Hi .
I think we had here some misunderstanding
OP:
"we have a new plant in our factory it is a steam turbine which driven the generator,and it has it protection device,it`s done by Chinese engineers so they told me that the feeder of power grid should be connected always at same time with the generator while it is supplying the plant,some other peoples told me that we must have a protection device which protect the generator from the power grid like over voltage under voltage over freq. under freq. reverse power etc. so could any one help me in this issue. "
Tareksabry, as I understood, you have some generator protection, not important, what company, it;s part of generator supplier.
But you work in co-generation with the grid ( I suggest via GSU, step-up transformer).
Problem isn't generator protection, problem is loss of main protection, that means, dissconnect of grid CB on the feeding SS and fast or slow autorecloser.
Here you have so much options:
Your generator capacity is enough for plant feednig,
isn't enough, that means after decoupling from the grid, you have provide load shedding, etc.
Possible option du-feedeng, to grid and from grid.
All this points are influence on the LOSS OF MAIN protection, in lot of case it's dedicated protection and isn't part of generator protection, in the generator protection we usually use two standard protection : frequency decoupling level and ( if it request by utilities) pole slip/out-of-step.
Best Regards.
Hope that help
Slava
