The AC Induction Motor (ACIM) is one of the most popular motors used in consumer and industrial applications. The motor is cheap to manufacture and has high reliability because there are no brushes to wear out. On the downside, it is less efficient than other motor types. At least 90% of industrial drives have induction motors; this is a result of its robustness and low cost. Another important aspect is the low maintenance price which is a consequence of its simple and reliable design. An additional key factor is that the rotor does not have any moving contacts, which eliminates sparking.
Key characteristics of the AC Induction Motor:
- Low Cost to manufacture
- Simple, low-cost design for fixed-speed applications
- Lower efficiency than other motor types
- Speed proportionate to line frequency (50 or 60 Hz)
- Complex control for variable speed and torque
The AC Induction Motor, sometimes called a squirrel cage motor, is comprised of a simple cage-like rotor and a stator containing three windings. The changing field produced by the AC line current in the stator induces a current in the rotor which interacts with the field and causes the rotor to rotate. No brushes are necessary in this design. The base speed of the AC motor is determined by the number of poles built into the stator windings and the frequency of the AC input voltage. Variable speed control of an AC motor can be accomplished by increasing or decreasing the input frequency.
A load on the motor causes the motor to “slip” in proportion to the load. The slip occurs when the rotor turns at a slower speed than the rotating field produced by the stator. This slip is responsible for energizing the rotor. The ACIM is available in single-phase and 3-phase versions. A 3-phase ACIM is usually the best choice for variable speed applications. For variable speed and torque, things get more complicated.