Question

Explain the working principle of various types of single phase induction motor with neat circuit diagram.

Answer 1

The single phase induction motors are made self- starting by providing an additional flux by some additional means. Now depending upon these additional means the single phase induction motors are classified as:

1. Split phase induction motor.

2. Capacitor start inductor motor.

3. Capacitor start capacitor run induction motor (two value capacitor method).

4. Permanent split capacitor (PSC) motor .

5. Shaded pole induction motor.

1.Split Phase Induction Motor :  In addition to the main winding or running winding, the stator of single phase induction motor carries another winding called auxiliary winding or starting winding. A centrifugal switch is connected in series with auxiliary winding. The purpose of this switch is to disconnect the auxiliary winding from the main circuit when the motor attains a speed up to 75 to 80% of the synchronous speed.

We know that the running winding is inductive in nature. Our aim is to create the phase difference between the two winding and this is possible if the starting winding carries high resistance.

 

2.Capacitor Start IM and Capacitor Start Capacitor Run IM 

 The working principle and construction of Capacitor start inductor motors and capacitor start capacitor run induction motors are almost the same. We already know that single phase induction motor is not self-starting because the magnetic field produced is not rotating type. In order to produce rotating magnetic field there must be some phase difference.  In case of split phase induction motor we use resistance for creating phase difference but here we use capacitor for this purpose. We are familiar with this fact that the current flowing through the capacitor leads the voltage. So, in capacitor start inductor motor and capacitor start capacitor run induction motor 

3. Shaded Pole Single Phase Induction Motors

 

 The stator of the shaded pole single phase induction motor has salient or projected poles. These poles are shaded by copper band or ring which is inductive in nature. The poles are divided into two unequal halves. The smaller portion carries the copper band and is called as shaded portion of the pole.  When a single phase supply is given to the stator of shaded pole induction motor an alternating flux is produced. This change of flux induces emf in the shaded coil. Since this shaded portion is short circuited, the current is produced in it in such a direction to oppose the main flux. The flux in shaded pole lags behind the flux in the unshaded pole.  The phase difference between these two fluxes produces resultant rotating flux. We know that the stator winding current is alternating in nature and so is the flux produced by the stator current. In order to clearly understand the working of shaded pole induction motor consider three regions

1. When the flux changes its value from zero to nearly maximum positive value.

2. When the flux remains almost constant at its maximum value.

3. When the flux decreases from maximum positive value to zero.