Introduction
Shaded pole induction motor is one of the simplest and most economical types of single-phase induction motors. It is commonly used in low-power applications where cost and simplicity are more important than performance. These motors are easily recognizable due to the copper shading rings placed on a portion of the stator poles.
Construction of Shaded Pole Induction Motor
The major components of a shaded pole induction motor are:
- Stator: Contains salient poles (protruding) with a portion of each pole wrapped with a copper ring called the shading coil or shading band.
- Shading Coil: A short-circuited copper ring or coil placed on a small part of the stator pole. It creates a phase shift in magnetic flux to produce a rotating field.
- Rotor: Squirrel cage type, placed inside the stator. No external electrical connection is required.
Working Principle
When a single-phase AC supply is given to the stator winding, alternating magnetic flux is produced in the pole. The shading coil delays the flux in the shaded portion of the pole. This time-lag between flux in shaded and unshaded parts creates a weak rotating magnetic field which is sufficient to produce a starting torque and rotate the rotor in one direction (from unshaded to shaded part).
Advantages of Shaded Pole Induction Motor
- Simple construction
- Very low cost
- Reliable and maintenance-free
- Works directly on AC supply
- Compact size and low noise
Disadvantages
- Low starting torque
- Poor efficiency
- Not suitable for variable load
- Rotation direction is fixed (cannot be reversed easily)
Applications of Shaded Pole Induction Motor
- Table fans
- Electric clocks
- Hair dryers
- Exhaust fans
- Refrigerator fans
- Record players
Comparison with Other Single-Phase Motors
| Motor Type | Starting Torque | Efficiency | Cost |
|---|---|---|---|
| Shaded Pole | Very Low | Poor | Very Low |
| Split Phase | Moderate | Moderate | Medium |
| Capacitor Start | High | Good | High |
FAQs
Q1. What is the direction of rotation in a shaded pole motor?
Ans: The motor always rotates from the unshaded part of the pole to the shaded part due to the rotating magnetic field produced.
Q2. Why is starting torque low in shaded pole motors?
Ans: Because the rotating magnetic field produced is weak and limited to the shaded pole design.
Q3. Can the rotation direction be reversed?
Ans: No, reversing the direction is not possible without modifying the pole structure or shading coil position.
Q4. What type of rotor is used?
Ans: A squirrel cage rotor is used in shaded pole induction motors.
Q5. Where are shaded pole motors commonly used?
Ans: In low-power devices like fans, blowers, toys, and appliances where simplicity and low cost are priorities.
Conclusion
Shaded pole induction motors are ideal for small, low-power applications where simplicity and cost-effectiveness are essential. Despite their low efficiency and torque, their rugged construction and maintenance-free operation make them a popular choice for domestic and commercial appliances.