Hi guys,

Our machine make is GE Frame 9E. We have two 3-phase vent fan (88BT-1 & 88BT-2 and one 1-phase vent fan (88BT-3) for the turbine compartment. As far as i know, both 88BT-1 and 88BT2 start running (depending which is leading and lagging) when the turbine speed is above 14HY (8.4% ~ 252rpm)and stop when the setting of temperature switch 26BT-2 is achieved (35 degrees celcius). 26BT-1 will cause the "Turbine compartment temperature high" alarm to be annunciated whenever the temperature reaches 149 degrees celcius.

I would like to ask why do we need 88BT-3? Load compartment vent fans only come in pair, why do we need the 88BT-3?

 

Hi, RY,

Turbine compartment vent fans DO NOT always come in pairs. Redundant fans are a purchased option, unless the turbine is located inside a building in which case most turbine compartments have redundant vent fans.

It's extremely interesting that you noted the operating characteristics of 88BT-1 and 88BT-2, but NOT 88BT-3.... It's pretty likely there is some sequencing/logic for the control of 88BT-3, and that could provide at least part of the answer to your question.

The majority of the answer to your question about 88BT-3 can be found on the Heating & Ventilation P&ID. Locate the fan on the drawing and note the direction of air flow through the fan and which area it is pressurizing or drawing air through; then, in conjunction with the sequencing/logic in the Speedtronic you can understand when it is to be running, and understand what it's function is intended to be.

Single-phase vent fans have been used to provide a small constant circulation in turbine compartments when the turbine is shut down. This is usually done when local regulations require some constant ventilation of turbines which run on natural gas fuel. (Not that this is required only for natural gas fuel; vapors from liquid fuel leaks puddled in the bottom of turbine compartments after the turbine is tripped or shut down are just as explosive as gas fuel leaks. It's just that regulators in some parts of the world are absolutely terrified of natural gas, because they have only had experience with liquid fuels.)

So, have a look at your Heating and Ventilation P&ID and the sequencing/logic for control of 88BT-3 and you likely answer your own question!

Hope this helps!

 

Hi RY,

enclosure philosophy require several things .

enclosure temperature and enclosure pressure also gas methane concentration inside enclosure.

1 of 2 fan is running to maintain enclosure under pressure and remove heat from gas turbine enclosure.

in case you lost one fan and your enclosure pressure drop a emergency fan start to establish pressure.mean time if enclosure temperature reach alarm threshold a signal logic command start emergency to cool enclosure.

last things loss of power of plant a 88BT3 emergency fan start automatically by lost of power from controller for cooling time of gas turbine enclosure post shutdown.

bests regards
from markvi