Why is a squirrel‑cage rotor commonly called a cage rotor?

Why is a squirrel‑cage rotor commonly called a cage rotor?

• A. The rotor bars form a closed path through end rings
• B. The rotor contains windings on the rotor
• C. The rotor uses permanent magnets
• D. The rotor has no bars at all

Answer: (A)

The name comes from how the rotor is built. In a squirrel-cage rotor, conducting bars (usually aluminum or copper) are embedded in the laminated rotor core and connected at both ends by end rings. Those bars and end rings form a set of closed conducting loops around the rotor, which looks and behaves like a cage. When the stator’s rotating magnetic field sweeps past, currents are induced in these closed loops. The resulting rotor currents interact with the stator field to produce torque, causing the rotor to rotate in step with the field. That cage-like, shorted-loop structure is why this type of rotor is called a cage rotor. There aren’t rotor windings in this design—those windings belong to wound-rotor types—or permanent magnets. The bars are essential, so the other descriptions don’t fit what a squirrel-cage rotor is.

The name comes from how the rotor is built. In a squirrel-cage rotor, conducting bars (usually aluminum or copper) are embedded in the laminated rotor core and connected at both ends by end rings. Those bars and end rings form a set of closed conducting loops around the rotor, which looks and behaves like a cage.

When the stator’s rotating magnetic field sweeps past, currents are induced in these closed loops. The resulting rotor currents interact with the stator field to produce torque, causing the rotor to rotate in step with the field. That cage-like, shorted-loop structure is why this type of rotor is called a cage rotor.

There aren’t rotor windings in this design—those windings belong to wound-rotor types—or permanent magnets. The bars are essential, so the other descriptions don’t fit what a squirrel-cage rotor is.