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GE Gas Turbine accessory and load gear compartments temperature running high
GT's Turbine accessory and load gear compartments temperature are running very high close to trip value of 450F.
By Abdur Rehman on 12 June, 2013 - 3:27 pm

we have GE frame5 Model R gas turbine at our plant. We use to run this GT by keeping its turbine, accessory, and load gear compartment doors open. A month ago we closed the doors and afterwards operator observed that compartment temperature had been raised near to trip value of 450F. so,we again opened the door to normalize the temperature in the compartments. Kindly suggest is it in GE design to operate this GT by keeping doors closed or open?

Secondly we are planning to install thermocouples with in the turbine and accessory compartments for online monitoring of temperature on Mark V HMI. this is some thing which is not in the design of This GT. is it feasible? if yes, then what should be the location of thermocouples in compartments? and at what temperature alarm must be configured on these thermocouples?

Also please share the design flow and pressure of pressurizing fan (ventilation fan) which it maintains in turbine and load gear compartments for this model of GE gas turbine. In our case ventilation fan is not working properly.

Abdur Rehman,

Running with compartment doors open means if a real fire is detected and extinguishing agent is discharged, the extinguishing agent will not be effective because it will not remain in the compartment.

Also, air will be allowed to enter the compartment through the open doors, and since air contains oxygen which is required for combustion the fire will not be starved for oxygen as it should be if the compartment doors are closed and the ventilation louvers (gravity-operated and/or latched) are working correctly.

If you have a Frame 5 heavy duty gas turbine packaged by GE (not one of its licensed turbine packagers) then you should be able to find a P&ID called 'Heating & Vent Flow' or something similar. If the unit is older, many of these diagrams listed heat loads and sometimes air flows, though not always.

As for fan flow ratings, every GE-design heavy duty gas turbine package was different, and depending on the ambient and customer requirements so were the ventilation fans and schemes.

Most of the time when I troubleshoot high compartment temperatures I find the ventilation louvers are not working properly, especially any latched dampers/louvers. The latches are operated by fire extinguishing agent pressure (when discharged) and when unlatched by fire extinguishing agent pressure large weights close the louvers/dampers with gravity. Most sites are completely unaware of these latches and never check to make sure the dampers/latches are properly opened/latched after maintenance outages or fire extinguishing agent discharge.

Also, many times I find ventilation fans running backwards. GE, and some of its packagers, used quite a number of reverse tangential centrifugal fans which actually turn in the opposite direction from what one would expect (when running in the proper direction and producing proper air flow) by looking at the angle of the fan blades. When running in the opposite direction, they also draw excessive current while producing much lower air flows--which usually causes technicians/electricans to change thermal overload relays to higher ratings to keep the motor starters from tripping. Which usually leads to premature failures of the vent fan motors.

So, make sure the compartment ventilation dampers/louvers are working properly, are latched open (if so equipped), and that vent fans are running in the proper direction. One way to be sure vent fans are running in the proper direction and producing near rated air flow is to use a clamp-on ammeter to check the current being drawn by the motor. If the measured current is at or near the motor nameplate rating then the fan is producing at or near rated air flow. If the measured current is less than or much less than rated, then the fan is not producing rated air flow. If the measured current is more or much more than rated, then it's probably not producing rated air flow--and just exchanging any two of the motor's three phase leads to reverse direction and re-checking current and air flow may help solve the problem.

Finally, if you are still having problems, then it would be wise to get someone knowledgeable to site to help with the problem. Because running with compartment doors open is asking for BIG trouble if a real fire ever does occur!

Please write back to let us know how you fare in resolving your problems.

Installing T/Cs in compartments isn't going to do a darn thing to help reduce compartment air temperatures. Nothing. If fact, it can be very misleading if the T/Cs are not placed in strategic locations (which will vary with compartment configuration). (Which leads to question: How do you know what the compartment temperature(s) is(are) without some kind of sensing device--unless the high-high compartment temp switches are activating, in which case, you are really "playing with fire" by blocking the trip!)

Lastly, exhaust leaks are another common cause of high load compartment temperatures.

Best of luck!

By Abdur Rehman on 14 June, 2013 - 5:16 pm

firstly,thanks for your detail reply.

1-there is no fire extinguishing mechanism in our GT which can be actuated automatically on fire. This is something not incorporated in the GE frame5 GT we have.

2-No P&ID is available for ventilation system of this GT.

3-You right in saying that ventilation fan is not working properly and we are also suspecting this. Fan and dampers checkup is on its way.

4-We conducted the thermovision monitoring of our GT. Temperature around exhaust plenum in load gear compartment is about 650F. This gives an indication of leakage there. We are planning to address this as well.

5-We have 4 thermal fire detectors installed in Turbine Compartment having trip at 450F. One thermal fire detector in load gear compartment having trip at 450F. Two thermal fire detectors in accessory compartment and one in generator compartment having trip at 325F respectively.

6-After addressing the all suspected causes of temperature rise,we will close Gt doors and to have online monitoring of running temperatures, we are planning to install four thermocouples. Two in each turbine and load gear compartments near already installed fire detectors. Could you please suggest that at which temperature alarm should be configured (2oo2 logic) on these thermocouples,to warn the operating staff about the rising temperature well before the Tripping values (mentioned above).

7-Could you share the specification of these thermocouples. If you have any in your record.

8-Could you please also suggest the normal pressure in the GE frame5 Model R gas turbine compartments if we have pressurizing fan operating normally with Gt doors closed.

> 2-No P&ID is available for ventilation system of this GT.

Note: GE calls their gas turbine P&ID's "Piping Schematics"
If you have the Device Summary (also known as the 0414 drawing), it should list all the Piping Schematics.

By Abdur Rehman on 5 August, 2013 - 12:42 am

please provide more help in this regard. The issue of high temperature is still persisting.

Dear CSA

we are planning to have thermocouples ionstalled near already installed fire detectors, and only alarm is to be configured on these thermocouples. please suggest if it is going to work for online monitoring of temperature?

1 out of 1 members thought this post was helpful...

Abdur Rehman,

> We are planning to have thermocouples installed near already installed fire
> detectors, and only alarm is to be configured on these thermocouples.
> please suggest if it is going to work for online monitoring of temperature?

The Mark V can accept most all types of T/Cs; check the Mark V Maintenance Manual, GEH-6195, for more information.

As for the style of T/C, try www.omega.com. They have excellent publications for just about every type of sensor, detailing how they work, installation methods, and examples.

However, it's not clear how installing temperature sensors near the fire detectors is going to solve the problem of insufficient cooling. It may prevent nuisance trips by allowing operators to open the doors, or lower load, but does that solve the root problem: insufficient cooling?

You have NOT answered any of the questions about damper operation, or cooling fan rotation. You have not provided current measurements of the existing cooling fan motor(s) versus the motor nameplate rating. Current is directly proportional to the work done by the motor, and if the current drawn by a motor is not nearly equal to the motor rating then it's a safe bet the motor isn't working very hard. It's not very common to use a more powerful (and expensive) motor than the application (in this case, a fan) requires. The fan will only draw as much current as it requires to move the air. It's customary to use motors rated to provide nearly the same amount of power as the device it is driving is required.

Simply measuring the temperature in the area of the fire detectors isn't going to help resolve the problem of insufficient cooling. If the unit was working fine for some time, but then the doors were opened because of high temperature, and now someone (usually someone in management) wants to simply close the doors but the high temperature problem is not resolved, wasting money and time (which is also money!) installing T/Cs isn't going to solve the root cause of the problem: insufficient cooling.

So, what's changed since the time the unit was run with the doors closed, to the time it was started being run with the doors open?

Help us to help you. We can't provide more help without answers to the questions that have already been asked. Again, help us to help you by providing the requested information. We aren't there to see your specific installation. It's not common for turbines to be run without automatic fire extinguishing systems, so this is unusual--at least in my experience.

All GE Frame 5s suck (draw air into the compressor), squeeze (compress the air), burn (combust fuel to make high temperature, high pressure gases to input to the turbine section), and blow (exhaust). The physics are the same, but the actual configuration of the package the turbine is provided in and the auxiliaries it's provided can--and do--vary. I've been to multi-unit sites, where the turbines (same Frame size) were purchased and installed several years apart, and while they are similarly rated (power output), the packages (enclosures) and auxiliaries can be very, very different. They all start with the "push of a button" (or the click of a mouse these days), and they all burn fuel and exhaust high temperature gases, but the similarities end there many times. Even for the same series of turbines.

Wish we could be more help. But without answers, just suggesting things is a waste of everyone's time. If we suggest something you've already done--but you didn't tell us until after we suggest it--is that a good use of anyone's time?

We feel your frustration, but there's only so much we can do without your assistance.

By Abdur Rehman on 6 August, 2013 - 11:29 pm

Dear CSA ....

I am working on this issue particularly on the pressurizing fan. Will definitely reply you with details of it within few days.

T/C installation will be just to monitor the temp after sorting out the true cause of temp rise and solving it.

thanks for sharing the info.

Abdur Rehman,

Thanks for the feedback.

As a bit of added information, every GE-design heavy duty gas turbine I have EVER worked on had either positive or negative pressures in the compartments when the ventilation fans and dampers and louvers were working properly.

If a fan is pressurizing a compartment, when the doors are closed and some walks up to the door and opens it it will "fly" open (often scaring the person opening the door if they are not expecting it!). And, if the fan is taking a suction on the compartment if someone attempts to open a compartment door it will take a great deal of effort to open.

These both assume that either the air being pushed into the compartment by a pressurizing fan can get out through the compartment's exit dampers and louvers (quite often they get stuck), or the air being drawn out of the compartment can be "replenished" by air being drawn into the compartment through the entrance dampers and louvers. In either case, air needs to get out of the compartment (in the case of pressurization by the fan) or into the compartment (in the case of the fan drawing a suction on the compartment) for cooling to work properly.

If the exit dampers or louvers are not working properly, the positive pressure will be higher than it should be and the doors will really "fly" open when unlatched. If the entrance dampers or louvers are not working properly the negative pressure will be higher than it should be and it will take a great deal of force to open the compartment doors.

Some fans have dampers or louvers on the suction side of the fan, and some on the discharge side of the fan, which must also be working properly.

In essence, what you need to solve is: Why is the air flowing into (or out of) the compartment not sufficient to cool the compartment properly?

If you resolve the air flow problem (fan; dampers; louvers) you can use an infrared heat gun (always aimed at the same location/device in the compartment) to measure changes in temperature. You could do that whilst troubleshooting, also.

Of course, this requires a human to get up out of his chair, and go out of the air-conditioned control room or office and take a measurement; not as easy as an operator pointing to a value on a display....

We are looking forward to hearing the resolution(s)!

Please kindly tell me the right direction of rotation of 88vg load gear compartment vent fan motors. should it be blowing or sucking?

Thanks

WillyBlackson,

If you're working on GE-design heavy duty gas turbines, the 'Heating & Ventilating Flow Diagram'--one of the group of Schematic Piping Diagrams, or P&IDs (Piping & Instrumentation Diagrams)--will show whether fans are used to pressurize or evacuate compartments with very simple arrows showing the direction of air flow into, through and out of the compartment.

You should know that it's quite common for some compartment to be pressurized and others to be under a slight vacuum--on the SAME turbine. The common thought is that all compartment should be under pressure by the vent fan, or all compartment should be under a slight vacuum by the vent fan--but, unfortunately, that's not always the case, and frequently compartments of the same unit are under pressure and vacuum when proper ventilation is being provided.

But, the 'Heating and Ventilation Flow Diagram' provided with every GE-design heavy duty gas turbine package will definitely show air flows through the compartment. There is usually a tab in the Operation, Maintenance and Parts manuals provided with GE-design heavy duty gas turbines with all of the P&IDs (Piping Schematics, or Schematic Piping Diagrams as GE calls them), and the 'Heating & Ventilation Flow Diagram' will be included with them. Or, some manuals have individual tabs/sections with descriptions of every system, and you should be able to locate the 'Heating & Ventilation' tab/section and find information there.

One thing to know about some of the vent fans provided with many GE-design heavy duty gas turbines is that they frequently supply what are called 'reverse-tangential' centrifugal fans. This means that the fans rotate OPPOSITE to the direction one would generally think a centrifugal blower (fan) would rotate based on the angle of the fan blades. Reverse-tangential fans can move more air than their "non-reverse" counterparts for the same energy input (from the AC motor driving the fan).

Reverse-tangential fans, if operated in the wrong direction of rotation, will draw excessive current--over and above the AC motor nameplate. And, they will also move less air--though it will still be in the same direction!

Unfortunately, the direction of rotation arrow the vent fan manufacturer paints on the fan housing before they ship the fan to the turbine packager usually gets painted over either by the packager or by the owner. So, the question often comes up--which direction is correct? And, unfortunately, because GE-design turbine packagers were prone to using reverse-tangential design fans the question is not easily answered.

So, the "easy" way to determine if the fan is rotating in the proper direction is to measure the current drawn by the motor and compare it to the motor nameplate rating. If the current is equal to or slightly less than the motor nameplate rating (presuming all the dampers and doors are in their proper operating positions!!!) then the motor/fan is likely rotating in the proper direction. If the current is more than the motor nameplate rating, then the motor is likely rotating in the wrong direction.

Hope this helps!

By Leentje Adams on 16 April, 2018 - 12:19 pm

In general, are the customers whose load gear compartments are under vacuum having the same issue(s) and those under pressure?

>You should know that it's quite common for some compartment
>to be pressurized and others to be under a slight vacuum--on
>the SAME turbine. The common thought is that all compartment
>should be under pressure by the vent fan, or all compartment
>should be under a slight vacuum by the vent fan--but,
>unfortunately, that's not always the case, and frequently
>compartments of the same unit are under pressure and vacuum
>when proper ventilation is being provided.

In general, if there is poor airflow and/or hot air leaks, then yes. The direction of airflow (into or out of the vent fans) doesn't matter.