A squirrel cage rotor is the rotating part used in the most common form of AC induction motor. An electric motor with a squirrel cage rotor is termed a squirrel cage motor.
Theory ==
[[Image:Motor laminations by Zureks.jpg|thumb|right|Figure 3. Stator and rotor laminations]]
The field windings in the [[stator]] of an induction motor set up a [[rotating magnetic field]] around the [[rotor (electric)|rotor]]. The relative motion between this field and the rotation of the rotor induces [[electric current]] in the conductive bars. In turn these currents lengthwise in the conductors react with the magnetic field of the motor to produce [[force]] acting at a [[tangent]] [[orthogonal]] 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.
[[Image:Motor laminations by Zureks.jpg|thumb|right|Figure 3. Stator and rotor laminations]]
The field windings in the [[stator]] of an induction motor set up a [[rotating magnetic field]] around the [[rotor (electric)|rotor]]. The relative motion between this field and the rotation of the rotor induces [[electric current]] in the conductive bars. In turn these currents lengthwise in the conductors react with the magnetic field of the motor to produce [[force]] acting at a [[tangent]] [[orthogonal]] 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.
The iron core serves to carry the magnetic field across the motor. In structure and material it is designed to minimize losses. The thin laminations, separated by varnish insulation, reduce stray circulating currents that would result in [[eddy current]] loss. The material is a low carbon but high [[silicon]] iron with several times the resistivity of pure iron, further reducing eddy-current loss. The low carbon content makes it a magnetically soft material with low [[hysteresis]] loss.
The same basic design is used for both single-phase and three-phase motors over a wide range of sizes. Rotors for three-phase will have variations in the depth and shape of bars to suit the design classification.
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