Revolving Magnetic Field
Any polyphase system, by virtue of the time displacement of the currents in the phases, makes it possible to easily generate a magnetic field that revolves at the line frequency. Such a revolving magnetic field makes polyphase induction motors possible. Indeed, where induction motors must run on single-phase power (such as is usually distributed in homes), the motor must contain some mechanism to produce a revolving field, otherwise the motor cannot generate any stand-still torque and will not start. The field produced by a single-phase winding can provide energy to a motor already rotating, but without auxiliary mechanisms the motor will not accelerate from a stop when energized.
A rotating magnetic field of steady amplitude requires that all three phase currents are equal in magnitude and accurately displaced one-third of a cycle in phase. Unbalanced operation results in undesirable effects on motors and generators.
Read more about this topic: Three-phase
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