L86BTX- LOSS OF TURBINE COMPARTMENT VENT FAN TRIP

CHECKS WERE MADE ON THE 88BT, MOTOR ROTATION OKAY. GE FRAME 9E UNIT WAS STARTED, UP, SPEED RAMED TILL FULL SPEED NO LOAD, NO ISSUE. BUT DURING SYNCHRONIZATION, UNIT ENTERED FIRED SHUTDOWN AND THE GENERATOR BREAKER TRIPPED WITH THE FOLLOWING STANDING ALARMS; TURB COMPT COOLING FAN CHANGE OVER AND LOSS OF TURBINE COMPT COOLING FAN. PLEASE ANY SUGGESTIONS AS TO WHAT COULD BE THE ISSUE?
 
It sounds like the unit has redundant turbine compartment cooling fans (hence, the change-over alarm) and because they are very important for helping to remove combustible gases from the turbine compartment the Mark* was programmed to shut the unit down if there is not one turbine compartment ventilation fan running.

SOME (but not all) turbine compartment vent fans have dampers which are supposed to be latched open and gravity will close them when there is a fire and fire extinguishing agent (CO2) is discharged. Quite often, these damper latches will work themselves loose and allow the dampers to close, which will prevent proper ventilation of the turbine compartment. That's one thing to check.

Often, the turbine compartment vent fans are reverse tangential centrifugal fans--meaning they rotate in the opposite direction one would suspect they would rotate based on the angle of the vent fan blades. When this happens, too little air is moved and, usually, the vent fan motor trips on excessive current (thermal overload relay) because the motor draws excessive current when spinning in the reverse direction. DO NOT trust a direction of rotation arrow on the motor housing--there was a direction of rotation arrow painted on the fan housing by the manufacturer, and that usually gets painted over during construction. The type of fan blade determines the direction of rotation. (It's very common for the rotation to get "confused" after the motor(s) has(have) been removed for a maintenance outage and then re-installed. Someone thinks the fan should rotate in the opposite direction of what it should, or is looking at a direction of rotation arrow on the vent fan motor which is very often incorrect.)

Those are the most common problems for turbine compartment vent fan problems. If there is automatic change-over, then there are usually differential pressure switches to provide indication of fan discharge pressure; check to make sure they are working properly (bugs build nests in the open ports of differential pressure switches where one port is open to atmosphere). If there are gravity dampers on the fans, make sure they are properly latched in the proper position (some newer units also have limit switches to warn if the dampers are not in the proper position).

Best of luck! Please write back to let us know what you find and how you resolve the problem.
 
It sounds like the unit has redundant turbine compartment cooling fans (hence, the change-over alarm) and because they are very important for helping to remove combustible gases from the turbine compartment the Mark* was programmed to shut the unit down if there is not one turbine compartment ventilation fan running.

SOME (but not all) turbine compartment vent fans have dampers which are supposed to be latched open and gravity will close them when there is a fire and fire extinguishing agent (CO2) is discharged. Quite often, these damper latches will work themselves loose and allow the dampers to close, which will prevent proper ventilation of the turbine compartment. That's one thing to check.

Often, the turbine compartment vent fans are reverse tangential centrifugal fans--meaning they rotate in the opposite direction one would suspect they would rotate based on the angle of the vent fan blades. When this happens, too little air is moved and, usually, the vent fan motor trips on excessive current (thermal overload relay) because the motor draws excessive current when spinning in the reverse direction. DO NOT trust a direction of rotation arrow on the motor housing--there was a direction of rotation arrow painted on the fan housing by the manufacturer, and that usually gets painted over during construction. The type of fan blade determines the direction of rotation. (It's very common for the rotation to get "confused" after the motor(s) has(have) been removed for a maintenance outage and then re-installed. Someone thinks the fan should rotate in the opposite direction of what it should, or is looking at a direction of rotation arrow on the vent fan motor which is very often incorrect.)

Those are the most common problems for turbine compartment vent fan problems. If there is automatic change-over, then there are usually differential pressure switches to provide indication of fan discharge pressure; check to make sure they are working properly (bugs build nests in the open ports of differential pressure switches where one port is open to atmosphere). If there are gravity dampers on the fans, make sure they are properly latched in the proper position (some newer units also have limit switches to warn if the dampers are not in the proper position).

Best of luck! Please write back to let us know what you find and how you resolve the problem.
 
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