We are planning to upgrade exiting obsolete fire & Gas detection system in our Frame-6 GT to a new system. This includes the Panel, Detectors (fire, Heat and Gas), the Beacons and Sirens. As we are now writing the Scope of Work. Appreciate if I can get any advice for what I should include in the SOW. Also what about the types of detectors to be used (UV or IR for flame detection and Catalytic or IR for Gas detection)? This system will be Modbus communicated to Mark-VIe HMI. The system is from Minimax. Shall we make separate panel for fire and separate one for gas (as the existing system) or include both in one panel?

 

hany5757,

In my experience, I have never encountered a gas turbine which has experienced a compartment fire which was detected by the fire detection system and resulted in a turbine trip and the discharge of extinguishing agent. Usually, there is so much air moving through a compartment (or the doors have been left open--yes, people operate their units with compartment doors wide open) and the location of the fire was not near any of the fire detectors (typically heat-sensitive switches) so either wire melted and caused grounds/shorts which tripped the unit, or personnel noticed the fire and initiated a manual trip and discharge of extinguishing agent (and at two sites with multiple zones of fire protection, extinguishing agent was manually discharged into the wrong zones).

There have been MANY reports on MANY World Wide Web sites about false fire indications and trips and discharges of extinguishing agent due to problems with the sensitivity (over-sensitivity) and placement of IR fire detectors--LOTS of reports. They are really great in theory, but, some sites have caused trips and discharges because welding was being done in the vicinity of one or more IR detectors.

New GE-designs for compartment ventilation include hazardous gas detectors in the ductwork of compartment discharge ducts. This has several problems because many of the detectors don't work well or at all when contaminated with oil vapours and dust--and a lot of compartments have oil leaks which become vapours due to the heat in the compartment that get carried with ventilation air over the hazardous gas detectors and contaminate the detectors, making them inaccurate or incapable of detecting other hazardous gases.

Fire detection and protection is a must, and so is hazardous gas detection in many parts of the world. But, most methods have some issue which makes them not really suitable for the high temperatures and atmospheres in gas turbine compartments (including Accessory- and Load Compartments).

As with any "system" purchase, one needs to check the references of the supplier to determine if they have done similar installations and what the experiences of previous purchasers have been--from a reliability standpoint (unit reliability), equipment quality, and after-market service and support. Some systems require proprietary test equipment--which can be very expensive to purchase and maintain.

Placement of sensors must be chosen so that contamination is minimized, but also plant personnel have to be diligent with housekeeping and maintenance--both in compartments, and with the sensors. Some sensors can be contaminated by the oils on a person's hands.... So, even installing a replacement sensor requires clean gloves and care. And to determine this, one usually has to read the manuals provided with the equipment. I've seen equipment installers be unaware of the requirements for cleanliness....

Please write back to let us know how you proceed and what your experiences are while making the decision, how you arrived at your decision, and how the installation/commissioning went. Again, checking references for potential suppliers--while not fun--can prevent a lot of problems before they occur. Many suppliers/integrators simply don't experience with gas turbine applications and are ill-prepared and ill-equipped to do a proper job, both from a design standpoint as well as an installation/commissioning standpoint.

I highly suggest you also have some hardwired discrete contacts from any system you choose connected to the turbine trip circuits as well as for at least general alarms, and do not rely completely on MODBUS for alarm and tripping indications. Sure, it's great to be able to see analog sensor values on a screen--but you want to make sure that if there's some issue with MODBUS communications the unit can still be tripped, at a minimum, with a discrete signal.

Hope this helps!