Reluctance Torque
Any magnetic object tends to align itself in a
magnetic field so that the magnetic reluctance is at
a minimum. There are as many positions of a
salient pole rotor within the rotating stator
magnetic field as there are poles. Below
synchronous speed, a pulsating torque called
reluctance torque, is developed. It has a net
average value of zero and a frequency equal to
twice the slip frequency. This torque may lock a
lightly loaded rotor into step and develop
approximately 30% pull-out torque.