Distorted Field Motor or Shaded Poles

The distorted field electric motor stands out among the single-phase induction motors for its starter process, which is the simplest, most reliable and economical. Its construction is composed of three types: outboard poles, skeleton type and distributed windings. One of the most common forms is that of protruding poles, where it is observed that a part of each pole, generally 25% to 35% thereof, is embraced by a shorted copper loop.

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The current induced in this loop causes the flow through it to suffer a delay in relation to the flow of the part not embraced by the same resulting in the resemblance to a rotating field that moves in the direction of the unclosed part to the embraced part of the pole , producing torque that will cause the motor to start and achieve rated speed. The direction of rotation, therefore, will depend on the side where the part of the pole is located. Consequently, the distorted field motor has a single direction of rotation and can generally be inverted by changing the position of the rotor shaft tip relative to the stator. Other methods for rotational inversion are possible, but they become prohibitively expensive.