1. Unit – V Single phase Induction motors and Special machines

2. Construction
Stator similar to three phase induction motor - starting or auxiliary winding in addition to main Winding on the stator – the two windings in space quadrature – Rotor squirrel cage . Largely used as fractional horse power motors in a variety of industrial and domestic applications.

3. Double-field Revolving Theory
The pulsating sinusoidally distributed MMF
in the air gap is divided into two
components rotating in opposite directions,
called Forward field and Backward field .
Each of these develops torque in
Opposite directions due to induction motor
action.

4. Equivalent Circuit Equivalent circuit has two components
One for forward field with slip S
Other for Backward field with slip (2-S)
The net torque is positive in the direction in
which the motor is started.
Solving the equivalent circuit for any slip S the performance of the motor can be determined.

5. No Load And Blocked Rotor Test
No load test : Rated voltage is applied to the main winding - input current and power are measured. Blocked rotor test : Reduced voltage applied to the main winding – rotor blocked (rated current not to be exceeded) – input current and power measured. Main winding resistance measured.

6. Starting Methods
Split phase method: (i) Resistance start motor (ii) Capacitor start motor (iii) Capacitor run motor and (iv) Capacitor start – capacitor run motor

7. Shaded Pole Motors
Stator has salient poles with exciting coil - Apart from that a portion of each pole is wrapped by a short circuited copper strap forming a closed loop known as shading coil - rotor is of squirrel cage type.

8. Reluctance Motors The stator produces rotating magnetic field.
Rotor is non cylindrical – The reluctance of the magnetic path offered by the rotor to the rotating field is a function of space angle.
Rotor has a tendency to align itself in the minimum reluctance position
Motor made self starting by induction principle by providing short circuit copper bars in the projecting parts of the rotor.

9. Repulsion Motors
The repulsion motor are similar to series motor i.e. high starting torque and high speeds at light loads. The stator carries a distributed winding like main winding of ordinary single-phase induction motor. The rotor is similar to d.c.motor armature.

10. Hysteresis Motors
When the rotor of an induction motor is built up of a group of a specially hardened steel rings instead of usual thin silicon steel laminations, the effect of hysteresis is magnified. As a result, the rotor will operate at synchronous speed because the hysteresis property of the rotor steel strongly opposes any change in the magnetic polarities once they are established.

11. Stepper Motor
A stepper motor is an incremental motion machine i.e. the motor which turns in discrete movement called steps.
The stepper motor is a special type of synchronous motor which is designed to rotate through a specific number of degrees for each electrical pulse received by its control unit.

12. AC Series Motor
Field and armature windings are connected in series. when an alternating EMF is applied to the motor, since the field flux and armature current reverses simultaneously every half cycle, the direction of the torque remains unchanged. The torque is pulsating, but the average value is equal to that of d.c.motor.