Steady-state operation of motor:
Effect of torque changes
Assuming that a synchronous motor operates
initially with a leading PF.
If the load on the motor increases, the rotor
initially slows down increasing the torque angle
δ. As a result, the induced torque increases
speeding up the rotor up to the synchronous
speed with a larger torque angle δ.
Since the terminal voltage and frequency
supplied to the motor are constant, the
magnitude of internal generated voltage
must be constant at the load changes
(EA = Kφω and field current is constant).