Turbine Compartment Ventilation


Thread Starter


we are having three number of frame 6B,30MW machines. each turbine compartment is having two no. of BT i.e. turbine compartment vent fans.<pre>
GT1 mark 6 - both fans running, temp is 120degc
GT2 mark 6 - s/b
GT3 mark 6e - with one fan running, temp is 110 degc
-with both fans running, temp is 85degC
above temperature is at fan suction</pre>
mark 6/6e gives turbine compartment temperature high alarm >95degC .
But PCRA (petroleum conservation and research association) suggested to run one only BT fan.

Are temp (>95deg C) are dangerous in long term? and how?
and what may be the reason for temperature differences in case both fans running in GT 1 and 3?

Sorry; I'm not familiar with "s/b", and I did use my preferred World Wide Web search engine to look it up. Standby; Should Be; Stolen Base; Seen By; etc.; nothing related to technical terms that I could find. I even tried Latin (since I've been remiss for not considering that before).

Anyway, without being able to see the application code running in the Mark VIs and the Mark VIe it's extremely difficult to say what should happen when the turbine compartment temperature is above the setpoint.

<b>AND,</b> it's not clear how the measurements were taken/recorded. Is there a T/C or RTD at the suction of the fans that is connected to the turbine control system(s)? Was an infrared, non-contact heat "gun" used to measure the temperature?

Is the calibration of the compartment temperature switches verified to be accurate?

And, lastly, the point of your post/question is not clear.

The PRCA, huh? (Thanks for explaining that acronym; it also stands for Professional Rodeo Cowboys Association.) I'm sure that PRCA was started in opposition to the API (American Petroleum Institute), which for many decades has had recommendations on similar things (in fact it wouldn't surprise me to learn the recommendations of the two organizations are extremely similar--only the names were changed to protect geopolitical differences). The designer of the heavy duty gas turbines recommends to run only one fan at a time under normal operating circumstances--that's the recommendation that counts. The fans are intended to be redundant, so that if one fails the other can be put into service (and, usually, there are (differential) pressure switches used to sense when the output of one fan is so low as to require the second fan to start). They are NOT intended to be operated simultaneously for long periods of time, only in "emergency" situations.

Usually, the insulation of the wire used in the turbine compartment is good for 90 deg C, so long term exposure to temperatures above 90 deg C can cause the insulation to be damaged or melt, which could lead to battery grounds as well as shorts which can cause trips.

If the turbine compartment temperature is above 120 deg C with both fans running, then something's amiss. There are leaks (either from the axial compressor discharge casing, or piping, or the combustion wrapper, or the turbine casing) or there is a problem with the fans (the direction of rotation is incorrect, or the louvers are not fully open, or the louvers at the base of the compartment aren't working correctly)--but something is amiss to cause those excessive temperatures. Which over time, aren't going to be good for the wiring in the compartment (of which there isn't usually very much, but does usually include IGV actuator wiring and IGV LVDT wiring, as well as fire detector wiring, and sometimes flame detector wiring).

Differences can be due to MANY things--measurement method being the most likely (physical sensor or non-contact, infrared heat gun; placement of any T/C or RTD which is being used to measure the temperature; etc.). Other reasons can be the locations of incoming air vents being different; the locations of leaks discharging hot air into the compartment can be different; differences in fan design; etc. I've seen MANY centrifugal fans which were running backwards--because the direction of rotation arrows on the fan housing had been painted over, and because GE and packagers of GE turbines often use reverse tangential fans. Reverse tangential fans have vanes that curve in the opposite (or reverse) direction of normal centrifugal fans, leading an inexperienced individual to believe the fan should be rotating opposite of what it should actually be rotating just by looking at the angle of the vanes. I've even seen two redundant fans rotating in opposite directions....

If a reverse tangential fan is rotating in the wrong direction it will move very little air, AND it will generally draw excessive current which will usually cause the TOL (Thermal OverLoad) relay of the motor starter to actuate and generate a Process Alarm. Usually, most technicians just crank up the variable TOL adjustment to try to get around this, instead of comparing the actual current (measured with a clamp-on ammeter) to the motor nameplate current, and if the actual is in excess of nameplate then trying to determine why the actual current is excessive--like the fan is rotating in the wrong direction.

If two redundant fans are both operating and rotating in the wrong direction, they will also be moving very little air.

Finally, most of these compartment vent fan arrangements use some kind of weighted damper on the output to prevent air from being drawn in through the other fan when only one fan is operating. It's quite common for these dampers to get rusted and damaged during maintenance outages and either stick open or closed, reducing fan efficiency. Depending on whether the compartment is pressurized by the fans or under a negative pressure from the fan suction, some arrangements use a latched, weighted damper mechanism which is to close when CO2 is discharged into the compartment--but are to be latched open at all other times (the latch is operated by CO2 pressure). It's VERY common for the latches to become unhooked or to be damaged, again reducing fan efficiency.

So, without being able to see the application code, or know how the compartment temperature is being measured, or how the redundant fans are arranged, or how cooler, outside ambient air is drawn into the compartment (or if it's forced into the compartment by the fans), or if the fans are rotating in the proper direction (one or both), or if there are leaks of the axial compressor or combustion wrapper or turbine casing into the compartment of one or two or three units, it's really impossible to say what may be causing the high compartment temperatures. (It's common to use a light rag on the end of a long stick to look for leaks in the turbine compartment. And, if you find a small leak coming from the bottom of the poro-stone filter for the compressor bleed valve solenoids, or from piping low-point drains--those are NORMAL; see the relative P&ID for the location of "Continuous Low-point Drains" and "-Orifices." They won't cause excessive compartment temperatures, and shouldn't be blocked or shut off or removed--they're supposed to be there. Again, review the relative P&IDs.)

Please let us know what you find!