Good day. My name is Alexander Aka, am a controls and instrumentation engineer in Nigeria, Olorunsogo power plant we have four frame 9E GE gas turbines, one of our gt's gt-12 has been tripping without any alarm, when gas leak test complete sequence is on and after purge time of 3-5minutes @ 730rpm/24% and when the unit starts ramping down to firing threshold it trips @640rpm 20% speed, and no alarm of the trip, but as the unit is coasting down the srv opens again and close back with the alarm- shutdown gas leak test complete- l3gltsdtc_al.

Please i need some advice, thanks.

 

Mr. Alexander,

This is very strange; very strange, indeed. Usually, when I've seen something like this happen it's because something in the Start Permissive string drops out unexpectedly--and without an alarm--during the start sequence. Sometimes, it happens early in the Start sequence and there is an alarm, but the operator ignores the alarm.

Also, sometimes something external to the Speedtronic turbine control panel initiates a STOP during the Start sequence (which is NOT a trip and would not be alarmed...!) and aborts the Start sequence.

It's probably more likely that something is causing L94X and/or L94T to pick up, which is dropping out L4. You'll need to use whatever data gathering method or trending capability the version of Speedtronic turbine control panel you have to monitor L4, L4T, and L94T and L94X to see what's picking up to drop out L4 and causing this problem. Then you're going to have to continue to work backwards to find the real culprit (a signal from the DCS; or some other piece of equipment in the plant to initiate a STOP; or some logic which is inadvertently picking up to initiate a normal shutdown (STOP) which is not alarmed (it should be--but for some reason it's not alarmed); something like this.)

Please write back to let us know how you fare!

 

Is this a speedtronic system?

 

>Is this a speedtronic system?

Eh! Yes

 

I suspected just as you said. I already have a trend on it but will add more signals to get more troubleshooting insight about it. I will get back to you. Am now trying to check from the DCS too. The turbine control is GE MarkVIe control system.

Thanks

 

> Is this a speedtronic system?

The turbine control is GE MARK VIe control system.

 

Hmm.... Interesting... as I understand it, the GT trips during the initial ramp down from crank speed [for purging] to firing speed, even before firing speed is reached right? I think it would be useful if you tried 2 things:-

1] Just cranking, without force closing torque converter solenoid drain valve

2] Cranking after force closing torque converter solenoid drain valve.

 

That program to see the alarms you use. I use the Workstation ST Alarm Viewer is more accurate than the Historian or CIMPLICITY HMI. Following the events before the trip can guide what the problem is.

 

Thanks guys

i have resolved the problem, it was tripping on L94TC, which was sending a shut down to the sequence L94T and L94X.

 

Mr. Alexander,

Thanks for the feedback!

What, pray tell, is L94TC, and why was it causing a shutdown?

How did you resolve the "false" L94TC shutdown?

 

And, was there truly no Process Alarm alerting the operator of the issue?

If there was no Process Alarm, was there a Diagnostic Alarm (or three) warning of a failed input it Voting Mismatch?

 

we have increased our k94tc from 5 seconds to 8 seconds. It makes the time when shutdown or on turning gear but takes longer when at cranking speed.