Mark V Post Ignition High Pressure Trip

D

Thread Starter

dinster

Friends/Gurus,

350MW, 9FA+e single shaft, Mark V, DLN 2.0+

We experienced difficulties in starting up the machine due to LFPG2HT "P2 POST IGNITION PRESSURE HIGH TRIP". During troubleshooting, we forced open ASV, force closed SRV and observed small passing on SRV side. The Fisher V300 ball valve was replaced last July 2010, so obviously it failed pre-maturely. Unfortunately spare valve will only arrive in 3 months time from now.

The unit tripped approximately 12 seconds after L28FD flame detected while FSRSU is driving the turbine to a Warming period for 1 min before going to Acceleration mode. P2 pressure FPG2 increased beyond tripping limit thus shut the unit down.<pre>
E 14.Feb.2011 06:51:14.188 L4 Master protective signal
A 14.Feb.2011 06:51:14.031 L86FPG2HT_A POST-IGNITION P2 HIGH TRIP
A 14.Feb.2011 06:51:13.469 L30TSVH HIGH SHAFT VOLTAGE
E 14.Feb.2011 06:51:13.250 L3SS_CON Static Starter Connect sequence complete
E 14.Feb.2011 06:51:13.188 L1X Master Control - Startup Permissive
E 14.Feb.2011 06:51:13.063 L43FG_PERM Gas fuel selection permissive
A 14.Feb.2011 06:51:13.031 L3ACS_ALM Servo Control Fault Trip
A 14.Feb.2011 06:51:12.906 L3GRVT_ALM STOP/SPEED RATIO VLV NOT TRACKING TRIP
A 14.Feb.2011 06:51:12.875 L30TSVH HIGH SHAFT VOLTAGE
A 14.Feb.2011 06:51:12.219 L30TSVH HIGH SHAFT VOLTAGE</pre>
1 of the temporary measure suggested was to increase KFPG2HT "P2 POST IGNITION TRIP HIGH SETPOINT" from 42 psi to perhaps 50 psi. Another option suggested was to lower FPKGNO "FUEL GAS PRESS RATIO CONTROL OFFSET" from -31.140 psi to -27 psi to compensate SRV passing rate.

GE has been conservative by suggesting valve replacement and obviously that is not possible at this point of time. Appreciate your valuable inputs especially on the risks / possible other option / etc etc.

Cheers.
 
Dinster,

We are a 9E site and since having TIL 1275 implemented we have encountered numerous problems. We also suffered with the same trip as you. For us, we run a rolling program of changing valves, and whilst it cannot be ruled out, the probability is lower. On one occasion, the root cause of this trip was due to a defective torque converter and hence the machine was not achieving the correct speed. It may be worthwhile checking to ensure that the speed of the machine was not significantly different to previous occasions.

On a more serious note, I would suggest caution in simply adjusting the constants for the alarm. These are here to protect the machine, if these are altered you risk damage to the machine.

On a side issue, we also found that after implementation of TIL 1275 that the constants which set P2 at firing were incorrect and was causing us to fail starts periodically.

Regards

M
 
Check your trip log again for the first out. You did not trip on high post ignition P2 pressure. Your first trip was just over a second before.<pre>
14.Feb.2011 06:51:12.906 L3GRVT_ALM STOP/SPEED RATIO VLV NOT TRACKING TRIP.</pre>
Your SRV valve is not responding properly to the reference, hence the reason for P2 going high.

How high did your P2 pressure go ? What was your SRV valve reference frcrout ? What was the SRV valve position fsgr ? What was the moog current fagr ?

To me 12seconds sounds like a long time from light off to trip. I would suspect a problem with the control of the SRV valve. Has it recently been calibrated, particularly is the null bias within spec ? should be around 0.26mA per coil.
Does the valve respond well to manual position commands. The fischer valves shipped with Mk V drift horribly with age.Is the hydraulic filter on the valve clean.

Does this unit perform a gas leak test upon start up. Are the gas leak test constants realistic. Unless you find a problem, a new valve recommendation from GE doesn't sound like a bad idea. Pointless changing control constant your not going anywhere with a valve that doesn't function properly.
 
G
Dinster, it sounds as if the V-Ball is not correctly centered in the seat when closed (very common), see Fisher instruction manual Form 5290. This requires removal of the SRV from the process, decompressing the actuator spring and adjusting the actuator mechanical stop collars to set the V-Ball stroke on both ends of its travel. The closed end of travel is where the V-Ball is centered per the Fisher instructions. This will require a full valve calibration possibly including adjustment of the RVDT voltage range (not as tough as it sounds). Decompressing the actuator spring is potentially very dangerous if not done correctly!!!! Call with questions.

Greg Ponto
Lead Combustion Turbine Specialist
Elwood Energy
greg.ponto b[at] dom. [dot] com
 
From our Mark V logic, L3GRVT_ALM STOP/SPEED RATIO VLV NOT TRACKING TRIP will not trip the machine (though alarm text showing "TRIP"), this has been verified.

Just before the tripping, following values were captured;

P2 pressure, FPG2 = 3.012 bar
SRV feedback, FSGR = 4.093 %
SRV command, FPRG_INT = -14.176 %
SRV reference, FPRGOUT = 2.146 baR
SRV servo current, FAGR = 47.10 %

During 1 min Warming Up stage, FPG2 should follow FPRGOUT. Slowly within 12 sec, P2 press rising up, therefore Mark V kept telling SRV to close to reduce P2. That explains the difference between FPRG_INT and FSGR. That also explain the initiation of L3GRVT SRV NOT TRACKING TRIP (which in our case set at 5% diff).

Hydraulic filter has been checked and found clean. SRV was last calibrated on Jan 10. After the tripping, we swapped in new servo (valve and actuator remain). But no calibration was done.

Could u pls elaborate a lil bit more on how to verify the null bias healthiness?
 
We have already faced similar problem during start up of our gas turbine last Year. Please calculate the null bias again and put the value in regulator. This may be solve your problem.
 
Dinster,
I am only just reading your post so you most likely have this problem fixed by now - how did you resolve the problem?

Anyways I thought I would share my experience...My site has had similar problem to you...overhauled SRV in Jul 2010, failed the start up P2 pressure test in February 2011. P2 Pressure went above limit and start up failed. At first we thought the V-ball was out of alignment - maybe slightly open at the 0% point so we made a manual adjustment on the actuator to valve linkage. We repeated the start up and P2 pressure was improved so we went for a fired start. Shortly after flame on the unit tripped on guess what - "P2 post ignition high pressure". I put this down to the fact we did the manual adjustment on the ball and did not recalibrate.

In the end we fitted new valve as we were fortunate to have a spare on site. The old valve was found out of alignment and the ball and seat had scores on it hence the reason for failing the P2 start up test.

This was the 3rd failure in 7 years.

There is a valve upgrade that is supposed to be more reliable but requires larger actuator and piping & roofing mods.

Regards.
 
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