Understanding the Mechanics of a Three-Phase Induction Motor: How the Rotor Rotates

In a three-phase induction motor, the rotor rotates due to the complex interplay between the rotating magnetic field generated by the stator and the

Three-Phase Supply and Rotating Magnetic Field

When a three-phase alternating current (AC) supply is fed to the stator windings, it generates a rotating magnetic field. This field rotates at a synchronous speed, which is determined by the frequency of the AC supply and the number of poles in the motor. The rotating magnetic field is a critical component in the operation of the motor, influencing the entire process of rotation.

Rotating Magnetic Field: The Heart of the Motor

The rotating magnetic field is created because the three-phase currents are out of phase with each other by 120 degrees. This phase difference results in a magnetic field that moves around the stator, creating a continuous cycle of magnetic influence that drives the operation of the motor.

Induction in the Rotor

The rotor in an induction motor is typically a squirrel-cage type or a wound-type. As the rotating magnetic field passes through the rotor, it induces an electromotive force (EMF) in the rotor conductors, as per Faraday's law of electromagnetic induction. This induced EMF results in the flow of current within the rotor conductors.

Rotor Current and Torque Production

When current flows through the rotor conductors, the interaction between this induced current and the magnetic field from the stator produces a torque. The torque is proportional to the difference between the speed of the rotating magnetic field (synchronous speed) and the actual speed of the rotor. This difference is known as the slip. The motor operates continuously as long as the three-phase AC current is supplied, maintaining a constant rotating magnetic field and sustaining the process of torque production.

Continuous Operation and Rotor Rotation

The continuous operation of the three-phase induction motor can be understood through the principle of Lenz's law, which states that the effect (torque generation) opposes the cause (magnetic field cutting by rotor conductors). To minimize the cause (flux cutting by the rotor conductors), the rotor naturally moves in the same direction as the rotating magnetic field, thus maintaining its motion.

In summary, the interaction between the rotating magnetic field generated by the stator and the induced currents in the rotor is the fundamental mechanism behind the rotation of the rotor in a three-phase induction motor. This process is a continuous and dynamic event that ensures the smooth and reliable operation of the motor in various applications.