter of the IGV moog valve and replace it. after 3 min it seems to have recovered by itself.

2. from 12:44:51 onwards the IGV started closing again. this time also it is a real closing as the exhaust temp is on the rise and CDP is getting reduced from that point.

3. at 12:45:19 machine initiated a trip, but it is not clear which signal initiated the trip.

Can you provide the following details?

a. what is the machine rating at site conditions 30 MW??

b. was there any testing going on at the time of the trip like IGV control ON/OFF??

c. any chance of confirming

is this the full trip log? is there any other details available. with this info i can only may guesses. hope the info i have provided was useful and will get you started in your own analysis. do write back with what you have found.

 

When the bleed valve opens at 30Mw, flow from bleed valve blocks exhaust flow. That yields increasing in exhaust temperature. Then IGV may start to close to decrease exhaust temperature. I can not download the alarm list due to my company internet policies, I don't know what happened exactly.

But I hope the information above will be a bit useful for you.

Regards.

 

> We have GE frame 6 Mark V control unit that trip on "Comp limit FSR backup
> control active". This is the last alarm logged on the event view on the unit HMI.

> Whereas on the historian we had some other alarms:
> "FSR temperature reference active" that comes and clear intermittently as well
> loss of "compressor discharge pressure bias". I need some explanation on what
> could caused these alarms and what could be done to avoid reoccurrence of the trip.

> Besides we have 3 pressures transmitters that powered R,S, and T processors.

=================================
Normally the PCD vs Exhaust temperature curve is on control and FSR temperature curve is acting as a backup. In case of PCD loss "compressor discharge pressure bias" occurs to protect the machine. This means that the temperature control will go on at a lower PCD. But, in addition to that, as you don't have any PCD vs TX curve protection, FSR temperature curve will act as a backup. I would say that the machine has loss the PCD signal or something that can cause PCD loss

Voyager2kbc

 

> When the bleed valve opens at 30Mw, flow from bleed valve blocks exhaust
> flow. That yields increasing in exhaust temperature. Then IGV may start to close
> to decrease exhaust temperature.

Huh? When the axial compressor bleed valves open, it reduces the total flow through the axial compressor, which means less air enters the combustor, which means that if fuel flow remained constant the exhaust temperature would increase. Why would that cause the IGVs to close, because closing IGVs would further restrict the air flow which would further increase the exhaust temperature.

Opening the compressor bleed valves also reduces the axial compressor discharge pressure, which has an effect on the exhaust temperature reference.

We don't know if the original poster's machine has DLN combustors, or what is used as the back-up exhaust temperature control bias--FSR or load (MW). And, it's pretty clear that the original poster's site suffers from an inability to read alarm printout (be it electronic or paper), leading them to believe that the last alarm which might be a trip is <b>THE</b> condition that tripped the turbine. That's quite often NOT the case. It's pretty unfortunate but the sequencing in many Speedtronic panels can annunciate multiple trip conditions after the turbine has been tripped. One has to learn how to interpret the alarm printout.

There's just too little information, but it's pretty clear that someone believes that if the axial compressor bleed valves open when the unit is at Base Load the unit should continue to run without a bobble, and that's just probably not a realistic expectation. At all.

 

Thanks for all the feedback

We have the unit back online running.

Replacement of one of the compressor discharge pressure transmitter clearead the intermittent loss of compressor discharge pressure bias alarm.

You are right Process Value on saying that someone has put the IGV on manual control. Remote operator put the IGV on manual to control exhaust temperature before the trip happened. The posted alarms are all the one captured by the logger. Still unclear on how selecting IGV on temperature control can lead to turbine trip. Because Manual control has authority to command in IGV angle only when less than that called for by the automatic

> a. what is the machine rating at site conditions 30 MW??
Machine usually run around 25-28MW but rating at site condition on base load is 30MW