When choosing a engine for an application, a primary consideration may be the speed range it’ll be operated in. Whenever a motor is operate substantially slower than its rated base speed, numerous potential adverse effects may come into perform, including reduced cooling performance, reduced power efficiency and a change in the motor’s swiftness and torque characteristics. To mitigate this problem, some motors and rate controllers have been designed especially to drive a load at low speeds with specific control.
Most domestic and industrial 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 constant speed, the thing that is required may be a gearbox or acceleration reducer that brings the engine speed down to the required level. However, many applications need the quickness of the engine to be different during operation.
This is normally achieved using a VFD or Adjustable Frequency Drive, which controls the speed by modifying the frequency fed to the motor. Deciding on the best electric motor and VFD type depends on a number of factors, however, it is necessary to 1st look at how the characteristics of a electric motor change when the rate is reduced.
A motor usually speed reducer gearbox includes a base speed, specified by the product manufacturer, that it is certainly made to operate at. Nevertheless, if a motor is managed below the bottom speed, it could experience reduced performance of the cooling system. Especially with generally used Totally Enclosed Enthusiast Cooled (TEFC) and ODP (Open Drip Evidence) motors, where in fact the cooling program consists primarily of a shaft-mounted fan, a decrease in speed outcomes in reduced airflow over the engine and loss of cooling, and temperature buildup occurs. Especially when the engine is operated with complete torque at low speeds, heat can easily build up within the motor to harmful levels.