BT Fan Stopped on Cooldown Timer Complete


Thread Starter

vimal gupta

Dear Sir,

In our Frame-V machine, Turbine vent fan stop logic in auto taken when cooldown timer completed (24 Hrs) after stop the machine.

There is no logic to start the stand by fan in auto on compartment temp high.
There is no logic to stop the running fan when compartment temp low.
There is no l26BT1/2 switch provided in field, new block configured from attc1 & attc2 but it is not incorporated in turbine vent fan Logic.

Kindly guide us to correct logic for BT1/2 & other fans.


vimal gupta,

Here you did not mention about your GT model/frame specification..

By the way, I can give you general idea according to my site (9FA.03 with Mark Vie) specification.

88BT-1/2 (For GAS TURBINE compartment Cooling) redundant motors run logic "L4BTRUN" should be true if any one of following logic is true:

1. During start up if flame is detected and this logic will remain true till "L28FDZ" is true.

2. While GT is running , at that time if ATTC (Turbine compt temp)> 46 degree celcius.

3."L4BTRUN" should remain true up to ATTC (Turbine compt temp)> 177 degree celcius.

4. If Master protective circuit is true (L4=True).

5. If turbine compartment any hazardous gas detector detects HIGH signal, "L4BTRUN" will remain true. OR if, gas valve room off base hazardous gas detector detects HIGH signal.

But of course if, Fire Detector Signal "L45FTX" is true, you can not run 88BT-1/2 as "L4BTRUN" will be FALSE.
vimal gupta,

First, how old is the Frame <b>5</b> machine?

The reason I ask is because many newer machines do not run the BT compartment vent fan(s) during cooldown--because running the fan during cooldown causes the axial compressor casing to cool much faster than the axial compressor rotor and is known to cause rubs which reduce clearances between the rotating blades and the casing, and the stationary blades and the rotor. Many newer machines stop the turbine/accessory compartment vent fans when flame is extinguished in the combustors.

Second, has something changed recently? Is the fan sequencing different from what it was before? Why is it felt the fan sequencing is incorrect?

Third, is it normal for the turbine compartment temperature to go into alarm during cooldown with the BT fan running? Or, is it normal for the turbine compartment temperature to go into alarm after the Cooldown timer expires and the BT fan shuts down? Because that's not really normal in my experience.

Fourth, you mention lead/lag BT vent fan logic. Does the unit have redundant BT vent fans, mounted on the roof of either the turbine or accessory compartments, or the tube-axial vent fan(s) under the inlet plenum between the accessory and turbine compartments?

Fifth, what turbine control system does this unit use?

There have been several versions of vent fan logic for various compartment ventilation schemes, some of which "pressurize" compartments and some of which "draw" on compartments. The tube-axial vent fan scheme drew air into and through the accessory compartment and discharged that air into the turbine compartment and out of dampered openings--cooling both the accessory and turbine compartments. Some turbine compartment roof-mounted vent fans drew air into the turbine compartment through dampers near the bottom of the compartment and discharged to atmosphere out of the fan exit. In these units, there were usually separate accessory compartment vent fans to cool that compartment.

Load compartment ventilation was also done differently over the years.

I'm going to guess the control system is either a Mark VI or a Mark VIe, but it would be helpful if you could confirm that for us. And, I think 'attc1' and 'attc2' are thermocouples mounted in the turbine compartment. And, I don't understand about the missing lead/lag selection " the field...." It would seem if there are redundant turbine compartment temperature sensors (thermocouples) they could be used to cycle the lead turbine compartment vent fan when the turbine compartment temperature goes into alarm, shutting them down when the temperature drops approximately 25 deg C, or something like that.

BUT, I caution you--quite often the way the T/Cs are mounted in the turbine compartment is not always the best, and so they measure metal temperature rather than air temperature. Or, they are "shielded" from normal air circulation when the vent fan is not running. Or, they are in the vent fan suction (inlet) and are abnormally cooled when the vent fan is running.

AND, not cooling the turbine compartment too quickly when on Cooldown is also advisable.

As long as the unit is not in warranty from the packager/OEM, or under some type of Long Term Service agreement with some provider, you are free to modify sequencing as you see fit--as long as you're willing to accept the consequences of any changes. Well thought-out and carefully planned modifications are totally fine to make unit operation more reliable. But, time should be taken to consider as many (all, if possible) ramifications when making changes.

If you can provide more information, we can provide more help. But, based on the information provided, this is about all we can provide.
Thanks for information.
1) Machine is commissioned in 2012 by BHEL and control system is mark-Vie.

2) Since commissioning, BT-1/2 stops after cool down completion. We have not changed anything in logic or in field. I feel, BT fan purpose is cool down the turbine compartment temp and when it reaches some set point; BT fan has to stop.

3) Accessory compartment fan BA Fan stops on when wheel space temp water wash permissive L69TWW reaches 58 DEGC.

4) No alarm is appearing during cool down cycle on BT fan running.

5) No alarm is appearing after cool down completion on BT Fan stops.

6) Machine have 2 Vent fan in each compartment, Only one fan is running at a time. Other will be in standby.

7) Pls note that machine has low pressure switch compartment mounted on roof of compartments. Each compartment has 2 No switches. Tag: 63AT/1/2/3/4/5/6

8) Mark-Vie control system used for this machine.

9) I am also not sure about ATTC1& ATTC2 thermocouple measures compartment temp or sheath temp.

10) Please also tell me how to attache any logic into this forum. I am unable to draw or attach any logic diagram to post it.

Thank You.

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