From Motors and Drives

AC Motor Types

Introduction
AC motors can be divided into two major categories-asynchronous and synchronous. The induction motor is probably the most common type of asynchronous motor (meaning speed is dependent on slip). When reviewing induction motors, there are two rating designations-NEMA and IEC.

Another type of asynchronous motor is the wound rotor motor. This type of motor has controllable speed and torque because of the addition of a secondary resistance in the rotor circuit. A third type of popular asynchronous motor is the single-phase motor. The single-phase AC motor will not be covered because of their limited use in industrial applications when connected with variable-frequency drives.

The synchronous motor is inherently a constant-speed motor, when operated directly across the line. This type of motor operates in synchronism with the line frequency. Two types of synchronous motors are non-excited and DC-excited.

The basic principles of AC induction motors have been previously covered. In this section, attention will be given to motor designations, ratings, and designs.

Standard AC Induction Motors (NEMA and IEC)
NEMA frame motors are in widespread use throughout U.S. industry. This motor design was developed before the 1950s and has well served many types of fixed-speed applications. In...


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Products & Services
Stepper Motors (rotary)
Stepper motors use a magnetic field to move a rotor in small angular steps or fractions of steps. They provide precise positioning and ease of use, especially in low acceleration or static load applications.
AC Servomotors
AC servomotors are responsive, high-acceleration motors typically constructed as permanent magnet synchronous motors.
Brushless Motors
Brushless motors are synchronous electric motors that have a magnetically (AC induction) or electronically (DC) controlled commutation system instead of a brush-based mechanical commutation system.
Motor Controllers
Motor controllers receive supply voltages and provide signals to motor drives that are interfaced to motors. They include a power supply, amplifier, user interface, and position control circuitry.

Topics of Interest

IEC Ratings At this point, it would be helpful to briefly review IEC motor ratings and then compare IEC with NEMA. The motor market today has become more global, with IEC rated motors on equipment...

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Introduction The squirrel cage induction motor is probably the most widely used motor in industry today. Traditional applications for AC induction motors include fans and pumps. The AC induction motor...