I am working in a thermal (coal) power plant. and so I have some question about my desicion. firstly I want to know that if a unit trip from
the boiler protection or turbin protection; the breaker of field open immediately or 10 or 12 second later. main stop valves were closed
immediately or a little open began the trip for the security of balance the rotor a little second open. so our system desicion unit triped
after 12 second later circuit breaker open. is it normal or abnormal. thank you

 

Since you're coal fired, I expect that this is a fairly large generator. On a turbine trip, the OCB's should of course disconnect immediately to prevent motoring. I'm not sure about the field breakers, but I don't know why they should remain closed, especially for several seconds.

Really, you should contact the turbogenerator manufacturer and abide by their recommendations. You might also look into FOMIS (Fossil
Operation and Maintenance Information Service)at "www.scientech.com/fomis":www.scientech.com/fomis . Membership may be required, but FOMIS is a user group for fossil-fueled power plant operators. Someone with FOMIS can help you.