which dcs is better for coal fired sub critical thermal power plant do you think?

ABB 800XA ,siemens 3000T ,foxboro ,GE or another one which you can offer.
 

You can make any one of those, or other such as Emerson DeltaV, Honeywell Experion, Yokogawa, or even a PLC, do what you want them to.

If this is a green field project, I recommend short interviews with the companies that have service in your area.  From this, shorten the list to 2-4 systems, then perform an analysis to see how each compares to a 'wish list' you develop.

If this plant is a part of a bigger company (not stand alone), then there may be some benefits of using the DCS the company is already using.  

______________________________________________________________________________
This is normally the space where people post something insightful.

Look for a manufacturer with a history of power applications. Delta V and Experion are primarily process industry systems - someone with turbine control experience would be the logical choice, so the Siemens and GE systems plus Emerson's (formerly Westinghouse's) Ovation system would all be good choices. You really do not want to have the turbine controls on one platform and balance of plant on another. I know they will communicate at some level or other but the result is never as good a design as a single-platform solution.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

controlnovice and ScottyUK thanks for helping.

 Do you have any ABB 800 XA experience? I discuss with ABB engineers and ı didnt satisfied.Usually ABB experienced with Natural Gas power plant . But our project 350 MW cola fired...
  ı agree with ScottyUK Siemens or Ge are good choise ,but if you have any experience with others DCS ı wish to hear.Sometimes catalog spesification may satisfied but practise is not.

No, I have no direct experience on ABB's ocntrol system. I do have a long and satisfied history on Westinghouse's WDPF system which was the predecessor of Ovation. I have a more limited experience with Ovation but have been impressed by the quality of the equipment and with the ability of the personnel at both the Pittsburgh and Warsaw offices.

If you use a GE turbine then go with a GE DCS because you will never get GE to use anything but their own control system for the turbine and there are strong reasons to keep a single automation platform throughout the plant. Siemens Westinghouse might well offer an Ovation system because of the historical relationship from Westinghouse days while Siemens in Germany will offer a Siemens system. MHI will likely offer Ovation, I think Toshiba have their own system, and I don't know what Alstom are currently favouring. Hopefully their accursed MicroREC is consigned to history.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

ScottyUK does bring up an excellent point.  Find a vendor with turbine control experience, and build the plant on that base.

Can't help with that.  I've been out of the power industry for 20 years.

______________________________________________________________________________
This is normally the space where people post something insightful.

You might like to know Emerson's Ovation systems are ranked #1 for control of coal fired units in the US. Go out to their website and review the project abstracts and check out what projects they have been awarded recently. It may help in selecting a system.
http://www2.emersonprocess.com/en-US/brands/ovation/Pages/index.aspx

We are currently replacing a GE Mark II turbine control with an Emerson Ovation system on a 700 MW coal fired sub crit; have done many just like it without problem. Emerson has good, DEDICATED turbine control engineers/specialists.

I especially like Ovation's turbine specific hardware which means we don't have to shop ala carte for speed cards, LVDT drivers, redundant servo cards etc; Ovation integrates them all.

ABB's 800xA is a derivative of the Bailey Network 90/Infi 90 product line which was originally (80's) sold on the strength of steam plant application specific controllers/algorithms.

A DCS, and any control system, is worth about as much as the local support.

KiwiMace
You say that "ABB's 800xA is a derivative of the Bailey Network 90"
I beg to differ. It is much more related to ABB's Sattline product from Sweden. Sattline is an object oriented DCS unlike Network 90, and so is 800xA.  

FrancisL: I clearly forgot to put on my hubble telescopes when I made that comment.

"The Harmony/INFI 90 traces its roots back to Bailey Control's 1980 introduction of its Network 90 System. In 1988, the Network 90 evolved into the INFI 90 system, then to INFI 90 OPEN system in 1992, and then to Harmony/INFI 90 System in 1996...

(Here's the good bit)

...In 2003, the Harmony/INFI 90 System began its next advancement in the evolution process with the introduction of Industrial IT System 800xA..."

http://www.abb.com/product/us/9AAC115763.aspx
 

They (ABB) do not make a song and dance about the Sattline roots

Francis
www.controldraw.co.uk
www.s88control.blogspot.com