Reverse power relay vs. Loss of excitation relay

[Minetsky]

What's the difference between the reverse power relay and loss of excitation relay on genny's. I've read that current flows towards the genny's direction but how did the device distinguish which is which??

Thanks in advance!

 

[Knobhead]

If you loose power to the field the generator becomes a motor. Loss of field current will drop out the generator > main bus breaker. It will also activate the ESD routine to protect the prime mover.
Reverse power also stops the generator drawing power from the bus.