Turndown ratio in AC motor speed control

When choosing a engine for a credit card applicatoin, a primary consideration may be the speed range it’ll be operated in. Whenever a motor is run substantially slower than its rated base speed, several potential adverse effects may come into play, including reduced cooling effectiveness, reduced power effectiveness and a modify in the motor’s rate and torque features. To mitigate this problem, some motors and speed controllers have already 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 a credit card applicatoin operates at a constant speed, the thing that is needed may be a gearbox or swiftness reducer that brings the motor speed down to the required level. Nevertheless, many applications require the acceleration of the motor to be speed reducer gearbox diverse 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 upon a variety of factors, however, it’s important to first look at the way the characteristics of a electric motor change when the speed is reduced.

A motor usually has a base speed, specific by the manufacturer, that it is certainly designed to operate at. Nevertheless, if a engine is operated below the base speed, it could experience reduced efficiency of the cooling system. Especially with generally used Totally Enclosed Fan Cooled (TEFC) and ODP (Open Drip Evidence) motors, where in fact the cooling program consists mainly of a shaft-mounted enthusiast, a reduction in speed outcomes in decreased airflow over the motor and lack of cooling, and temperature buildup occurs. Particularly when the electric motor is operated with complete torque at low speeds, heat can easily build up inside the motor to harmful levels.


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