3 phase Induction motor Definition and Working Principle

An Electromechanical device that Transforms Electrical energy into mechanical energy is an Electrical motor. A Three-phase Induction motor is the most popular motor for Three-phase AC (Alternating Current) operation. Because it doesn’t need an Additional starting device. These motors are referred to as Self-starting Induction motors.

To get a good understanding of the Working Principle of a 3 phase Induction Motor,. It’s Essential to understand the construction of a 3 phase induction motor. The two main components of a Three-phase induction motor are:

• A stator
• A rotor

3 Phase Induction Motor Stator

The three phase induction motor’s stator is made up of numerous slots that are used to build a three phase winding circuit that is connected to a three phase AC source. When we turn on the three-phase AC supply source, we position the three-phase winding in the slots so that they create a single rotating magnetic field.

Rotor of Three Phase Induction Motor

The three phase induction motor’s rotor is made up of a cylindrical laminated core with parallel conductor-carrying slots. Heavy copper or aluminium bars that are short-circuited by the end rings and fitted into each slot serve as the conductors. The slots are slightly skewed rather than perfectly parallel to the shaft’s axis because this arrangement lessens magnetic humming noise and helps prevent motor stalling.

3 phase induction motor working principle

Production of Rotating Magnetic Field

The stator of the motor consists of overlapping winding offset by an electrical angle of 120^o. When we connect the primary winding, or the stator to a 3 phase AC source, it establishes rotating magnetic field which rotates at the synchronous speed.

Secrets Behind the Rotation:

According to Faraday’s law, an induced emf in any circuit is caused by the rate at which the magnetic flux linkage through the circuit changes. An emf is induced in the rotor copper bar as the rotor windings in an induction motor are either closed through an external resistance Or directly shorted by an end ring, cutting the stator rotating magnetic field. As a result, current flows through the rotor conductor.

Here the relative speed between the rotating flux and static rotor conductor is the cause of current generation; hence as per Lenz’s law, the rotor will rotate in the same direction to reduce the cause, i.e., the relative velocity.

Thus from the working principle of three phase induction motor,. The rotor speed should not be equal to the synchronous speed generated by the stator, it can be seen. Since there would be no relative speed if the speeds were equal, there would also be no current flowing and no induced emf in the rotor, which would prevent the generation of torque. As a result, the rotor is unable to reach synchronous speed. The slip is the difference between the rotor and stator speeds (synchronous speed). The advantage of an induction motor’s rotating magnetic field is that the rotor does not require electrical connections.

Thus the three phase induction motor is:

• Self-starting.
• Robust in construction.
• Easier to maintain.
• Economical.
• Less armature reaction and brush sparking because of the absence of commutators and brushes that may cause sparks.