MK-6 Gas Turbine Frequent Tripping

M

Thread Starter

Mufeed_99

We are having a GE Frame 5, with Mark-6 HMI that has been tripping frequently due to unknown reasons. We observe from the MK-6 HMI, data values before and after unit shutdown.

Prior to Gas turbine shutdown, we observe the following: -
1. The FSG - GCV position command was 41.1943 and Feedback signal is 40.8317%. The FSROUT – GCV position reference command was 41.8629 and Feedback signal was 41.7574%.

2. The CSGV - IGV position command was 84.1362 and Feedback signal is 83.2053%. The CSRGVOUT – IGV position reference command was 85 and Feedback signal is 85%.

3. The FSGR - SRV position command was 22.9643 and Feedback signal is 23.5279%. The FRCROUT – SRV position reference command was 23.4037 and Feedback signal is 24.062 %.

After Gas turbine shutdown, we observe the following: -

4. The FSG - GCV position command was 41.1943 and Feedback signal is –4.92371%. The FSROUT – GCV position reference command was 41.8629 and Feedback signal was –25%.

5. The CSGV - IGV position command was 84.1362 and Feedback signal is 42%. The CSRGVOUT – IGV position reference command was 85 and Feedback signal is 42%.

6. The FSGR - SRV position command was 22.9643 and Feedback signal is –4.9927%. The FRCROUT – SRV position reference command was 23.4037 and Feedback signal is –5.0%.

The Alarms that were generated by the MK-6 HMI are:
21-June-2008 08:47:02.936 G1 0Q 0162 ALM INTERSTAGE PRESS. SENS. EXC. SPREAD ALARM
21-June-2008 08:47:03.058 G1 1Q 0064 ALM SEISMIC VIBRATION DIFF. TROUBLE ALARM
21-June-2008 08:47:03.096 G1 0Q 0064 ALM SEISMIC VIBRATION DIFF. TROUBLE ALARM
21-June-2008 08:47:03.702 G1 1Q 0162 ALM INTERSTAGE PRESS. SENS. EXC. SPREAD ALARM
21-June-2008 08:47:06.772 G1 0Q 0162 ALM INTERSTAGE PRESS. SENS. EXC. SPREAD ALARM
21-June-2008 08:47:15.578 G1 1Q 0162 ALM INTERSTAGE PRESS. SENS. EXC. SPREAD ALARM
21-June-2008 08:47:17.840 G1 0Q 0162 ALM INTERSTAGE PRESS. SENS. EXC. SPREAD ALARM
….

We have been suspecting following items below, which were also attended by doing good Preventative Maintenance during this shutdown:

1. Lube Oil System and Hydraulic system problem
2. SRV is not working properly
3. Dumping valve is not working well

We would like to have some opinion on this problem, and how we shall resolve it to restore the gas turbine operation.

Regards
 
We are presuming the unit has a TMR Mark VI (you didn't say; it would be helpful to know) and multiple P2 pressure sensors (it would be extremely helpful to know how many P2 pressure sensors are in use on the unit).

You need to look at the P2 pressure sensor sequencing and monitor the feedback from the P2 pressure sensor(s). You need to determine if the excessive pressure spread alarm existing for "too long" is the cause of the tripping. You should be using Toolbox's Trender to record SRV Position and Reference, GCV Position and Reference, IGV Position and Reference, and the Pressure Feedback from every P2 pressure transmitter. You also need to monitor L4 to see when it's being dropped out, and L4T to see when it's going to a logic "1", and all the logic signals which can make L4T go to a logic "1" to see which one is tripping the turbine.

None of the alarms appear to be the cause of the trip. Exactly what is tripping the unit? There should be an alarm describing the trip, even if it's 'Loss of Flame Trip'. What is the condition which is tripping the turbine: excessive P2 pressure spread for a period of time which exceeds the limit?

We just don't have enough information.

Have you looked at the Trip History information?
 
Thanks for your reply to this mail. Please note answers to your questions:

1. This is a TMR MK-VI system.
2. We have looked into the history, and I can send it to you. Please tell me your mail ID.

As our turbine is running since evening of June 22, 2008, and until now, I wanted to add more points that will clarify work done thus far, and please you can comment.

1. SRV and LVDT have been open and checked. Installed, and calibrated.

2. All instrumentation on the Hydraulic system has been checked for calibration, and it was good.

3. During the check for the Hydraulic system, we have found that one of the ½� lube oil tubing furls has come out by itself, and then later it was replaced with new tube furl. As we have explained in the original mail, that there is a suspicion about one element in the lube oil circuit that is causing this frequent GT tripping, and our MANT staff somehow satisfied that the cause of the problem was because of tubing fault.

4. In the afternoon of June 22, 2008, there is was an attempt to start the turbine but during initial start-up the electric drive motor has tripped on high temperature RTD while it was in the sequence of start-up. Later our people checked, and they learn that they found a loose connection with RTD, and hence, it was rectified.

Please note the motivation to contact this list was to ensure that if there are any concerns about what we have done, then other people may share their experience, with us to do further preventive steps, that will ensure of our turbine continuous and reliable operation.

Also, I wanted to point that during this troubleshooting, we have found some cables having two problems: lose connection at the terminal board, and grounding.

Regards
 
Thanks very much for the feedback! If everyone provided feedback, this list would be invaluable; as it is, it's still useful.

You still haven't told us the *EXACT* trip conditions, but I suspect, and you have basically confirmed, that you are experiencing multiple problems.

The SRV regulator is *NOT* a position loop; it's a pressure loop. It will put the SRV at whatever position is required to make the actual P2 pressure equal to the P2 pressure reference. Period. Loose connections (you also didn't say what circuits you found the loose connections in!) can be very problematic.

One of the best things anyone can do periodically is to go through every junction box on the unit and any marshalling cabinets and the Speedtronic turbine control panel, and check each and every connection for tightness. That *DOES NOT* mean to over-torque every single screw, but just to check to ensure there are no loose terminations. Those units run at approximately 5100 RPM, and the vibration is high at times. Also, immediately after every start-up I used to send the electrician with a black felt-tip marker and screwdriver to open every junction box, check every screw, and when finished put a mark on the JB cover to indicate it had been opened and the screws checked for tightness. *MANY* intermittent problems can be traced to loose wires, even bad crimps.

The loose compression fitting was a good catch, though it could have been caught by monitoring servo-valve output currents vs. positions.

Good news, nonetheless; continued success! Thanks for the information.
 
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