The shaded-pole motor is a type of single-phase induction motor widely used for various low-power applications, such as small fans, blowers, and other devices that require continuous, low-torque operation. It is relatively simple in design and construction, making it cost-effective and reliable for these applications.
The concept of a shaded-pole motor involves introducing asymmetry in the magnetic field during the motor's operation, which in turn creates a rotating magnetic field. This rotating magnetic field is necessary for the motor to start and continue its operation.
Here's how the shaded-pole motor works:
Stator Construction: The stator of a shaded-pole motor is made up of a laminated core with main and auxiliary windings. The main winding carries the primary current, while the auxiliary winding, also known as the shading coil, is placed around a portion of the pole faces (typically less than half of the pole face).
Asymmetrical Magnetic Field: When the motor is powered, the current flowing through the main winding creates a magnetic field. However, due to the presence of the shading coil, the magnetic circuit around one side of the pole becomes more magnetically conductive than the other side. This asymmetry in magnetic conductivity causes a time-delayed magnetic field on one side of the pole compared to the other.
Rotating Magnetic Field: As the magnetic field oscillates, the delayed magnetic field in the shaded portion lags behind the rest of the magnetic field. This lagging magnetic field creates a rotating effect, inducing a starting torque on the rotor. This torque initiates the rotation of the rotor, allowing the motor to start and begin its operation.
Low Starting Torque: Shaded-pole motors are known for their low starting torque compared to other motor types. This makes them suitable for applications where the load is light and the motor needs to start reliably without excessive mechanical stress.
Continuous Operation: Once the motor is started, the rotating magnetic field generated by the shaded-pole design allows for continuous operation. However, due to the inherent limitations of this design, shaded-pole motors are best suited for applications where consistent, low-torque output is required.
In summary, the concept of shading coils and the resulting asymmetrical magnetic field in a shaded-pole motor contribute to the generation of a rotating magnetic field, which in turn provides the starting torque necessary for the motor to begin its operation. While shaded-pole motors may not be suitable for high-torque applications, they are cost-effective and reliable for various low-power devices that require continuous operation with relatively low starting torque.