1. AC Machines
6077SA
NUE 046

2. 3 Phase Synchronous Alternators

3. At the end of this section you will be able to:
Alternators
At the end of this section you will be able to:
Identify the basic components of a Alternator
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

4. Types Governed By: Load Current Requirements Single or Three Phase
Prime Mover Speed

5. Determines Speed of Alternator
Prime Mover
Determines Speed of Alternator
High Speed
Slow Speed
Windmill
Diesel Motor
Water turbine
Steam turbine

6. Speed Determines Number of Poles
50 Hz Required OR

7. Number of Poles 375 RPM = 16 Poles 750 RPM = 8 Poles 1500 RPM =

8. Determines Shape of Alternator
Number of Poles
Determines Shape of Alternator
16 Poles
Large Diameter
Short length
Salient Pole

9. Determines Shape of Alternator
Number of Poles
Determines Shape of Alternator
Small Diameter
Long
2 Poles
Cylindrical

10. Generated Voltage Dependant on Flux density Flux strength
Speed of rotation
Number of turns per pole
Length of pole
Area of pole face

11. Generated Voltage Φm f N
= Maximum flux
= Frequency
= Number of poles

12. Generated Voltage Φm f N kp kd = Maximum flux = Frequency
= Number of poles
= Pitch factor
=Distribution or Breadth factor

13. Voltage Regulation Resistance Inductance Coils have both I E V
Voltage Drop Due to R
Voltage Drop Due to XL

14. Voltage Regulation Vg
Unity PF
Terminal Voltage
Line Current

15. Voltage Regulation
V less than E I V E
Lagging PF of 45

16. Voltage Regulation Vg Terminal Voltage Unity PF Lagging PF
Line Current

17. Voltage Regulation
V More than than E I E V
Leading PF of 45

18. Voltage Regulation Leading PF Vg Terminal Voltage Unity PF Lagging PF
Line Current

19. Voltage Regulation If PF = Unity 100 x VNo Load – V Full Load R% =
100 x I x (R x cos + XL x sin)
R% =
VFull Load

20. Excitation
With Brushes
DC Generator
Brushes
Rotor
Stator

21. Excitation Without Brushes Rotating Components Excitation Stator
Sensor & Regulator

22. Synchronising Generators
Synchronized when all lamps dark

23. Synchronising Generators
Synchronized when
1 lamp dark
2 lamps light

24. END