Stack dampers are commonly used in a wide range of gas turbine power plant applications. In our site we established a new stack damper and it is controlled manually.

We have two control system YOKOGOWA (DCS) & MARK VI. i am planning to configure DCS for stack damper automation and start check.

We have two auma MOV for actuating purposes and they have digital limit switches and analogue position value.

Does anyone has common logic and protection for this application?

 

I am assuming this stack damper is only closed when the gas turbine is shut down, for the purposes of bottling up the HRSG to retain heat and (maybe) to keep rain out.

Next, is the Auma actuator set up so it cannot close if there is significant airflow through it? (Recommended practice)

Typical interlocks are:
Three (3) limit switches with contacts closed when the stack damper is FULL OPEN are connected to the Mark VI as a 3 of 2 vote to trip the gas turbine any time 2 or more switches say the damper is not full open. The 2 of 3 vote should be done by the Mark VI. An alternative, assuming you have a trip command from the DCS hardwired to the Mark VI, is to connect the 3 limit switches to the DCS and do the 2 of 3 vote there and include it as one of the conditions that activate the trip command from the DCS to the GT Mark VI.
Auto close the damper on shutdown of the gas turbine after the master protection has tripped (L4X signal) AND after the turbine speed has dropped below about 150 rpm (TNH < 5% for a Frame 9 GT).

A limit switch with contacts that close when the damper is fully closed can be connected to either the Mark VI or the DCS to provide a "Fail to Close" alarm in the event the damper does not close within a suitable time (say, twice the stroke time of the damper) after being commanded to do so.

Prior to startup, the operator must fully open the damper as part of pre-start actions to bring the plant to a "Ready to Start" status.
The analogue postion signal should be connected to the DCS for display on an appropriate HMI screen.

You may also want to check with your equipment suppliers for their recommendations. Depending on the location of the damper in the stack, the HRSG supplier may want a lower turbine speed for auto closing the damper. The quoted 150 rpm value is one I have used on new applications when the damper was supplied by the HRSG supplier as part of the original installation.

Note, these are general recommendations. Best way to implement will depend on actual plant configuration and on how the Mark VI and DCS are interconnected.

 

Otised, you have pretty much described the stack damper operation at my CCGT!

I would like to emphasise Otised's point about how your DCS is connected to Mark VI. Personally, I would send the trip command from DCS via a hard-wired source, rather than rely on the DCS-Mark VI comms link.

At my site, we have three digital outputs from DCS (different I/O modules) driving three seperate trip relays. Auxilary contact off each relay are then wired in a 2oo3 configuration to send a trip request to Mark V digital input (Customer Trip). The system is designed so that in the healthy condition, each trip relay is energised, and the signal to Mark V is a logic '1.' Another relay contact off each trip relay is then wired to its own DCS digital input (again, a different I/O module) to monitor the status of the relay.

The DCS has some monitoring logic, so if one of the relay coils burns out for example, and de-energises, then a "Mismatched Unit Trip Request" alarm is generated. This has been designated a Safety System which we function test every year, during our Outage re-commissioning. It also is connected to the Customer Start inhibit too, but I can't recall off the top of my head how at the moment.

Or you could incorporate all the logic in your Mark VI.

 

If something I said in my earlier reply implied that protection signals should be connected over a data link, then I erred. Protection interlocks should always be hardwired unless there is absolutely no other way!

Your description of the protective trip signals from the DCS to the Mark V is correct. This was also done initially on Mark VI. At the time of my retirement from GE, we had changed to hardwiring each of the 3 trip relays in the DCS to the Mark VI (or Mark VIe) and doing the 2 of 3 vote within the turbine control. This means a single broken connection won't trip the turbine. (Mark VI has more I/O available than the Mark V.)