One sectioned 2 HP induction motor with cast aluminium squirrel cage motor.

The 3-phase squirrel-cage rotor induction motor. This type of machine is very widely used since it is of rugged construction; and needs less maintenance as it has no electrical connections to the rotor and therefore no commutator or slip rings.

Its early practical development was largely due to Dobrowolsky, who in 1889 invented the squirrel cage rotor, and in 1891 showed a three-phase 100 horse power motor at the Frankfurt Exhibition.

This modern 2 H.P. 3 phase squirrel-cage rotor induction motor has been sectioned to show construction, but could still operate on no load from the magnetic field produced by the stator coils remaining uncut.