|
Adjustable Speed Drive
Armature
Ball Bearing Motor
Brush
Brushed DC Motor
Brushless DC Motor
Commutator
DC motor
Direct Torque Control
Direct on Line Starter
Doubly-fed machine
ESC
Electrostatic Motor
Enameled Wire
Induction Motor
Inverter AC/DC
Linear Motor
Lynch Motor
Motor Controllers
Motor Soft Starter
Outrunner
Parvalux
Piezoelectric Motor
Repulsion motor
Shaded Pole Motor
Slip Ring
Squirrel-Cage Rotor
Stepper Motor
Traction Motor
Ultrasonic Motor
Vibrators
|
Squirrel Cage Rotor
An electric motor with a
squirrel cage rotor is sometimes called a squirrel cage motor. A
squirrel cage rotor is the rotating part commonly used in an AC
induction motor. In overall shape it is a cylinder mounted on a shaft.
Internally it contains longitudinal conductive bars of aluminum or
copper set into grooves and connected together at both ends by
shorting rings forming a cage-like shape. The name is derived from the
similarity between this rings-and-bars winding and a hamster wheel.
The squirrel-cage rotor field windings in the stator of an induction
motor set up a rotating magnetic field around the rotor. The relative
motion between this field and the rotation of the rotor induces
electrical current flow in the conductive bars. In turn these currents
flowing lengthwise in the conductors react with the magnetic field of
the motor to produce force acting at a tangent to the rotor, resulting
in torque to turn the shaft. In effect the rotor is carried around
with the magnetic field but at a slightly slower rate of rotation. The
difference in speed is called “slip” and increases with load.
The conductors are often skewed slightly along the length of the rotor
to reduce noise and smooth out torque fluctuations that might result
at some speeds due to interactions with the pole pieces of the stator.
The number of bars on the squirrel cage determines to what extent the
induced currents are fed back to the stator coils and hence the
current through them. The constructions that offer the least feedback
employ prime numbers of bars.
Use in synchronous motors
Synchronous motors must use other types of rotors although they may
employ a squirrel cage winding to allow them to reach near-synchronous
speed while starting. Once operating at synchronous speed, the
magnetic field is rotating at the same speed as the rotor, so no
current will be induced into the squirrel cage windings and they will
have no further effect on the operation of the synchronous motor.
|
|
