Q. Explain working of induction machine rotor?

The induction machine rotor may be one of two types: the wound rotor or the squirrel-cage rotor. The wound rotor has a polyphase winding similar to and wound for the same number of poles as the stator winding. The terminals of the rotor winding (wye- or delta-connected, in the case of three-phase machines) are brought to insulated slip rings mounted on the shaft. Carbon brushes bearing on these slip rings make the rotor terminals available to the circuitry external to the motor. The rotor winding is usually short-circuited through external resistances that can be varied. A squirrel-cage rotor has a winding consisting of conducting bars of copper or aluminum embedded in slots cut in the rotor iron and short-circuited at each end by conducting end rings.

The squirrel-cage induction machine is the electromagnetic machine most widely used as a motor because of its extreme simplicity and ruggedness. Although the induction machine in the motor mode is the most common of all motors, the induction machine has very rarely been used as a generator because its performance characteristics as a generator are not satisfactory for most applications; however, it has recently been used as awind-power generator. The induction machine with a wound rotor is also used as a frequency changer.