Definition: The shaded pole induction motor is simply a self-starting single-phase induction motor whose one of the poles is shaded by the copper ring. The copper ring is also called the shaded ring. This copper ring acts as a secondary winding for the motor. The shaded pole motor rotates only in one particular direction, and the reverse movement of the motor is not possible.
Why the Shaded Pole Induction Motor designs for low power rating?
The power losses are very high in the shaded pole induction motor, and the power factor of the motor is low. The starting torque induces in the induction motor is also very low. Because of the following reasons the motor has poor efficiency. Thus, their designs are kept small, and the motor has low power ratings.
Construction of Shaded Pole Induction Motor
The shaded pole motor may have two or four poles. Here in this article, we use the two-pole motor for the sake of simplicity. The speed of the motor is inversely proportional to the number of poles used in the motor.
Stator – The stator of the shaded pole motor has a salient pole. The salient pole means the poles of the magnet are projected towards the armature of the motor. Each pole of the motor is excited by its exciting coil. The copper rings shade the loops. The loops are known as the shading coil.
The poles of the motor are laminated. Lamination means multiple layers of material are used for making the poles. So, that the strength of the pole increases.
The slot is constructed at some distance apart from the edge of the poles. The short-circuited copper coil is placed in this slot. The part which is covered with the copper ring is called the shaded part and which is not covered by the rings is called the unshaded part.
Rotor – The shaded pole motor uses the squirrel cage rotor. The bars of the rotor are skewed at an angle of 60º. The skew can be done for obtaining a better starting torque.
The construction of the motor is very simple because it does not contain any commutator, brushes, collector rings, etc., or any other part. The shaded pole induction motor does not have any centrifugal switch. Thus, the chances of failure of the motor are less.
The centrifugal switch is the type of electrical switch that starts operating by using the centrifugal force, generated by the rotating shaft. It is also used for controlling the speed of the shaft.
Shaded Pole Induction Motor Working
When the supply is connected to the windings of the rotor, the alternating flux induces in the core of the rotor. The small portion of the flux link with the shaded coil of the motor because it is short-circuited. The variation in the flux induces the voltage inside the ring because of which the circulating current induces in it.
The circulating current develops the flux in the ring which opposes the main flux of the motor. The flux induces in the shaded portion of the motor, i.e., a, and the unshaded portion of the motor, i.e., b have a phase difference. The main motor flux and the shaded ring flux are also having a space displacement by an angle of 90°.
The connection diagram of the Shaded Pole Motor is shown below:
As there is time and space displacement between the two fluxes, the rotating magnetic field induces in the coil. The rotating magnetic field develops the starting torque in the motor. The field rotates from the unshaded portion to the shaded portion of the motor.
Applications of the Shaded Pole Induction Motor
The various applications of the shaded poles motor are as follows:
- They are suitable for small devices like relays and fans because of their low cost and easy starting.
- Used in exhaust fans, hairdryers, and also table fans.
- Used in air conditioning and refrigeration equipment and cooling fans.
- Record players, tape recorders, projectors, photocopying machines.
- Used for starting electronic clocks and single-phase synchronous timing motors.
This type of motor is used to drive devices that require low starting torque.