How does three-phase induction motor work?

An electric motor converts electrical energy into mechanical energy which is then supplied in various types of loads. AC. Motors AC Supply and they have been classified into synchronous, single phase and 3 phase induction, and special purpose motors. Of all types, 3 phase induction motors are most widely used for industrial applications because they do not require a starting device.
In the stator of the induction motor, the angle of offset overlapping winding by an angle of 120 ° is in the stator. When the primary winding or stator is connected to the three-phase alternate from the current supply, it establishes a rotating magnetic field that rotates at a synchronous speed.
Three-phase AC induction motor rotor slip-ring and squirrel-cage induction motor are different. In the slip-ring type, the rotor consists of heavy aluminium or copper bars, which are on both sides of the cylindrical rotor. The shaft of induction motor is supported on two bearings at each end to ensure free rotation within the stator and to reduce friction. There are pieces of steel of uniformly slotted slots, which are folded around its circumference, in which un-insulated heavy aluminium or copper bars are installed.

A slip-ring-type rotor consists of three-phase windings that are internally starred at one end, and the other ends are brought out and the rotor is attached to the mounting slip ring on the shaft. And to develop a high starting torque, these windings are connected to the ricotta with the help of carbon brushes. This external resistance or rheostat is used only in the initial period. Once the motor gets normal speed, the brushes are less circulated, and the wound rotor acts as a squirrel cage rotor.

The rotation direction of the motor depends on the phase sequence of the supply lines, and in which order these lines are attached to the stator. Thus, the interchange of the connections of any two primary terminals for supply will be reversed by the direction of rotation.

The number of poles and the frequency of the applied voltage determines the synchronous speed of rotation in the stator of the motor. Motors are usually configured with 2, 4, 6 or 8 poles. Synchronous speed, the speed at which a word revolves around the area produced by primary streams, is defined by the following expression.

A rotating magnetic field in the stator is the first part of the operation. In order to produce torque and rotate in this way, rotors should take some current. In induction motors, it comes from the current rotor conductor. The rotating magnetic field produced in the stator is cut across the conductive bars of the rotor and an e.m.f.

Rotor winding in induction motor either closes through an external resistance or shuts down directly. Therefore, the motivated e.m.f stator in the rotor causes the flow in one direction in the opposite direction of the magnetic field, and in the rotor leads to a twisting speed or torque.

As a result, the speed of the rotor will not reach the same speed of r.m.f in the stator. If speed matches, then no e.m.f. Driven in the rotor, there will be no flow, and therefore no torque will occur. The difference between stator (synchronous motion) and rotor speed is called slip.
When the motor is excited by the three-stage supply, then three-stage stator winding produces a stable magnetic field in a stable quantity with 120 displacements which rotate at synchronous speed. This changing magnetic field cuts the rotor conductor and produces a stream in accordance with the principles of the rules of the electromagnetic field of Faraday. As this rotor conductor is reduced, the current flows through these conductors.


In the presence of the magnetic field of the stator, the rotor conductor is housed, and therefore, according to the Lorenz force theory, a mechanical force works on the rotor conductor. Thus, all the rotor conductor stresses, i.e., the sum of the mechanical forces produces the torque in the rotor which moves it in the same direction of the rotating magnetic field.
The rotation of this rotor conductor can also be explained by the law of lane, which states that the induced current in the rotor opposes the cause of its production, here this opposition is rotating the magnetic field. As a result, the rotor-stator rotates in the same direction of the rotating magnetic field. If the speed of the rotor is more than the speed of the stator, then no current in the rotor will be produced, because the rotor and rotator rotation is the relative speed of the magnetic field. This stator and rotor fields difference is called slip. Due to this relative speed difference between the stator and rotor, the 3-step motor is called asynchronous machine.
As we discussed above, the relative speed between the stator field and the rotor conductor causes the rotor to rotate in a particular direction.

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