Loss of ventilation


Thread Starter

sherif elzoghby

My GE 9001E tripped from baseload during i was changing the venilation fan although the alarm was

generator breaker tripped but the assumed action in this case is loss of ventilation and fast shut down not trip

can any one illustrate this trip ?

thank you
What's to illustrate ? Turbine compartment trip is L86BT and gas module is L86VL. What vintage is your machine ??

There are normally 2 fans, lead and lag. Failure of the first fan is an alarm, and starts the seconds. Failure of both is a turbine trip.

There is a bunch of stuff to indicate a failure. The damper ventilation limit switches, feedback from the MCC indicating an overload trip, and 2 out of 3 airflow sensors located in the ventilation duct. We've had a lot of trouble getting our airflow switches reliable. Also the alarms are latching ie. a master reset has to be issued before a faulty fan is reenabled.

Our site also has a SIL panel which has additional monitoring of the turbine enclosure. This protection loop is enable once gas fuel flow is detected via a coriolis meter.

sherif elzoghby

according to that when the loss of ventilation alarm is supposed to appear if the turbine will trip. knowing that loss of ventilation gives me fast shutdown status according to GE texts and also it happened with me when i stopped the two turbine fans at turning gear mode and when there was loss of AC.

can you tell me what is the difference?
sherif elzoghby,

How old are the units?

Do they have DLN combustors or conventional combustors?

Is there a hazardous gas detection system in the turbine ventilation duct? Was it working? Was it in alarm prior to the attempted change-over?

You say you were changing the ventilation fan; how? By changing the selection of LEAD fan from the HMI, or by manually switching over fans from the fan motor starters? If you were using the LEAD/LAG selection on the HMI it's hard to understand why the second ventilation didn't start, and if it didn't start why the other ventilation fan didn't re-start?

If turbine compartment ventilation is so important to these units, it would seem if one was using the LEAD/LAG selection from the HMI the application code in the Speedtronic would start the second fan before shutting down the currently-running fan--just to avoid any possibility of a loss of ventilation if the second fan did not start. I've never encountered such sequencing; in fact, I've never encountered sequencing that tripped the turbine on a loss of compartment ventilation--except for F-class turbines with hazardous gas detectors. And then only in a crazily-regulated part of the world where they were terrified of natural gas (and in fairness it was NOT odorized, so some of the fear was reasonable, but the stories about other regulations would make a sane person cry).

Do you have a printout of the alarms just prior to the event and for a 1-2 minutes after the trip?

What alarms were annunciated and active prior to the event? Why was the ventilation fan being switched--because of a high temperature alarm, or a hazardous gas detector alarm?

What does GE say about the occurrence?

It has been said MANY times before on control.com: The information in GE manuals is almost always generic and the <b>ONLY</b> description of the actual operation of a turbine and auxiliaries is what's running in the Speedtronic turbine control panel for THAT PARTICULAR TURBINE. What anyone reads in a GE manual is to be taken as "intent" and not the actual, factual description of what's running in the Speedtronic turbine control panel. You can read every sentence and paragraph, and it can ALL BE WRONG--completely different from what's actually running in the Speedtronic turbine control panel.

If you want to know how your turbine and auxiliaries operate, what trips the turbine, what causes a fast shutdown, etc., the only "written" description of how your turbine and auxiliaries operate is to review the sequencing or application code running in the Speedtronic panel for that particular turbine.

And, a thorough, comprehensive review of the Alarm Printout before and after the event will probably reveal a LOT about what really happened as opposed to what "appears" to have happened. There is also usually some kind of Trip History Display that could be helpful in sorting out what really happened and when--and what tripped the turbine. A generator breaker open on reverse power is not a trip--it's more like a normal shutdown.

So, without being able to see a chronological list of alarms before and after the actual event, and without being able to see the sequencing/application code running in the Speedtronic turbine control panel there's not much more which can really be said about this request. There just isn't enough information, including the age of the units, the type of combustors, the type of ventilation system (including hazardous gas detectors and what state they were in when the event started), the way the ventilation fans were being switched (via the HMI LEAD/LAG selection, or manually via the fan motor starters).

But to be able to say with any degree of certainty, it would be necessary to review the sequencing/application code running in the Speedtronic. And, the chronological list of alarms prior to and after the event.

sherif elzofghby

For more clarification. i want to know the difference between two cases

1- loss of AC source--all the motors will stop including ventilation fans but the unit will shutdown and can be reloaded

2- ventilation fans only lost-- the unit will trip directly
thank you
sherif elzoghby,

As has been said many times on control.com: It's virtually impossible to say for certain precisely how your machine would respond to specific conditions without being able to see the application code running in the Speedtronic panel at your site.

Further, if the turbine was packaged by GE in Belfort, France, it's even more difficult to say what might--or might not--have been done in the application code. They are famous (some would say notorious) for changing long-standing operating practices and philosophies, simply because they can and in their sole estimation it is warranted and acceptable.

If your site is subject to technical regulations and standards for hazardous gas detection and protection--or the site is required by the owner to implement hazardous gas detection and protection--then it's likely to presume that some coordination with the appropriate agency/person was done in the design and implementation of the application code for the protection of personnel and equipment.

I would estimate, based on 309Eguy's input last year, that hazardous gas detection is at the root of your dilemma. Not simply the loss of a fan or air flow, but the loss of evacuation or pressurization of a compartment where hazardous gas may be present causing a possible explosive atmosphere which may maim or kill personnel as well as damaging equipment.

It's likely to assume that in the event of loss of ventilation a runback (fast unload to some low load, or even FSNL) or even a shutdown (normal unloading to breaker opening, and then a normal fired shutdown to Cooldown) would occur--just to protect the turbine and devices and instruments in the turbine compartment. But that's just for equipment protection--not taking into account the possibility of hazardous gases in the turbine compartment.

So many regions of the world are now implementing very strict regulations and codes and standards for detection of hazardous gas--primarily for the protection of personnel working in the area. If there's no method to ensure a movement of air in the compartment to prevent the collection of hazardous gas in some area then it might likely be required that the turbine be tripped.

Some implementation of hazardous gas detectors use sensors in air ducts of the ventilation fans or outlets to sense hazardous gas. If there's no vent fan to provide movement of air (and possibly hazardous gas) past the sensor, then it might be a requirement to trip the turbine.

Some locales use gas fuel that is not odorized--and this makes hazardous gas detection and protection even more important, because personnel working in the area can't smell the gas fuel and evacuate the area for safety.

There are all kinds of possibilities--but the <b>ONLY</b> way to know what's going to happen at your site in any (every) case is to review the application running in the Speedtronic panel at your site.

It's also been said many times before on control.com: There is a difference between a shutdown (STOP) and a trip. A trip is what happens when some condition is detected that causes the fuel stop valves to be shut very quickly. The generator breaker will usually trip on reverse power as flame is lost and speed begins to decrease. If the SOE for generator breaker opening (tripping--opening a generator breaker is (unfortunately) commonly called tripping)--or there is a Process Alarm to indicate that the generator breaker opened (the test is usually (unfortunately) 'Generator Breaker Tripped) then you might see that in the Alarm Log.

But <b>EVERY</b> condition that results in a trip MUST (should) have a Process Alarm. Sometimes reading or interpreting the Alarm Log to determine what precisely tripped the turbine is difficult, but not impossible. If you're looking at an actual printout of alarms and events, the trip will be the alarm nearest the bottom of the page that says "trip"--not the "trip" alarm at the top of the page. It's extremely unfortunate that GE still has not blocked any trips which might be detected AFTER the turbine has been tripped from alarming--but they haven't, and that's what makes reading Alarm Printouts difficult. But it's NOT impossible--and someone (or two or three) at the site should be either well versed in reading Alarm Logs, or should be charged with becoming well versed in reading Alarm Logs.

A shutdown is defined to be a condition that results in a reduction in load (may be fast, may be at the normal automatic loading/unloading rate) until the generator breaker opens and then a normal fired shutdown (deceleration) to Cooldown. A shutdown can be initiated by an operator (initiating a STOP) or it can be caused by some condition the packager of the turbine deemed to be worthy of stopping the turbine--but not so dangerous as to require a trip. Trips are hard on hot gas path parts--they cause a high thermal stress on the parts which decreases parts life, sometimes greatly. So, GE is trying to do as much as they can to reduce the number of trips, and are implementing more shutdowns to protect against excessive thermal stress on the hot gas path parts.

Every "automatic" shutdown (those caused by the detection of some potentially harmful event) is also SUPPOSED to have it's own alarm--and that alarm, on a printed Alarm Log, would also be the one closest to the bottom of the page (before the 'Generator Breaker Tripped' alarm). It's entirely possible that a fast shutdown was initiated, and if the machine is a DLN machine that it didn't successfully transition combustion modes while unloading and tripped on loss of flame or some other problem.

From your posts, it's not clear--and it seems you can't determine from the Alarm Logs (printed or electronic) precisely what happened.

But, without being able to see the application code running in the Speedtronic panel at your site--and without being able to see the Alarm Log from the event--it's impossible to say what might happen in this or that scenario, and what did happen when you were changing fans. (Which, by the way, you never did clarify for us how you were "accomplishing" that little task.)