22-12-2014, 02:18 AM
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induction motor working principle ppt in hindi
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17-03-2017, 12:07 PM
An induction motor or three-phase induction motor is an AC electric motor in which the electric current in the rotor necessary to produce the torque is obtained by electromagnetic induction of the magnetic field of the stator winding. Therefore, an induction motor can be made without electrical connections to the rotor. [A] The rotor of an induction motor can be winding type or squirrel cage. Three-phase induction motors with squirrel cage are widely used in industrial drives because they are robust, reliable and economical. Single-phase induction motors are widely used for smaller loads, such as appliances such as fans. Although traditionally used in fixed speed service, induction motors are increasingly used with variable frequency drives (VFD) in variable speed service. VFDs offer energy-saving opportunities that are especially important for existing and potential induction motors in centrifugal fan, pump and variable torque compressor applications. Squirrel cage induction motors are widely used in fixed speed and variable frequency (VFD) applications.
Operating principle
In both induction motors and synchronous motors, the AC power supplied to the motor stator creates a magnetic field that rotates over time with AC oscillations. While the rotor of a synchronous motor rotates at the same speed as the stator field, the rotor of the induction motor rotates at a slower speed than the stator field. Therefore, the magnetic field of the induction motor stator is changing or rotating relative to the rotor. This induces an opposite current in the rotor of the induction motor, in effect the secondary winding of the motor, when the latter is short-circuited or closed through an external impedance. The rotating magnetic flux induces currents in the rotor windings; In a manner similar to the currents induced in the secondary winding (s) of the transformer. The currents in the rotor windings in turn create magnetic fields in the rotor that react against the stator field. Due to the law of Lenz, the direction of the magnetic field created will be such that it opposes the change of current through the rotor windings. The cause of the induced current in the rotor windings is the magnetic field of the rotating stator, so that to oppose the change in the currents of the rotor winding, the rotor will begin to rotate in the direction of the magnetic field of the rotating stator. The rotor is accelerated until the magnitude of the induced rotor current and torque balance the applied load. Since rotation at the synchronous speed would result in no induced rotor current, an induction motor always runs slower than the synchronous speed. The difference, or "slip," between the actual speed and the synchronous speed varies from about 0.5 to 5.0% for the standard B-curve induction motors of the design B. The essential character of the induction machine is Which is created only by induction instead of separately excited as in synchronous or DC machines or self-magnetizing as in permanent magnet motors.
![[Image: 220px-Asynchronmotor_animation.gif]](https://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Asynchronmotor_animation.gif/220px-Asynchronmotor_animation.gif)
frequency of stator field and the rotor.
![[Image: 220px-Rotatingfield.png]](https://upload.wikimedia.org/wikipedia/commons/thumb/a/a6/Rotatingfield.png/220px-Rotatingfield.png)
provides a rotating magnetic field
in an induction motor.
In order for the rotor currents to be induced, the speed of the physical rotor must be less than that of the rotating magnetic field of the stator ({displaystyle n_ {s}}}; Otherwise the magnetic field would not move relative to the rotor conductors and no currents would be induced. As the rotor speed falls below the synchronous speed, the rotational speed of the magnetic field in the rotor increases, inducing more current in the windings and creating more torque. The relationship between the rotational speed of the magnetic field induced in the rotor and the speed of rotation of the rotating field of the stator is called sliding. Under load, the speed decreases and the slip increases enough to create enough torque to turn the load. For this reason, induction motors are sometimes called asynchronous motors. An induction motor can be used as an induction generator, or it can be unwound to form a linear induction motor that can directly generate linear motion.
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