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Shaded pole motor principle and characteristics

Short answer

A copper shading ring on part of each salient pole causes the shaded-pole flux to lag the unshaded flux, creating a sweeping flux wave from unshaded to shaded side that acts as a weak rotating field, starting the squirrel-cage rotor in that direction. Characteristics: low starting torque (40–50% of full-load), low efficiency and power factor, fixed direction, simple construction, used in small fans, hair driers, and clocks.

Describe operating principle and characteristics of shaded pole single phase motor with necessary diagrams.

A shaded-pole motor is a single-phase induction motor with salient stator poles, part of each pole (about one-third) being enclosed by a short-circuited copper shading ring; the rotor is a squirrel cage.

   +-------------+--------+
   |  unshaded   |[shaded]|  pole
   +-------------+--------+
        flux shifts  ----->

Principle: induced current in the ring opposes flux change, so the flux in the shaded part lags that in the unshaded part. When current rises, flux crowds into the unshaded part; near the peak it is uniform; when current falls, it crowds into the shaded part. The flux axis therefore sweeps from the unshaded to the shaded side, acting like a weak rotating field, and the rotor turns in that direction.

Characteristics:

  • Low starting torque (about 40–50% of full-load torque)
  • Low efficiency and power factor (ring losses)
  • Fixed direction of rotation; rugged, cheap, no switch
  • Used in small fans, hair dryers, toys and clocks (up to about 1/20 kW).

✓ Answer checked by Claude Sonnet 5.5

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