9FA Gas Turbine Load Compartment and Turbine Compartment Excessive Ventilation


Thread Starter


Hello all

In Our 9FA machine, we have monthly schedule change over of all fans and pumps motors. Problem is, while we, change over 88BT 1/2 or 88VG 1/2 ,at MARK VIe alarm viewer " EXCESSIVE LOAD COMPT VENTL-HAZGAS PROT COMPROMISE, L30LCVFLT" and EXCESSIVE TURB COMPT VENTL-HAZGAS PROT COMPROMIZE, L30CVFLT" two alarm appeared.

I Checked logic from TOOLBOXsT already, It seems, as for example, while we change over, both 88VG fans run for (60 secs), or may be both fan hold outlet pressure for 60 secs.

My Questions are:

1. If both fans of 88VG and 88BT run for excessive time, what problem may occur? Because, as far I know, if load compartment and turbine compartment venting is too much, it should be good for those area. so, why this type of alarm is set by GE?

2. According to logic, I checked, while we change lead/ lag fan position, the fan should change over immediately. So why, also lag fan outlet pressure hold the pressure for a long time?

Thanx all

The answer to your first question is likely contained in the alarm text message: The hazardous gas detection system sensors are not rated for the extra flow created when both vent fans are running.

The answer to your second question is likely that the persons responsible for coding the alarms doesn't have any operational experience with nuisance alarms--which is what I would classify this alarm as: a nuisance. GE and packagers of GE heavy duty gas turbines have a horrible habit of not blocking alarms when it's inappropriate--such as when they have both fans running during change-over causing a higher-than-normal flow-rate which is only for a "brief" period of time.

As for why it's such a long operating overlap on changeover--again, that's for the packager of the compartment ventilation fans and ductwork to answer. There has been a LOT of CFD studies (Computational Fluid Dynamics) done on compartment ventilation and hazardous gas sensing and removal--and this has likely resulted in the "lengthy" overlap during changeover. BUT, to be sure, you need to ask this question of the packager of the compartment ventilation/hazardous gas monitoring/ductwork to be sure of the answer that's most specific to your site and it's configuration.

Hazardous gas sensing is a huge deal--think about the number of flanged fuel gas piping connections in the turbine compartment, and the number of flexible fuel gas hoses connecting manifolds to fuel nozzles. There's quite a large number of possible leaks--which can lead to quite a large explosion and fire. Hence, the need for ventilation, not so much for cooling purposes, thought that is a concern for GE-design Frame 9FA heavy duty gas turbines--but not as much as the need for safe removal of- and prevention of collection of hazardous gases in the turbine compartment where there are ignition sources.

Again, many alarms like this should be blocked such as during a changeover, but aren't. It's just plain poor programming practice, combined with a lack of concern for reducing the number of erroneous and nuisance alarms which operators of GE-design heavy duty gas turbines must live with on a regular basis.

Hope this helps!