From Motors and Drives

AC Motor Types

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
AC Motors
AC motors include single, multiphase, universal, induction, synchronous, and gear motors. They also include servomotors.
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.
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.
AC Servomotors
AC servomotors are responsive, high-acceleration motors typically constructed as permanent magnet synchronous motors.
Motor Starters and Contactors
Motor starters and contactors are motor-starting devices. They combine a contactor with overload protection and are designed for starting AC or DC motors.

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...

AC and DC motors are the two major types in use today that are related to the industrial and HVAC applications. These motors provide the speed, torque, and horsepower necessary to operate the...

Control of Speed, Torque, and Horsepower Control of Speed The speed of a squirrel cage motor depends on the frequency and the number of poles for which the motor is wound. The higher the frequency,...

What are the two main parts of a DC motor and what is the purpose of each? What is the purpose of the brushes? Why are the laminations in the armature skewed? What is the purpose of the...

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...