Lecture Notes EEE 360 TOPIC 4 Synchronous Machine - Lecture 13 docx

06/29/14 360 Topic 6. Synchr.
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Lecture Notes
EEE 360
George G. Karady
TOPIC 4
Synchronous Machine
Read Chapter: 7.1, 7.2, 7.4, 7.6, 5.6, 5.7
06/29/14 360 Topic 6. Synchr.
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Lecture 13
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Animation 1
Voltage induced in
a rotating loop
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Energy Conversion
Concept:
•
Generators convert mechanical energy to electric energy.
•

Motors convert electric energy to mechanical energy.
•
The construction of motors and generators are similar.
•
Every generator can operate as a motor and vice versa.
•
The energy or power balance is :
–
Generator: Mechanical power = electric power +
losses
–
Motor: Electric Power = Mechanical Power +
losses.
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Energy Conversion
Voltage generation
(Generator)
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A wire loop is rotated in a
magnetic field.
–
N is the number of turns
in the loop
–
L is the length of the loop
–
D is the width of the loop

–
B is the magnetic flux
density
–
n is the number of turns
per seconds
D
B
L
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Energy Conversion
Voltage generation
(Generator)
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A wire loop is rotated in a
magnetic field.
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The magnetic flux through
the loop changes by the
position
( ) ( )
tcosLDBt ω=Φ
n
π=ω
2
cos ωt
D

B
L
2
1
B
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Energy Conversion
Voltage generation
(Generator)
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Position 1 all flux links with
the loop
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Position 2 the flux linkage
reduced
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The change of flux linkage
induces a voltage in the loop
( )
( ) ( )
[ ]
( )
tsinLDBN
dt
tcosd
LDBN
dt

td
NtV ωω=
ω
==
Φ
cos ωt
2
1
B
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Energy Conversion
Voltage generation
(Generator)
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The induced voltage is an
ac voltage
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The voltage is sinusoidal
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The rms value of the
induced voltage loop is:
2
ω
=
LDBN
V
rms

cos ωt
2
1
B
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View the animation of
voltage generation
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SYNCHRONOUS MACHINES
Round Rotor Machine
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The stator is a ring
shaped laminated iron-
core with slots.
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Three phase windings
are placed in the slots.
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Round solid iron rotor
with slots.
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A single winding is
placed in the slots. Dc
current is supplied
through slip rings.
Concept (two poles)
N

S
A
-
B
+
A
+
C
+
C
-
B
-
A
B
C
Stator with
laminated iron-core
Slots with
winding
Rotor with dc
winding
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SYNCHRONOUS MACHINES
Salient Rotor Machine
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The stator has a laminated iron-

core with slots and three phase
windings placed in the slots.
•
The rotor has salient poles
excited by dc current.
•
DC current is supplied to the
rotor through slip-rings and
brushes.
•
The number of poles varies
between 2 - 128.
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Concept (two poles)
N
S
A
+
B
+
C
+
B
-
A
-
C
-
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SYNCHRONOUS MACHINES
Stator
Rotor
Connections
Bearing
Stator winding
Rotor winding
Housing ,cooling ducts
Shaft
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SYNCHRONOUS MACHINES
Construction
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The picture shows the laminated
iron core and the slots (empty
and with winding).
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The winding consists of copper
bars insulated with mica and
epoxy resin.
•
The conductors are secured by
steel wedges.
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In large machines, the stator is

liquid cooled.
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The iron core is supported by a
steel housing.
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Construction
empty slots
insulated
winding
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SYNCHRONOUS
MACHINES
Stator
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Laminated iron core
with slots
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Steel Housing
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SYNCHRONOUS
MACHINES
Stator details
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Coils are placed in slots

• Coil end windings are
bent to form the
armature winding.
Slots
Coil
End winding
Iron core
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SYNCHRONOUS MACHINES
Round rotor
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The round rotor is used
for large high speed
(3600rpm) machines.
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A forged iron core (not
laminated,DC) is
installed on the shaft.
•
Slots are milled in the
iron and insulated
copper bars are placed
in the slots.
•
The slots are closed by
wedges and re-enforced
with steel rings.

Round rotor
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SYNCHRONOUS MACHINES
Rotor Details
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SYNCHRONOUS MACHINES
Round rotor

Steel ring
DC current terminals
Wedges
Shaft
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SYNCHRONOUS
MACHINES
Salient pole rotor construction
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The poles are bolted to the shaft.
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Each pole has a DC winding.
•

The DC winding is connected to the slip-rings (not shown).
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A DC source supplies the winding with DC through brushes
pressed into the slip ring.
•
A fan is installed on the shaft to assure air circulation and
effective cooling.
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SYNCHRONOUS MACHINES
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SYNCHRONOUS
MACHINES
Construction
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Low speed, large hydro-
generators may have more
than one hundred poles.
•
These generators are
frequently mounted vertically.
•
The picture shows a large,
horizontally arranged
machine.

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Animation 2
Generator
Operation
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Test 2
Transformer
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Lecture 14
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SYNCHRONOUS MACHINES
Operation concept
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The rotor is supplied by DC current I
f

that generates a DC flux Φ
f

.
•
The rotor is driven by a turbine with
a constant speed of n
s
.
•
The rotating field flux induces a
voltage in the stator winding.
•
The frequency of the induced
voltage depends upon the speed.
Operation (two poles)
N
S
A
+
B
+
C
+
B
-
A
-
C
-
Flux Φ
f
n

s
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SYNCHRONOUS
MACHINES
Operation concept
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The frequency - speed relation is f = (p / 2) n
s

= p n
s
/ 2
p is the number of poles.
•
Typical rotor speeds are 3600 rpm for 2-pole, 1800 rpm for 4 pole and
450 rpm for 16 poles.
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The rms. value of the induced voltages are:
•
where:
k
w
= 0.85-0.95 is the winding factor.
degOi
rmsan
eEE =
degi

rmsbn
eEE
120−
=
degi
rmscn
eEE
240−
=
wfa
faw
rms
kNf.
Nk
E Φ
Φ
444
2
=
ω
=