Induction motor has two types of Rotar

Induction motor has two types of Rotar

(1) Squirrel cage rotor

(2) Wound-rotor ya Slip Ring

SQUIRREL CAGE ROTOR – The rotor winding consists of an insulated conductors, in the form of copper or aluminium bars embedded in the semi closed slots. These solids bar short circuited at both ends by end-rings of the same material for good electrical connection the bars are rivetedd, brazed or welded with the two end-rings in smaller size, below 40 kw the assembled rotor core is placed in a mould and the molten conducting material usually aluminium is forced into the slots. Thus the rotor bars end-rings and the cooling fan are cast in the operation. without the rotor core the route bars and end-rings look like the cage of a squirrel hence the name squirrel cage induction motor. Note that the rotor bars form a uniformly distributed winding in the rotor slots. As the rotor bars are short-circuited by two end-rings, No external resistance can be inserted in the rotor circuit of a squirrel cage induction motor.

Wound rotar ya slip ring –

In the wound-rotor type, the rotor slots accommodate an insulated winding similar to that used on the stator.The rotor winding is uniformly distributed and is usually connected in star. The three leads from the star connection are then connected to three slip rings or collector rings mounted on but insulated from the shaft, Carbon brushes pressing on the slip rings allow, external resistors to be inserted in series with the rotor winding for speed and starting-torque control. Actually, the wound-rotor type of induction motor costs more and requires increased maintenance; it is therefore only used where,

(1) the driven load requires
speed control or

(2) high starting torque is required.

Since the rotor is wound with polyphase windings and carries slip rings, it is called wound-rotor or slip-ring induction motor.
In both the types, the rotor slots are not parallel to the shaft axis, i.e, the rotor slots are skewed for obtaining a quieter and smoother operation of the induction motor.