Shaded Pole Induction Motor is a type of single-phase motor consists of a stator and a cage-type rotor. It is a self-starting motor. It is also called as Shaded Pole Motor.
Definition
Shaded pole motor is a salient-pole, split phase type, squirrel cage rotor single phase induction motor provided with one or more auxiliary short-circuited stator winding is placed in magnetic position from the main winding.
The fig. 1 shows the basic construction of two poles shaded pole induction motor. It is made of stator and cage-rotor. The stator consists of salient poles or projected poles (called mainpoles). The supply winding forms main winding on the mainpoles. The poles are divided into two unequal halves. The smaller portion (a) carries the copper band and is called a shaded portion of the pole. On the smaller part, a single turn copper ring is fitted. This copper ring is known as a shading coil. The mainpole part on which this shading coil is fitted is known as shading pole.
Shaded Pole Induction Motor Working
When single-phase supply is applied, an alternating flux is generated in the core. A fraction of this flux links with the shaded coil. The variation in the flux induces the voltage in the coil. Since this shaded portion is short-circuited, the circulating current is produced in it in such a direction to oppose the main flux.
The circulating current develops the flux in the ring which opposes the main core 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 flux in shaded pole lags behind the flux in the unshaded pole. The main motor flux and the shaded ring flux are also having a space displacement less than 90°.
Since there are space and time displacement between the two fluxes, the rotating magnetic field is produced. Due to this rotating field, a torque is developed on the cage rotor. The direction of rotating magnetic field and hence flux is from unshaded portion to shaded portion of the mainpole.
In a shaded-pole motor, the reversal of the direction of rotation is not possible.
The reversal of the direction of rotation, where desired, can be achieved by providing two shading coils, one on each end of every pole, and by open-circuiting one set of shading coils and by short-circuiting the other set.
Shaded Pole Induction Motor Advantages
1. They have Low cost.
2. Self-starting
3. Construction is simple and robust because there is no centrifugal switch.
4. Reliable
Shaded Pole Induction Motor Disadvantages
1. Starting torque is very low.
2. Power factor is low.
3. Losses in Shaded Pole Induction Motor are high.
4. Hence, efficiency is very low.
5. The speed reversal is also difficult and expensive as it requires another set of copper rings.
Shaded Pole Induction Motor Applications
Shaded Pole Induction Motor is used to drive the devices which require low starting torque.
1. They are suitable for small devices like relays and fans.
2. Record players, tape recorders, projectors, photocopying machines.
3. Used in air conditioning and refrigeration equipment and cooling fans.
4. Used in exhaust fans, hair dryers and also in table fans.
5. Used for starting electronic clocks and single-phase synchronous timing motors.
