ac machines
DESCRIPTION
AC Machines. 6077SA NUE 046. 3 Phase Synchronous Alternators. Alternators. 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 - PowerPoint PPT PresentationTRANSCRIPT
6077SANUE 046
3 PhaseSynchronous Alternators
Alternators
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
At the end of this section you will be able to:
Types
Governed By:• Load Current Requirements
• Single or Three Phase
• Prime Mover Speed
Prime MoverDetermines Speed of Alternator
• Windmill
• Diesel Motor
• Water turbine
Slow Speed High Speed
• Steam turbine
Number of PolesSpeed Determines Number of Poles
OR
50 Hz Required
p
fn120
n
fp120
Number of Poles
750 RPM = 8 Poles
n
fp120
1500 RPM = 4 Poles
3000 RPM = 2 Poles
375 RPM = 16 Poles
Number of PolesDetermines Shape of Alternator
16 Poles•Large Diameter
• Short length
Salient Pole
Number of PolesDetermines Shape of Alternator
2 Poles •Small Diameter
• LongCylindrical
Generated VoltageDependant on • Flux density
• Flux strength
• Speed of rotation
• Number of turns per pole
• Length of pole
• Area of pole face
Generated VoltagefNE m 44.4
Φm
f
N
= Maximum flux
= Frequency
= Number of poles
Generated Voltage
dpm kfNkE 44.4Φm
f
N
kp
kd
= Maximum flux
= Frequency
= Number of poles
= Pitch factor
=Distribution or Breadth factor
Voltage RegulationVoltage Regulation
EI
Voltage Drop Due to R
Voltage Drop Due to XL
V
• Resistance• Inductance
Coils have both
Line Current
Ter
min
al V
olt
age Vg
Unity PF
Voltage RegulationVoltage Regulation
Voltage RegulationVoltage Regulation
EI V
Lagging PF of 45
V less than E
Line Current
Ter
min
al V
olt
age Vg
Unity PF
Lagging PF
Voltage RegulationVoltage Regulation
Voltage RegulationVoltage Regulation
EI
V
Leading PF of 45
V More than than E
Line Current
Ter
min
al V
olt
age Vg
Unity PF
Lagging PF
Leading PF
Voltage RegulationVoltage Regulation
Voltage RegulationVoltage Regulation
100 x VNo Load – V Full Load
VFull Load
R% =
If PF = Unity
100 x I x (R x cos + XL x sin)
VFull Load
R% =
ExcitationWith Brushes
DC Generator Brushes Rotor Stator
Excitation
Sensor & Regulator
Rotating ComponentsWithout Brushes
Exc
itat
ion
Sta
tor
Synchronising Generators
Synchronized when all lamps dark
Synchronising Generators
Synchronized when1 lamp dark
2 lamps light
END