To investigate the relationship of“load” pull-intorque and “nominal” pull-in torque, assume an
application of a centrifugal fan having an inertia
factor of 20, and connected to a 1000 HP, 1200 rpm
motor. The fan load at synchronizing speed, with
closed discharge, is 50% of full load torque.
Assume it is determined that the motor slip must
not exceed 1.8% if the motor is to pull into step on
application of excitation. In this case, the effect of
reluctance torque is neglected and it is assumedfor synchronizing.
excitation may be applied at the worst phase angle