Control system design

[tsenguun odgerel]

I'm working at Power plant.
Our power station have 3 boilers and 3 turbines.
3 turbines are controlled by 2 redundant plc
and 3 boilers are controlled by 2 redundant plc
Then i don't make any sense why 3 boilers controlled by one system.

i thinks our system is being high risk.
because if boiler's redundant plcs will stop. our all boiler shut off.

i think 1 boiler should controlled by one individual system.
and boilers control should be independent.

i dont know what other industries control system design.
please help me to give advice.

 

[cjd1965]

You need to look up what a redundant PLC is, and this will answer your question

 

[GTUnit]

All your boilers are running from 1 PLC. The second PLC is the Backup.
If PLC 1 fails and stops running then all control and the process switches to the second Backup PLC and the system continues running.

You can then replace the bad PLC while all boilers continue to run with no down time.

 

[arlenjacobs]

It is about reducing risk and downtime.
Could you run with only 2 boilers? or only 2 turbines online? The redundant PLC system might be lower risk, given how unlikely it is for both to fail at the same time.
There are other things that can affect redundancy; communications network, power, I/O...

If you have unlimited money and time, sure make everything redundant. But it sounds like when your boiler system was created they wanted to only buy 2 PLCs instead of 3 (or 6 if they wanted redundancy). The redundant PLCs seem fine to me.

Assuming your redundant PLC system is going to work well, I would look at the comms network (Ethernet?) and power sources.
Make sure that the two PLCs use different Ethernet paths to anything critical
and they have different power sources.

Ex. what happens if the only Ethernet switch does down? same power supply for both PLCs?