1. AC Machines
6077 SA
NUE 046

2. 1 Phase Induction Motors
At the end of this section you will be able to:
Identify the basic components of a 1Ø induction motor
List the types of rotors used
Test motor windings for suitability to connect to the supply
Connect in both Clockwise and counter clockwise rotation
List the steps for dismantling it

3. Types Squirrel Cage Wound Rotor Split phase Capacitor start
Capacitor start Capacitor run
Permanent split phase capacitor run
Shaded Pole
Wound Rotor
Series universal
Repulsion

4. Construction

5. Construction Run or Main Windings Start or Auxiliary Windings
Low resistance
High XL
Set deeper in laminations to increase XL
Start or Auxiliary Windings
High resistance (thinner wire)
Low XL (fewer turns)
Set shallower in laminations to limit XL

6. Electrical Characteristics
IRef IS
Run Winding
Large phase Angle due to high Inductance IR
Start Winding
Phase Angle less, as Inductance is less than run winding

7. Split Phase Motor Construction Switch opens ≈ 70 – 80% full load speed
Low resistance
High XL
High resistance
Low XL

8. Split Phase Motor
Construction
Low resistance
High resistance

9. Split Phase Motor Capacitor Start Motor
Construction

10. Electrical Characteristics
Capacitor Start
Torque = K IR IS sinα
K = constant
α = Angle between IR and IS
IRef IS
Split Phase IR

11. Construction

12. Construction

13. Shaded Pole

14. Shaded Pole

15. Shaded Pole

16. Shaded Pole

17. Shaded Pole

18. Reluctance Motor 1Φ Synchronous Machine Low efficiency Low torque
Constant Speed
Fractional sizes

19. Reluctance Motor
Stator
Same as:
Split phase or
Capacitor Start Motor

20. Reluctance Motor Rotor Same as: Squirrel cage motor BUT, with
Uneven slots cut into laminations to form Salient poles
Uneven slots assist in starting
Rotor Slots generally ≠ Stator Slots

21. Reluctance Motor Starting Motor becomes Synchronous
As per induction motor with squirrel cage providing torque
Centrifugal switch operating as per normal(75%)
As motor is lightly loaded slip speed is small
Rotor salient poles become magnetised and lock with RMF
Motor becomes Synchronous

22. Reluctance Motor If rotor poles are a multiple of the stator poles
Motor will operate at sub-multiples of synchronous speed

23. Hysteresis Motor
Rotor
Outer section made up of hardened steel

24. Hysteresis Motor Rotor Outer section made up of hardened steel
This outer section supported on the shaft by a NON-MAGNETIC “Arbour”

25. Hysteresis Motor PROBLEM Rotor has a very high Hysteresis loss
The rotor tends to become magnetised
A synchronous motor is born
PROBLEM
Synchronous motors have ZERO START TOURQUE!
A Shaded pole stator is used

26. Universal Motor Not the same as a series DC Motor
Fields are laminated for AC current

27. Universal Motor

28. Universal Motor