If you seek comprehensive information about AC motors, you’ve come to the right place. Custom AC motors fall into two main categories: synchronous and asynchronous. The most common type of asynchronous motor is the AC induction motor, which custom motor manufacturers make using an AC transformer with a rotating secondary. In this type of motor, the primary winding, or stator, connects to the power source while the shorted secondary member, or rotor, carries the induced secondary current. The action of rotor currents on the air-gap flux produces torque. An asynchronous motor, on the other hand, is in a separate AC motor class because of the differences in design and operational characteristics.
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Additional Custom AC Motor Design Types
Polyphase AC Motors
Polyphase squirrel-cage AC motors, such as three-phase motors, are constant-speed machines. They have some degree of flexibility in operating characteristics when modifying the rotor slot design. Variations in AC motors produce changes in current, torque and full-load speed.
AC Servo Motors
Servo motors are used in AC servomechanisms and computers that require rapid, accurate response characteristics. To obtain these characteristics, servo motors have small-diameter, high-resistance rotors. The smaller diameter provides low inertia for fast starts, stops and reversals. The high resistance allows for a nearly linear speed-torque relationship for accurate control.
Multi-Speed AC Motors
Custom motor manufacturers design consequent-pole AC motors to operate at one speed. By physically reconnecting the leads, they can achieve a 2:1 speed ratio. Typical speeds for 60-Hz AC motors are:
3,600/1,800 rpm (2/4 pole)
1,800/900 rpm (4/8 pole)
1,200/600 rpm (6/12 pole)
Two-winding AC motors have two individual windings that manufacturers can wind for any number of poles to facilitate obtaining other speed ratios. Ratios greater than 1:4, however, are impractical because of an AC motor’s size and weight. Single-phase AC motors generally have a variable-torque design. However, constant-torque and constant-horsepower AC motors are also available.
Single-Phase AC Motors
Single-phase induction AC electric motors are commonly fractional-horsepower types. However, single-phase integral-horsepower is available in the lower horsepower range. The most common fractional-horsepower single-phase AC motors are:
- Permanent split-capacitor
- Shaded pole
This custom AC motor design is available in multi-speed types, but there are practical limits to the number of speeds obtained. Those with two-, three- and four-speed motors are available. Consequent-pole or two-winding methods may accompany speed selection.