Introduction to AC Motors for Industrial Application
AC motors are more widely used than DC motors in industrial
applications. They are available to operate on single-phase
or three-phase supply voltage systems. This allows the
motor-control designer to choose the type of motor to fit
the application. Most single-phase motors offer less than 3
HP; larger ones are not that common. Three-phase motors are
available up to several thousand horsepower, although most
that you will encounter will be less than 50 HP.
The AC motor provides several advantages over DC motors. One
advantage is the AC motor has is in its design, which has
eliminated the need for brushes and commutators by making
the field rotate and keeping the armature stationary. This
is possible in the AC motor due to the nature of the AC
supply voltage, which moves through a sine wave during each
cycle.
The sinusoidal voltage allows the magnetic field to be
created in the rotating assembly by induction rather than
the actual flow of current. This rotating field is called
the rotor in AC motors, and the stationary field is called a
stator.
The design of the rotor is different from the rotating
armature in the DC motor. Since the rotor will receive its
magnetic field by induction, it will be made completely of
laminated steel rather than having copper coils pressed on
the laminated steel. Since the rotor receives its magnetic
field by induction rather than having current flow through a
copper coil, it does not require brushes, brush riggings,
and commutators.
This permits the AC motor to operate longer than the DC
motor due to less required maintenance. This means more AC
motors are used in the industry.