Can any body help for Active power trip ? how this work and why trip on active power?

Question

When reinsate of main power after a generator test run, the main braker tripped on Active power,

Answer 1

It is likely that when active power was restored, the generator did not get disconnected before active power was fed to the system. The generator and the active power could have been out of out of phase. This should not have happened. In the systems I have worked with, active power is fed through a contactor, whose coil is powered by active power. When active power fails, the contactor removes the connection between the contacts and the load. The generator starts and takes over. When active power is restored the contactor disconnects the generator output, just before its contacts bring active power back to the system.

It is fortunate that only a breaker tripped. Worse things can happen