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Damper closing feedback
In simple cycle gas fired turbine, if fire takes place all dampers should close. Present system not having any feedback from the dampers whether it closed or not if fire happened.

Dear All,

Hi, We are running GE designed simple cycle gas turbine, Frame-6B & 9E. In simple cycle gas fired turbine, if fire takes place all dampers should close. Present system not having any feedback from the dampers whether it closed or not if fire happened. Will it be useful if provide feedback instrument in damper??

Thanks
G.Rajesh
I & C Engineer.

1 out of 1 members thought this post was helpful...

What problem are you trying solve by adding additional instrumentation and possibly sequencing (alarms? interlocks?) to the turbine control system?

Is there some requirement by the insurance company or local fire agency to have indication that the gravity operated dampers closed when a fire was detected and the turbine was tripped?

Have dampers closed when the unit was running that resulted in high compartment temperatures?

Or did someone fail to reset the dampers after a fire or fire protection system test or after a maintenance outage resulting in high compartment temperatures?

Sure, it would be "nice" to have some kind of indication if the dampers were open and/or closed when they should be open or closed, but adding instrumentation and sequencing and/or alarms could result in some unwanted nuisance alarms or unavailability (if someone went so far as to use the additional instrumentation to prevent a start if the dampers weren't in the proper position, or to initiate a shutdown if they changed position when they shouldn't, etc.).

Be very specific when you want to add instrumentation and sequencing and alarms for a purpose like this. Do you want redundant limit switches? Do you want start-check permissives? Do you want shutdowns?

Choose high-quality devices with stable attachment and mounting options.

Adding additional wiring and conduit can be challenging and costly, not to mention increasing the work during a maintenance outage if the new devices have to be removed to gain access to a compartment.

This seems like a simple idea, but it can quickly morph into something which can lead to reliability and availability issues.

So, define your goals and objectives; choose your instrumentation wisely (quality devices and mounting/attachment methods); and route your conduit and wiring so as not to increase work during a maintenance outage (as best as possible).

Or, you could end up with unintended problems as a result.

Some people claim that some systems are designed with minimal instrumentation. That is generally intentional, for reliability and availability reasons, but not always (it's sometimes done for cost reduction purposes). Adding instrumentation can improve some operational aspects, if done correctly. If not done correctly, with specific goals in mind and with proper attention paid to the details of mounting and attachment and routing of conduit and wiring the "simple" can be become very complicated and problematic.

I am not 100% agree with you.

First you are talking about gravity damper. usually for the fire and gas system this is NOT a gravity damper which is used but a CO2 activated damper. When CO2 release it close All Inlet and outlet Dampers on ALL enclosure of the turbine to avoid any air (and therefore oxygen) to get in and to get the CO2 more efficient inside the closed enclosures (we try to maintain a minimum of 30% CO2 concentration during 30 minutes at least).

At the same time all ventilations fans or extractors (such as oil mist eliminator) should also immediately stop for the same reason (avoid any oxygen to maintain the fire.

Why I am not agree with you is because of these ventilation fans. as the CO2 activated dampers should be manually and NOT automatically reset it is easy to forgot to reset them (especially also because they are not easy to access)and of course this is absolutely forbidden to start ventilation fans with those dampers closed. therefore the dampers position feedback is a permissive to start both for the fans and for the turbine in GE philosophy as you said obviously it will result in high temperature in compartments as the ventilations fans will blow on a closed conduit. i am not sure they will blow for very long time anyway, but no air flow in the compartments for sure

Where I am agree with you is of course that this will require some extra equipments. switches (usually magnetic limit switches same type as for the enclosure door position), tubing, wiring, input card, connection sequence in mark and definitely will have an impact on the reliability and maintenance of the whole system.

I am quite surprised that for a new installation especially with such a big turbine. Rajesh is talking about frame 9E! it is not part of the project as it seems to be a basic configuration for GE projects even for smaller turbines such as Frame 3 and frame 5. in fact this as no relation with the size of the turbine but the overall philosophy of the fire and gas system and the ventilation system as i explained above.

let me know if you are agree with what i just said

I have never seen a damper that was closed by CO2 pressure. Some dampers are manually latched open and the latch is released when CO2 pressurizes the line on discharge. And gravity then closes the damper. Other dampers are opened by air flow, and when the fans shut down gravity closes them also.

I have been to two sites where they attempted something similar and both wanted the limit switches and logic removed because they caused nuisance alarms and prevented starts. And both times the problems were directly related to the type of limit switches that were chosen and the way they were installed. But the Managers insisted the switches and logic be removed.

And both sites installed the switches and added the logic because they forgot to latch the dampers and damaged wiring and Speedtronic control panel cards due to shorts and grounds, when they ignored the high compartment temperature alarms.

Some people just weren't meant to operate turbines.

And everyone is entitled to their own opinion. 100% agreement is not necessary as G. Rajesh was just asking for opinions. Now he has two.

By J Mitchell on 3 August, 2017 - 6:09 pm
1 out of 1 members thought this post was helpful...

>I have never seen a damper that was closed by CO2
>pressure. Some dampers are manually latched open and the
>latch is released when CO2 pressurizes the line on
>discharge. And gravity then closes the damper. Other dampers
>are opened by air flow, and when the fans shut down gravity
>closes them also.

To be fair, the dampers and CO2 fire doors (cooling air flow from generator through the load compartment, then out dampers) ARE actually closed by CO2. They are still gravity closed, but all have a "pressure switch" that is a latch that keeps them open. Spring pressure on the internal piston pushes a latch pin out that catches the latch to keep it open. When CO2 pressurizes the discharge header of the Fire Suppression system, the pressure is sent to these "pressure switches". The stem is hollow allowing CO2 to pass through to the opposite side of the piston causing the pin to retract as the piston is moved. The pin disengages with the latch, allowing counterweights (dampers) and spring-assisted gravity (Fire Door) to slam shut.