Our GE frame 9e gas turbine experienced auto shutdown from base load because unloading was not occuring at the time of sudden fall of gas pressure rather SRV opened 99 percent and took auto shutodwn command.

At 60 percent load SRV position got back to 40 percent. Then we paused the shutdown by giving a Start command. Now is there any adverse effect of pausing the shutdown. Please help me understand the situation

 

What Process Alarms were annunciated when the gas supply pressure was falling, and during the auto shutdown?

As for any consequences of the abort of the shutdown by issuing a START after supply pressure was restored--that's the exact proper response and action to take to abort (cancel) the auto shutdown. So, there are none for a typical control configuration. Unless the generator breaker opened in Reverse Power, a START used to abort an auto shutdown when gas pressure is restored is the best course of action, and will have no ill effects.

To provide any further assistance, we would need to know the Process Alarms which were annunciated during the event. There may also be some non-standard sequencing which we can't examine which was triggered by the fall in gas supply pressure. Generally, even for single fuel machines, a loss of gas supply pressure results in an excessive opening of the SRV as it tries to maintain the P2 pressure between the SRV and GCV. And, unless there's a run back or shutdown initiated on excessively low pressure the load will decrease simply due to the decreased fuel flow-rate. Allowed to fall low enough, flame will usually be extinguished, resulting in a 'Loss of Flame -Trip.'

Some machines seem to have some logic to go into automatic shutdown if pressure falls excessively, which should help protect against loss of flame, and may help to maintain load--but not always.

Without being able to see the configuration/programming in the turbine control system it may be impossible to say anything further. But, by providing the Process Alarms it may make further comment possible. Without more information, there's not much more can be said.

Hope this helps!

 

Thank you for your valuable comment.

Following process alarms came prior to auto shutdown sequence:
"SRV opened more than 90 percent risk of high exhaust temperature." Exhaust temperature was 560 degc.

Normally our GT unloads some MW when pressure falls down. At that day it did not unload rather initiated shutdown.

 

AHM,

<i>Based on the information provided</i> it's impossible to say what happened at that day versus other days.

The Process Alarm you listed seems to be a new one.... The GE Belfort Bunch (who have responsibility for the GE Frame 9E design and control and protection) infrequently and indiscriminately add new Process Alarms and functions simply because they can. The problem with the SRV going to more than 90% open is that if the gas fuel supply pressure increases very quickly then it may be respond fast enough to limit the exhaust overtemperature--especially if the unit is or was operating near Base Load when the decrease in gas fuel supply pressure occurs. 560 deg C (1040 deg F) is probably at or very near Base Load for the conditions at that day. And, it could be that during installation and/or commissioning that it was realized the site you work at would experience frequency gas fuel supply pressure disturbances and so some unique sequencing was added to try to protect the unit against tripping in case the human operators didn't respond quickly enough.

The exhaust overtemperature alarm is 25 deg F (14 deg C) above the Base Load exhaust temperature setpoint, and the exhaust overtemperature trip is 40 deg F ( deg C) above the Base Load exhaust temperature setpoint. So, this is likely the reason for the Process Alarm.

But, without being able to see the application code or sequencing running in the Speedtronic turbine control panel and some historical data for the event it's not possible to add anything further to what's already been said.