Induction motor

The induction motor is a singly excited asynchronous machine. this motor is the first choice in the industries, leading other motors in industries for many years. induction motor is of two types single-phase induction motor and three-phase induction motors. so, how these motor works are very interesting and you get to know it in a few minutes.

the main parts of the induction motor are the rotor and stator. the stator is a stationary part of the machine which produces the main flux and, the rotor is the rotating part of the machine. the words singly excited are used because we give AC supply to the stator. two types of rotors are used in the induction motor, squirrel cage rotor, and wound rotor.

The squirrel cage rotor is a cylinder rotor consists of laminated steel sheets. the conductors made up of copper or aluminum are embedded or the surface of conductors. the conductors are shorted from both ends with the end rings. due to this, we can't add external resistance to the rotor.

Wound rotor is also called a slip-ring rotor motor because the slip rings are connected to rotor windings with the slip rings with external resistance. so, it becomes easy to control the motor. mainly squirrel rotor is used because it is cheap and it needs less maintenance. the conductor on the rotor is placed skewed but, not parallel to remove the phenomenon of crawling and cogging. Distributed winding is preferred for the winding of the stator and rotor of the induction machine.

Working of Induction Motor

When the AC supply is supplied to the stator of the induction motor. rotating magnetic field is set up in the motor. the speed of r.m.f is Ns also called synchronous speed. when this r.m.f cuts the conductors of rotor due to current is generated in the rotor conductors, due to this torque is generated and the rotor starts rotating. according to Lenz's law effect opposes its cause. in this case, the effect is torque developed in the rotor and cause is flux cutting. to oppose the cause developed torque forces the rotor to rotate in the direction of r.m.f. when this happens the flux cutting reduces.

Why rotor can't run on speed=Ns

Suppose the rotor reaches the synchronous speed, as both rotor and r.m.f are rotating at the same speed, the r.m.f can never cut the rotor. which means there is no induction effect, no currents in rotor, no torque, and hence no further rotation of the rotor.

Slip Speed

The relative speed between rotor and r.m.f is called slip speed. is Ns is the speed of r.m.f and Nr is the speed of the rotor, then the slip speed is 
             
            slip speed= Ns-Nr

Slip

In practice, we use a slip because it is a dimensionless quantity.
            
            slip= (Ns-Nr)/Ns