Hello,
I work at a power plant.
A few days ago, our turbine tripped and shut down. After the turbine stopped, I noticed that the Atomizing Air Booster Motor was still running.
I expected the motor to stop when the turbine was shut down, so I would like to understand the logic behind this operation.

• Is it normal for the Atomizing Air Booster Motor to continue running after a turbine trip?
• What signal or control logic keeps it running?
• Is it controlled by a timer, pressure switch, temperature signal, or another condition?

Thank you for your support.

 

@97133FHD,

Let me guess--the turbine is a GE-design Frame 9E manufactured in Belfort, France. OR, the original turbine control system of the Frame 9E was replaced by GE with a newer version. And, the machine was burning liquid fuel (heavy fuel or naphtha) at the time the trip occurred.

It's best to provide as much information as possible so that you get the quickest, most concise answers possible. If the machine has Dry Low NOx (DLN) combustors it's also best to tell us that in the beginning. The type of turbine control system is also helpful to know, as is the type(s) of fuel the machine burns and what type of fuel it was burning at the time of the trip. But making us guess just means you may get the answer you are looking for after some back-and-forth, or not.

Usually, the AA (Atomizing Air) Booster Compressor motor only runs when the machine is being started or shut down while burning liquid fuel. If the machine was burning heavy fuel oil (crude; bunker) it's possible the AA Booster Compressor was started to help try to clear the fuel nozzle of heavy fuel so that it won't carbonize due to the residual heat in the combustor.

Usually, the AA Booster Compressor is only used when starting on liquid fuel and is shut down when the machine reaches FSNL (Full Speed-No Load). Some divisions of GE have made changes to the typical logic which was successfully used for decades (for various and sundry reasons, and often without proper testing/verification of the new logic--GE Belfort is infamous for this practice).

So, without a lot more information it's difficult to impossible to say for certain what the logic is that controls the operation of the AA Booster Compressor (and its motor). Telling why the machine tripped and what the alarms were at the time of and shortly after the trip, and when the machine reached zero speed, could also be helpful in providing the information you are seeking.

 

Sorry for the confusion.


Our turbine is a GE Frame 7EA with a Mark VI control system.


The unit was operating on crude oil when the trip occurred.


The trip cause was reported as "Control System Fault."


After the trip occurred and the turbine shut down, I noticed that the AA Booster continued running while the turbine was offline and off. This is what surprised me and prompted my question.


When we restarted the unit and it reached FSNL, the AA Booster stopped.


I am trying to understand whether there is any logic that intentionally keeps the AA Booster Compressor running after a trip while the turbine off or if this behavior could indicate a control or logic issue.

 

Good day

At least we know that it is not a unit builded by GE Europ Belfort.

I don't have on my possession application code of Frame 7EA so can not support from here

Let's see if anybody else can support

 

@97133FHD,

To my knowledge and recollection, there is no logic that would keep the AA Booster Compressor running after a trip--unless it would be because the machine was burning crude at the time of the trip. Crude or heavy fuels can create some serious issues in the fuel nozzles if the machine trips while burning such fuels. The residual heat in the combustor assembly after a trip while running on crude or heavy fuel can and will cause the fuel to solidify (known as carbonization) in the fuel nozzle, and as the fuel heats and expands it can "leak" into the atomizing air passages. So, it's possible the system designers have tried incorporating the AA Booster Compressor for some help in cooling the internal fuel nozzle passages (specifically the AA passages) in an attempt to prevent carbonization.

In my experience with older machines, the pressure provided by the AA Booster Compressor is minimal, but there IS air flow so that will provide some cooling and perhaps prevent dripping and carbonization. Without being able to see the application code running in the Mark* VI it's impossible to say for certain.

Interesting alarm message.... I can't recall that one at this moment but it doesn't sound like what GE would classify as a Process Alarm and the "standard" is that no SINGLE Diagnostic Alarm can cause a machine to trip (it would require an rare simultaneous occurrence of Diagnostic Alarms to result in a turbine trip; yes, one Diagnostic Alarm--combined with several other pre-existing Diagnostic Alarms--could cause the machine to trip, but that one Diagnostic Alarm, by itself, should not result (by design) in a turbine trip, at least that's always been the GE-design heavy duty gas turbine controls philosophy).

It would be MOST helpful for many people reading this thread--now and in the future--if you would provide the list of alarms, Process Alarms AND Diagnostic Alarms, that were existing PRIOR to the trip and that occurred within a minute or so AFTER the trip. If the HMI uses the ToolboST Alarm Viewer feature, this information should be available (though sometimes "digging it out" can take some time). I would be most interested in what happened immediately prior to the trip, as well as shortly after the trip. AND, what actions were taken to resolve the CONTROL SYSTEM FAULT condition (was the control system re-started/rebooted? ???)

Anyway, again, without being able to see the application running in the Mark* VI at the time the trip occurred it's impossible to answer your specific question about whether or not there is application code/logic to keep the AA Booster Compressor running after a machine trip while burning crude oil after the machine reaches zero speed, and for how long. Me, given the suspected cause of the trip, it's entirely possible that something in the control system got mistakenly "hung" as a result of the trip (MANY things can be happening prior to and after a trip!), and while this would be highly unusual it's not outside the realm of possibility. As a technician/engineer I am always more interested in getting to the root cause of a machine trip, because it's quite often something very different from what was suspected or attributed to. Because of the way the Mark* turbine control system reports alarms and fails to block subsequent trip alarm messages AFTER a trip has already occurred) it can take some time to sort through an alarm list (in this case a Trip History Trend display from the trip!) to really see exactly what occurred. Most operators and even instrument technicians are not properly trained to do a proper analysis of a turbine trip event and mistakenly attribute the trip to an incorrect alarm in their efforts to restart the machine. MANY sites, operators, and Operations Managers are almost solely focused on re=-starting the machine as quickly as possible. If it starts, then everything is okay, right? (So the thinking goes anyway....)

Without more information, there's nothing more I can add. I'd love to help, but, more information would be necessary.