Turndown ratio in AC motor speed control

When choosing a engine for a credit card applicatoin, a primary consideration is 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 effectiveness, reduced power effectiveness and a modify in the motor’s quickness and torque characteristics. To mitigate this problem, some motors and rate controllers have already 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 is speed reducer gearbox determined by the frequency of the supply power. When a credit card applicatoin operates at a continuous speed, the thing that is required may be a gearbox or velocity reducer that brings the motor speed down to the required level. Nevertheless, many applications need the quickness of the engine to be varied during operation.

This is normally achieved using a VFD or Variable 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 rate is reduced.

A motor usually has a base speed, specified by the manufacturer, that it is definitely designed to operate at. However, if a electric motor is managed below the base speed, it could experience reduced performance of the cooling system. Especially with typically used Totally Enclosed Fan Cooled (TEFC) and ODP (Open Drip Evidence) motors, where in fact the cooling system consists primarily of a shaft-mounted fan, a reduction in speed results in reduced airflow over the electric motor and loss of cooling, and temperature buildup occurs. Particularly when the electric motor is operated with complete torque at low speeds, heat can quickly build up inside the motor to harming levels.

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