The shaded-pole motor is a type of single-phase induction motor used primarily for low-power applications. It is a simple and cost-effective design that provides starting torque and rotation in a single direction. The concept of the shaded pole is integral to the operation of this motor.
Here's how the shaded-pole motor works and how the concept of shading contributes to its operation:
Basic Motor Operation:
Shaded-pole motors are used in applications where relatively low starting torque is required, such as small fans, blowers, and some small household appliances. The basic operation of the motor relies on the principle of electromagnetic induction. When an alternating current (AC) is supplied to the motor's stator winding, it produces a magnetic field that induces a current in the rotor winding, causing the rotor to rotate.
Shaded Poles:
The key feature of a shaded-pole motor is the presence of shading coils or copper rings placed around a portion of the motor's pole faces. These shading coils are made of a material with higher electrical resistance compared to the rest of the pole. They are typically made of copper or aluminum and are placed on the trailing side of the pole face (opposite to the direction of rotation).
Phase Shift:
When AC power is supplied to the motor, the current flowing through the shading coils creates a small phase shift in the magnetic field produced by the poles. This phase shift causes an imbalance in the magnetic field around the poles. As a result, the magnetic field on the shaded side lags behind the magnetic field on the unshaded side.
Starting Torque:
The phase shift and resulting imbalance in the magnetic field cause a rotating magnetic field to be established. This rotating magnetic field interacts with the rotor, inducing currents in the rotor windings. The interaction between the rotating magnetic field and the induced rotor currents creates a torque that initiates the rotation of the rotor.
Direction of Rotation:
The shading coils and the resulting phase shift ensure that the magnetic field on one side of the pole is stronger than the other side. This difference in magnetic field strength causes the rotor to start rotating in a particular direction. The direction of rotation is determined by the arrangement of the shading coils and the pole design.
In summary, the concept of shading in a shaded-pole motor creates a phase shift and an imbalance in the magnetic field, which generates a starting torque and initiates the rotation of the rotor. However, shaded-pole motors have limited efficiency and are generally used for small, low-power applications where precise control of speed and direction is not critical.