Steady-state operation of motor:
Effect of field current changes
When the projection of the phasor EA onto
Vφ (EAcosδ) is shorter than Vφ, a
synchronous motor has a lagging current
and consumes Q. Since the field current is
small in this situation, the motor is sais to
be under-excited.
When the projection of the phasor EA
onto Vφ (EAcosδ) is longer than Vφ, a
synchronous motor has a leading
current and supplies Q to the system.
Since the field current is large in this
situation, the motor is sais to be overexcited