BASIC AC THEORY 14

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AC MOTOR TYPES

Various types of AC motors are used for specific applications. By matching the
type of motor to the appropriate application, increased equipment performance
can be obtained.

 

Induction Motor

Previous explanations of the operation of an AC motor dealt with induction motors. The
induction motor is the most commonly used AC motor in industrial applications because of its
simplicity, rugged construction, and relatively low manufacturing costs. The reason that the
induction motor has these characteristics is because the rotor is a self-contained unit, with no
external connections. This type of motor derives its name from the fact that AC currents are
induced into the rotor by a rotating magnetic field.

The induction motor rotor (Figure 5) is made of a laminated cylinder with slots in its surface.
The windings in the slots are one of two types. The most commonly used is the “squirrel-cage”
rotor. This rotor is made of heavy copper bars that are connected at each end by a metal ring
made of copper or brass. No insulation is required between the core and the bars because of the
low voltages induced into the rotor bars. The size of the air gap between the rotor bars and
stator windings necessary to obtain the maximum field strength is small.

 

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