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