(a) Construction of a Squirrel Cage Induction Motor

A squirrel cage induction motor is a robust and reliable AC motor in which the rotor resembles a squirrel cage, giving the motor its name.

Main Components

1. Stator (Stationary Part)

• Composed of a laminated steel core enclosed within a rigid frame.
• The core contains slots that house the three-phase stator windings.
• When connected to a three-phase supply, these windings produce a rotating magnetic field (RMF).

2. Rotor (Rotating Part)

• Constructed from a laminated steel core with aluminium or copper conductor bars placed in longitudinal slots.
• These rotor bars are short-circuited at both ends by end rings, forming a closed “squirrel cage” structure.
• There is no external electrical connection to the rotor.

3. Air Gap

• A small uniform clearance between the stator and the rotor.
• Allows free rotation of the rotor while minimizing magnetic losses.

4. Shaft and Bearings

• The rotor assembly is mounted on a central shaft.
• The shaft is supported by ball or roller bearings for smooth rotation.

5. End Shields and Cooling System

• End shields enclose the motor and support the bearing housings.
• An external or shaft-mounted cooling fan forces air over the motor’s external cooling fins to dissipate heat.

Characteristics

• Simple and rugged construction.
• Low maintenance requirements due to the absence of brushes or slip rings.
• Fixed rotor resistance, giving relatively fixed-speed operating characteristics.