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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. A rotating magnetic field of steady amplitude requires that all three phase currents be equal in magnitude, and accurately displaced one-third of a cycle in phase.
An important class of three-phase load is the electric motor. A three-phase induction motor has a simple design, inherently high starting torque and high efficiency. Such motors are applied in industry for many applications. A three-phase motor is more compact and less costly than a single-phase motor of the same voltage class and rating, and ...
The three-phase induction is now used for the vast majority of commercial applications. [57] [58] Mikhail Dolivo-Dobrovolsky claimed that Tesla's motor was not practical because of two-phase pulsations, which prompted him to persist in his three-phase work. [59] The General Electric Company began developing three-phase induction motors in 1891 ...
For example; a single-phase motor with 3 north and 3 south poles, having 6 poles per phase, is a 6-pole motor. A three-phase motor with 18 north and 18 south poles, having 6 poles per phase, is also a 6-pole motor. This industry standard method of counting poles results in the same synchronous speed for a given frequency regardless of polarity.
A linear induction motor (LIM) is an alternating current (AC), asynchronous linear motor that works by the same general principles as other induction motors but is typically designed to directly produce motion in a straight line. Characteristically, linear induction motors have a finite primary or secondary length, which generates end-effects ...
The winding phases of the 3-phase motor must be energized in a sequence for a motor to rotate, for example the phase V lagging phase U by 120°, and phase W lagging the phase V (U > V > W, normal phase rotation, positive sequence). If the sequence is reversed (W < V < U), the motor will rotate in the opposite direction (negative sequence).
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A three-phase induction motor can be run at two-thirds of its rated horsepower on single-phase power applied to a single winding, once spun up by some means. A three-phase motor running on a single phase cannot start itself because it lacks the other phases to create a rotation on its own, much like a crank that is at dead center.