IGV CONTROL MALFUNCTION

H

Thread Starter

HANYWEPCO

frame-6 GE controlled by TMR Mark-v Control system. while the load was 34 MW on the gas turbine and the IGV was open to about 74DGA and the average exhaust temp. was 567C. then we gradually decreased the load to 30.6 MW and noticed that the exhaust average temp. increased to 580.2, but illogically the IGV ref. signal CSRGV became 62.4. i.e. it is coming down to close more the IGV instead of opening it, which is very strange then the turbine trip on high exhaust temp. spread trip as one sector temp. was actually lower than the others..

any advice or explanation for the reason of IGV control signal of behaving like this.. there was no any change done in the program and the turbine was working before very normal and there is no other abnormal conditions.
 
Hanywepco,

There are several conditions which when satisfied simultaneously will result in a high exhaust temperature spread trip.

Case-1 :
a) Combustion trouble alarm exists (L30SPA): the highest spread TTXSP1 exceeds the allowable spread value TTXSPL (a function of CPD, ambient temperature and mean exhaust temperature) for a minimum 3 seconds

b) The second spread TTXSP2 exceeds 0.8 times allowable spread TTXSPL

c)The two thermocouples giving least readings are adjacent to each other

Case-2 :
a)Exhaust Thermocouple trouble alarm L30SPTA: when the highest spread exceeds a constant which is usually 5 times TTXSPL for a minimum 4 seconds

b)TTXSP2 exceeds 0.8 times TTXSPL

c)The 2nd and 3rd lowest thermocouples are adjacent

Case-3 :
a)TTXSP3 exceeds the allowable spread, which implies TTXSP1 and
TTXSP2 also exceeds TTXSPL

Case-4 :
a) Combustion trouble exists (as explained earlier)

b) One of the R,S T controllers fail

If any of the four above cases exists for a min 9 seconds machine will trip on High exhaust temp spread trip L30SPT

So in your case the machine tripped on what condition?

What is base load IGV opening of your machine? As per MARK's exhaust temp control algorithm, mean exhaust temp TTXM will remain a constant (isothermal) with increase in CPD (compressor discharge pressure)till constant firing temp limit is reached, when TTXM will start decreasing with increase in CPD. When load is increased, CPD will increase since IGV opens to maintain a constant exhaust temp and if your machine is operating in the constant firing temp range TTXM will actually decrease with increase in CPD. Hence when load is reduced, IGV opening reduces and TTXM will increase if the machine is operating in constant firing temp range.

So I believe your IGV behaviour is fine.

Now you did mention that one sector temperature was lower than the other, can you tell which thermocouples were giving lower values?

What were these thermocouple readings when you had taken the machine to 34MW? Were the readings normal?

Well CSA can give us a better insight to this issue. :)
 
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