How does a shaded-pole motor achieve starting torque in a single-phase AC circuit?
1 Answer
A shaded-pole motor is a type of single-phase AC induction motor that is used primarily for low-power applications where moderate starting torque is sufficient. It achieves starting torque through a simple and ingenious design involving the use of shading coils or shading rings. These shading coils create a phase shift in the magnetic field, which in turn generates a rotating magnetic field that enables the motor to start and run.
Here's a basic explanation of how a shaded-pole motor achieves starting torque:
Stator Construction: The stator of a shaded-pole motor has a cylindrical core made of laminated steel sheets, similar to other induction motors. However, what sets it apart is the presence of small copper or aluminum coils (shading coils) strategically placed around a portion of the pole faces.
Shading Coils: Shading coils are wound around a portion of the pole faces (usually about 1/3 to 1/2 of the pole face) and are short-circuited. They are positioned in such a way that they create an asymmetrical air gap between the pole face with shading coils and the pole face without shading coils.
Starting Operation: When the motor is initially powered up, the single-phase AC voltage induces a magnetic field in the stator. The shading coils, due to their asymmetrical position and short-circuited nature, create a delay in the establishment of the magnetic field in the shaded portion of the poles.
Phase Shift: The shading coils induce a small phase shift in the magnetic field between the shaded and unshaded portions of the poles. This phase shift results in an imbalance in the magnetic field, causing the field to rotate.
Rotating Magnetic Field: The rotating magnetic field created by the shading coils produces a torque on the rotor, causing it to start moving. The rotor follows the rotating magnetic field and begins to rotate in the direction of the rotating field.
Continuous Operation: Once the rotor starts moving, it generates its own rotating magnetic field, which interacts with the stator's rotating field to produce a torque that keeps the motor running. The shading coils are primarily used for starting purposes, and once the motor is in operation, they have less influence on its performance.
It's important to note that shaded-pole motors are relatively simple and inexpensive but are not very efficient and do not provide high starting torque compared to other types of motors, such as split-phase or capacitor-start induction motors. Shaded-pole motors are commonly used in applications where low cost and moderate starting torque are acceptable, such as in fans, small pumps, and other light-duty devices.
Here's a basic explanation of how a shaded-pole motor achieves starting torque:
Stator Construction: The stator of a shaded-pole motor has a cylindrical core made of laminated steel sheets, similar to other induction motors. However, what sets it apart is the presence of small copper or aluminum coils (shading coils) strategically placed around a portion of the pole faces.
Shading Coils: Shading coils are wound around a portion of the pole faces (usually about 1/3 to 1/2 of the pole face) and are short-circuited. They are positioned in such a way that they create an asymmetrical air gap between the pole face with shading coils and the pole face without shading coils.
Starting Operation: When the motor is initially powered up, the single-phase AC voltage induces a magnetic field in the stator. The shading coils, due to their asymmetrical position and short-circuited nature, create a delay in the establishment of the magnetic field in the shaded portion of the poles.
Phase Shift: The shading coils induce a small phase shift in the magnetic field between the shaded and unshaded portions of the poles. This phase shift results in an imbalance in the magnetic field, causing the field to rotate.
Rotating Magnetic Field: The rotating magnetic field created by the shading coils produces a torque on the rotor, causing it to start moving. The rotor follows the rotating magnetic field and begins to rotate in the direction of the rotating field.
Continuous Operation: Once the rotor starts moving, it generates its own rotating magnetic field, which interacts with the stator's rotating field to produce a torque that keeps the motor running. The shading coils are primarily used for starting purposes, and once the motor is in operation, they have less influence on its performance.
It's important to note that shaded-pole motors are relatively simple and inexpensive but are not very efficient and do not provide high starting torque compared to other types of motors, such as split-phase or capacitor-start induction motors. Shaded-pole motors are commonly used in applications where low cost and moderate starting torque are acceptable, such as in fans, small pumps, and other light-duty devices.