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A shaded pole motor is Cheaper, Simpler, Extremely Rugged & Reliable because it does not have _________
Commutator
Capacitor
Centrifugal switch
Commutator, Capacitor, & Centrifugal switch
Commutator, Capacitor, & Centrifugal switch
A shaded-pole induction motor is a simple self-starting single-phase induction motor that employs a salient pole structure with a copper shading ring surrounding a portion of each pole. Because it operates on the principle of a rotating magnetic field created by phase displacement via the shading coil, it eliminates the need for complex mechanical or electrical starting components like commutators, starting capacitors, or centrifugal switches. This non-complex construction makes it exceptionally cheap, highly reliable, and virtually maintenance-free.
A shaded-pole induction motor is a simple self-starting single-phase induction motor that employs a salient pole structure with a copper shading ring surrounding a portion of each pole. Because it operates on the principle of a rotating magnetic field created by phase displacement via the shading coil, it eliminates the need for complex mechanical or electrical starting components like commutators, starting capacitors, or centrifugal switches. This non-complex construction makes it exceptionally cheap, highly reliable, and virtually maintenance-free.
NsтАЛ=P120fтАЛ тАФ Synchronous speed formula for induction motors
s=NsтАЛNsтАЛтИТNтАЛ тАФ Slip ratio of the motor
When AC supply is applied to the main winding, an alternating flux is induced in the pole core. A part of this flux links with the short-circuited copper shading ring, inducing an eddy current in it. By Lenz's law, this induced current opposes the main flux change in the shaded portion, creating a time delay (phase shift) between the fluxes in the unshaded and shaded regions. This phase displacement produces a weak shifting or rotating magnetic field that moves from the unshaded part toward the shaded part, developing the starting torque necessary to rotate the squirrel-cage rotor.
Starting torque is low (around 40% to 50% of full-load torque).
Efficiency is extremely low (typically 5% to 35%).
Power factor is low (around 0.5 to 0.6 lagging).
Direction of rotation is fixed from the unshaded segment toward the shaded segment of the pole.
Extremely economical to manufacture and low initial cost
Highly robust construction with no moving mechanical contacts or switches to wear out
Extremely reliable and low maintenance requirements
Very low starting torque
Poor overall efficiency and high internal losses
Fixed direction of rotation (cannot be electrically reversed easily)
Small electric fans, blowers, and exhaust fans
Record players, hair dryers, and slide projectors
Small appliances such as clocks and refrigerator defrost timers
Option A (Commutator) is used in DC motors and universal motors, not single-phase induction motors.
Option B (Capacitor) is used in capacitor-start or capacitor-run single-phase induction motors to provide a 90┬░ phase shift.
Option C (Centrifugal switch) is used in split-phase and capacitor-start induction motors to disconnect the starting winding once the motor reaches ~75% of full speed.
Option D is correct because a shaded pole motor entirely eliminates all three components, making it simple and reliable.
D is correct тАФ A shaded pole motor contains no commutator, capacitor, or centrifugal switch, giving it an extremely simple, rugged, and low-cost construction.
In competitive exams, remember that the direction of rotation in a shaded pole motor ALWAYS goes from the UNSHADED part to the SHADED part of the pole piece.