Download AC Machines

6077SA
NUE 046
3 Phase
Synchronous Alternators
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
Types
Governed By:
• Load Current Requirements
• Single or Three Phase
• Prime Mover Speed
Prime Mover
Determines Speed of Alternator
Slow Speed
• Windmill
• Diesel Motor
• Water turbine
High Speed
• Steam turbine
Number of Poles
Speed Determines Number of Poles
50 Hz Required
120 f
n
p
OR
120 f
p
n
Number of Poles
120 f
p
n
375 RPM = 16 Poles
750 RPM = 8 Poles
1500 RPM = 4 Poles
3000 RPM = 2 Poles
Number of Poles
Determines Shape of Alternator
16 Poles
•Large Diameter
• Short length
Salient Pole
Number of Poles
Determines Shape of Alternator
2 Poles •Small Diameter
• Long
Cylindrical
Generated Voltage
Dependant on • Flux density
• Flux strength
• Speed of rotation
• Number of turns per pole
• Length of pole
• Area of pole face
Generated Voltage
E  4.44 m fN
Φm
f
N
= Maximum flux
= Frequency
= Number of poles
Generated Voltage
E  4.44 m fNk p k d
Φm
f
= Maximum flux
= Frequency
N
= Number of poles
kp
= Pitch factor
kd
=Distribution or Breadth factor
Voltage Regulation
Coils have both
•
•
Resistance
Inductance
I
E
V
Voltage Drop Due to R
Voltage Drop Due to XL
Voltage Regulation
Terminal Voltage
Vg
Unity PF
Line Current
Voltage Regulation
V less than E
I
V
Lagging PF of 45
E
Voltage Regulation
Terminal Voltage
Vg
Unity PF
Lagging PF
Line Current
Voltage Regulation
V More than than E
I
E
V
Leading PF of 45
Voltage Regulation
Leading PF
Terminal Voltage
Vg
Unity PF
Lagging PF
Line Current
Voltage Regulation
R% =
100 x VNo Load – V Full Load
VFull Load
If PF = Unity
R% =
100 x I x (R x cos + XL x sin)
VFull Load
Excitation
With Brushes
DC Generator
Brushes
Rotor
Stator
Excitation
Without Brushes
Excitation Stator
Rotating Components
Sensor & Regulator
Synchronising Generators
Synchronized when all lamps dark
Synchronising Generators
Synchronized when
1 lamp dark
2 lamps light
END