S7 400 Redundancy Failure of Automation Processors During Switchover


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Gas turbines have rendundant automation processsors. we switched over from Master to slave by turning off the power supply module. there is no issue and changeover was smooth without affecting the plant operation. When we switched back from standby (acting master) to master (acting slave) we lost signal to HMI(PCS7) and turbine went to unknown state (it is tripped actually).

we use PCS7 DCS. for sure there will not a trip externally.
could anyone suggests how to overcome this issue?
I understand the S7-400 in dual redundant mode takes around 25-30mins to synchronise with it's partner to achieve hot standby.

So if you have cut supply to the master, restored power then cut power to the other S7-400 in a fairly short space of time, you will lose control.


Many thanks for your reply,

we did the same as earlier and today as well. after the red lights goes off and also 15 minutes gap we did the changeover, but still it tripped the gas turbine.