A shaded-pole motor is a type of single-phase induction motor that is commonly used for small appliances and devices that require low-power operation. It's a simple and cost-effective design that provides basic starting and running capabilities for various applications.
The shaded-pole motor operates on the principle of phase shifting in the magnetic field, which helps it generate a starting torque and maintain rotation. Here's how it works:
Stator Construction: The stator of a shaded-pole motor has a core made of laminated iron sheets, which creates the magnetic circuit. Around a portion of the poles, copper or aluminum shading coils (shading rings) are placed. These shading coils are responsible for the phase shift in the magnetic field.
Principle of Operation: When power is applied to the motor, a single-phase alternating current flows through the stator windings. The shading coils are positioned in such a way that they create a small time lag in the magnetic field compared to the main winding. This time lag results in a phase shift between the magnetic fields produced by the main winding and the shading coils.
Phase Shifted Magnetic Field: Due to the phase shift introduced by the shading coils, a rotating magnetic field is created in the stator. This rotating magnetic field interacts with the rotor (a squirrel-cage rotor or a shaded-pole rotor) and induces currents in it.
Starting Torque: The interaction between the rotating magnetic field and the induced currents in the rotor generates a starting torque. This torque is enough to overcome the initial inertia of the rotor and start its rotation. The rotor begins to spin in the direction of the rotating magnetic field.
Operation and Running: Once the motor starts rotating, it operates like a standard single-phase induction motor. The rotor continues to follow the rotating magnetic field produced by the main winding and the shading coils, generating the required torque to keep the motor running.
It's important to note that shaded-pole motors are relatively simple and have limited starting torque capabilities compared to other motor types, such as capacitor-start induction motors. They are mainly used in applications where the starting torque requirement is low, such as small fans, pumps, and other lightweight appliances.
In summary, the concept of shading coils in a shaded-pole motor contributes to motor starting by creating a phase shift in the magnetic field, which in turn generates the necessary starting torque to initiate rotation. While these motors are not suitable for high-torque applications, their simplicity, low cost, and reliability make them a suitable choice for certain low-power devices.