Hi,

Is it possible (or advisable) to bypass the Fire Protection system of a Gas Turbine from Mark VI?
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Mark VI is programmed to trip the GT in case of Fire Detection (Heat Detectors) OR in case fire extinguishing (CO2 release Pressure Switch) is detected.
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The following signals appear to be the ones responsible for tripping the GT in case of fire

-L45FP_TRIP
-L5CMPST_TRP [Composite Trip from VPRO]
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Both signals go from '0' to '1' in case fire is detected and GT has to be tripped.

If we force these signals to '0'

1.Will the GT still trip in case Fire is detected or CO2 is released?

2.What other undesirable side effects might arise?

The intent behind forcing these signals would be to work on the Fire Detection system (Heat Detectors, Pressure Switches, Limit Switches) without the fear of spurious tripping of the Gas Turbine.

I understand that the answers to the above questions may vary from plant to plant as the Fire Protection scheme might not be the same everywhere, but I'm keeping my fingers crossed that I'll get sound advice. By the way the Fire Protection system at our unit has been provided by Sanco. Any help or advice will be appreciated.

 

GE fire detection system is differentiated into different zones.

axillary compartment - 2 pairs of fire detectors

turbine and exhaust compartment - 4 pairs of fire detectors

off base skid (if present) one pair of fire detectors.

these detectors are wired first into the fire detection PLC first. Here, separate logic is written to determine when to initiate the trip command / release co2 into the compartments.

an example would be that 2 out of 4 logic for the accessory compartment could be used for detecting fire.

this plc after the logic is satisfied sends command to
a. mark VI - which on receiving the signal trips the turbine.
b. to the master solenoid in the Co2 release panel.

exactly how all this is configured can only be found out if the application code can be looked into. however, there will be separate trip signals coming for fire in different zones.

eg. L45ft1x for axillary compartment
l45ftx2 for turbine compartment etc ...
these signals are then ORed to generate the master fire signal L45ftx.

regarding emergency push buttons in the field, they can be configured. they can be routed to the plc, then to mark VI, or first to mark VI itself.

one more field instrumentation regarding the fire protection is the limit switches of the co2 release panels, which indicate bank empty/not empty. they are harmless enough. you can do without any bypass, but of course operators in the control room are gonna be annoyed with the continuously incoming alarms

i would advise you to do this

a. first decide which temperature switch you are going to work on. bypass the trip of the particular trip. eg. working on auxiliary compartment. then force l45ft1x to zero.

b. remove the trip signal going to the master trip solenoid of that particular bank. eg. working on auxiliary compartment remove the master solenoid connection in the co2 release panel meant for auxiliary zone.

by doing this you will be keeping the live ones online and the maintenance ones offline.

and one more thing, it is near impossible to work on fire detectors in the turbine area when machine is running. the exhaust ones can be done with great difficulty. the only area when the work will be at ease will be in the axillary compartment. so i must ask, why exactly are you going to work in fire detectors online??

 

Thank you, Process Value.
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We had a Fire Protection tripping a few days ago. In actual there was no trip condition present, i.e. no fire and no CO2 release.

An alarm related to CO2 release had been appearing on the Fire Protection panel (PLC) prior to the tripping, the alarm appearing on Mark VI was "Fire Protection Panel Trouble", probably due to the malfunctioning of one of the Pressure switches installed on the CO2 cylinders.
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We had determined that it was a false alarm but we did not inhibit the Fire Protection trip, now in the future if such a situation arises we intend to disable the fire protection trip while remaining vigilant and work on the fire system components that are normally accessible when the GT is in operation (CO2 pressure switches or Auxiliary Compartment Fire detectors).

Thanks for the help.

 

Glad to help out , and yes thanks for the feedback.

 

Hi,

I would be cautious with simply forcing the signals on the MKVI. On our site, whilst the fire system sends trip signals to the controller, it also sends hardwired signals out to motors / fans etc. So simply forcing the MKVI may not stop the unit from tripping.

Regards

M

 

Sarmad... Have you considered the application of an M of N voting scheme for the Fire Protection system?

Regards, Phil Corso