If the no-load frequency of the oncoming
generator is slightly higher than the
system’s frequency, the generator will be
“floating” on the line supplying a small
amount of real power and little or no
reactive power.
If the no-load frequency of the oncoming
generator is slightly lower than the
system’s frequency, the generator will
supply a negative power to the system:
the generator actually consumes energy
acting as a motor!
Many generators have circuitry
automatically disconnecting them from the
line when they start consuming energy.