The synchronous torque developed is roughly
proportional to the angle of lag (load angle) of the
motor rotor with respect to the terminal voltage,
which, at full load, is in the area of 20 to 30
electrical degrees. If a restraining force is applied
to the motor shaft, it will momentarily slow down
until a torque is developed equal to the applied
restraint. The motor will then continue to operate
at synchronous speed