When choosing a motor for an application, a primary consideration is the speed range it’ll be operated in. Whenever a motor is run substantially slower than its rated base speed, numerous potential adverse effects will come into play, including reduced cooling efficiency, reduced power performance and a change in the motor’s velocity and torque characteristics. To speed reducer gearbox mitigate this problem, some motors and quickness controllers have been designed especially to drive lots at low speeds with precise control.
Most domestic and commercial motor applications use 3-phase asynchronous induction motors, which operate at a speed that’s dependant on the frequency of the supply power. When an application operates at a continuous speed, the thing that is necessary may be a gearbox or speed reducer that brings the electric motor speed down to the required level. Nevertheless, many applications need the velocity of the electric motor to be various during operation.
This is usually achieved utilizing a VFD or Adjustable Frequency Drive, which controls the speed by modifying the frequency fed to the motor. Choosing the right motor and VFD type depends upon a variety of factors, however, it’s important to 1st look at how the characteristics of a motor change when the acceleration is reduced.
A motor usually has a base speed, specified by the manufacturer, that it is definitely made to operate at. However, if a electric motor is operated below the bottom speed, it may experience reduced performance of the cooling system. Especially with commonly used Totally Enclosed Fan Cooled (TEFC) and ODP (Open Drip Proof) motors, where the cooling program consists mainly of a shaft-mounted fan, a reduction in speed results in decreased airflow over the electric motor and lack of 
cooling, and warmth buildup occurs. Especially when the motor is operated with full torque at low speeds, heat can easily build up in the motor to harmful levels.