A Shaded Pole Induction Motor is a simple type of starting single phase induction motor. It consists of a starter and a cage-type rotor. The stator is made of salient poles. A copper ring is fitted on the smaller part of each pole. This section of the pole is known as Shaded Pole. The ring is usually a single turn coil and is known as Shading Coil.
The connection diagram of the Shaded Pole Motor is shown below.
An alternating flux is produced in the field core when the alternating current is supplied to the field winding. A portion of this flux links with the shading coil which behaves as a short circuit secondary of the transformer. Voltage is induced in the coil and, as a result, current circulates in the circuit.
The induced flux is produced by the current which is induced in the motor, and it opposes the main core flux. The flux generated in the shaded portion is produced by the shading coil is represented by (a) as shown in the above figure to lag behind the flux in the unshaded portion (b) of the pole. As there is a time and space displacement between the two fluxes, the conditions for setting up a rotating magnetic field is produced. This rotating flux develops the starting torque in the rotor.
The direction of the rotation of the flux is in a clockwise direction, i.e., from the unshaded portion to the shaded portion of the pole. In this motor, the reversal of the direction of rotation is not possible.
Shaded Pole pole motors are very cheap, and the starting torque developed by the motor is also very low. The losses are high, and the power factor of the motor is low. Hence, the efficiency of the motor is very low. Because of all these reasons, the shaded pole motors are built of the small size of the rating of 40 W or less.
Applications of the Shaded Pole Motor
This type of motor is used to drive the devices which require low starting torque. The various applications of the Shaded Poles Motor are as follows:-
- They are suitable for small devices like relays and fans because of its low cost and easy starting.
- Used in exhaust fans, hair dryers and also in 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.