If I understand your question, what is happening is that the generator is brought to sync (voltage & frequency), then the breaker is closed and then trips free. Correct?
I would review the breaker schematic to see what relaying is connected to the trip coil. Make sure all relay targets are reset.
Is this a recent occurence? Have the relays been calibrated recently?
The information is grossly inadequate. The breaker may have some mechanical problem/pole descrepency trip. give some more details about the size,voltage level,type of protection,breaker details etec.
Sounds like one of the genrators could have the quadrature dropp CT reversed. This would cause voltage rise instead of droop. What happens is that when you synchronise everything is okay until a small load chagne occurs which triggers a huge circulating current.
Check that generator against others if you have mor than two.
Check that quadrature droop CT is in correct phase in each and check that polarity is correct.
Suggestion to the previous posting. What if there is one generator only? Also, synch relay 25 may close improperly. It may need the calibration or it is wired improperly; one contact may close the breaker and another trip it.
