Motor types for low speed running
The Motor will be either IC 416 or IC 616 or IC 666. In these types of cooling, external fan is not mounted on the motor shaft and totally independent, which is designed to remove the heat / losses from the motor at reduce speed. Normally during low speed motor fan which mounted on motor shaft is not sufficient to remove the complete heat so this external mounted fan removes the heat from the motor. Incase these external fan is not required, motor can designed with higher frame, which means compromising with the motor efficiency.