Textbook Problem

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What is the operating principle of all three-phase motors?

To determine

Explain the operating principle for all three-phase motors.

Explanation of Solution

Discussion:

The three-phase AC motors work on the principle of rotating magnetic field (RMF). When the three-phase supply is connected to stator of the motor, the three-phase currents induce the three flux waves. The fluxes interact with each other and produce the RMF. The speed of the RMF is a synchronous speed.

The synchronous speed of RMF depends on the number of poles per phase and the applied voltage’s frequency. The electromotive force (EMF) is induced in the rotor conductors due to the RMF. The induced EMF on the rotor leads to the flow of current in the rotor conductors, and subsequently rotor torque is produced. The rotor rotates in the direction of RMF due to the rotor torque.

Conclusion:

Thus, the operating principle of all three-phase motors is explained.