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7/27/2019 Chapter 4 Ee 342 Ac Fundamentals
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Chapter 4 (P#230)
AC MachineryFundamentals
Pole
DC excitation
windingFan
Slip
rings
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AC Generator (Field Fix Armature Rotating)
Will it work asAC Generatorif theArmature is
fixed and Field is rotating ?
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4.1 A simple Loop in a uniform Magnetic Field (230)
(Voltage Induced in a simple rotating Loop (Page 231 ))
eind = ZBVLsin single conductor (Z=1)
eind = 2 BVLsin loop (2 conductors Z=2)
eind = maxsin t [4-11 ]Z
S
The voltage generated in the loop is a sinusoidal whose
magnitude is equal to the product of the flux inside the machine
and the speed rotating of the machine
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4.1 A simple Loop in a uniform Magnetic Field (230)
(Torque Induced in a current-carrying Loop (Page 234 ))
F = ZBILsin single conductor (Z=1)
F = 2 BILsin loop (2 conductors Z=2)
ind = k Bloopx BS [4-20 ]
The torque induced in the loop is proportional to the strength of
the loops magnetic field, the strength of the external magnetic
field, and the sine of the angle between them.
r
N
S
F
F
X
X
Bloop
BS
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4.2 (page 238) Rotating Magnetic Field
(Page 242 - The relationship between Electric Frequency and the
speed of Magnetic Field Rotation)
).(Pn
f me
344
120
nm = speed of magnetic field in rev/min
fe = electric frequency in Hz (Hertz cycle/sec)
P = Number of poles (North south are counted as 2-poles)
How the stator magnetic field be made to rotate?
The fundamental principle of ac machine operation is that:
IF a 3-phase set of currents, each of equal magnitude and
differing in phase by 1200, flows in a 3-phase winding, then it willproduce a rotating magnetic field of constant magnitude (1.5
times the peak value).
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The three phase winding consists of three separate windings
spaced 1200 electrical apart around the surface of the machine
(Page 244)Reversing the Direction of Magnetic Field Rotation
If the current in any two of the three coils is swapped, the direction
of magnetic fields rotation will be reversed. This means that it is
possible to reverse the direction of rotation of an ac motor just byswitching the connections on any two of three coils.
http://en.wikipedia.org/wiki/File:3-phase_flow.gif7/27/2019 Chapter 4 Ee 342 Ac Fundamentals
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Page 241 Proof of the Rotating Magnetic Field
Next Few Slides Will Demonstrate The
Revolving Magnetic Field in The Stator Windings
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ALTERNATOR (AC Generator or Synchronous Generators)
The elementary 3-phase 2-pole synchronous generator has a
stator equipped with 3 coils displaced 120o from each other;
although shown as concentrated, they actually are distributed.
When the rotor is excited with dc and rotated, the resultant
field will also rotate so that sinusoidal voltages are generated
in the 3 stator phases, displaced 120o in time and having a
frequency directly related to rotor speed.
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Page 241 Proof of the Rotating Magnetic Field
A -C B -A C
0o 360o
-C
-B
CB
A
-A
-B
Stator winding
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Phase A
magnetic axis
corresponding coil
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Phase Bmagnetic axis
corresponding coil
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Phase C
magnetic axis
corresponding coil
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7/27/2019 Chapter 4 Ee 342 Ac Fundamentals
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in
out
P
P)(Efficiency
in
lossesin
P
PP
lossesout
out
PP
P
in
losses
P
P 1
1. Electrical Losses or Copper Losses (I2R)
2. Core Losses=Hysteresis+Eddy Current Losses (Proportional to Speed & )
3. Mechanical Losses (Proportional to speed)
4. Stray Load Losses 1% of the Full Load rated Capacity (100 W 1 W)
Armature (Stator) Losses Field (Rotor) Losses ( Fixed IF )
AAA RIPlossArmature23 FFF RIP)Rotor(lossField
2
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Pout=VIAcos=3VLILcos
Stray
Losses
1% of Rating
Mechanical
Losses
= Friction
+ WindageLosses
Core
Losses
= EddyCurrent
+ HystersisLosses
I2R Losses= Armature
+ Field
Losses
Mechanical
in= appm
Pout = Pin - Losses
indm
Pconv
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StrayLosses
1% of Rating
Mechanical
Losses
= Friction
+ Windage
Losses
Core
Losses
= EddyCurrent
+ Hystersis
Losses
I2R Losses
= Armature
+ FieldLosses
Pout=VIAcos=3 VLILcos
Pout = Pin - Losses
indm
Pconv
Mechanical
Pout= indm
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AC Generator are compared by their
VOLTAGE
POWER RATINGS
EFFCIENCIES
VOLTAGE REGULATIONS
AC Motors are compared by their:
SPEED
POWER RATINGS
EFFCIENCIES
SPEED REGULATIONS
FL
FLNLgulationReSpeed
FL
FLNL
V
VVgulationReVoltage
Assume the Motors are run
from a constant source
(VT), unless voltage change
is specified
Assume the Generators are are
run from a constant Speed
source called Prime Mover,
unless speed change is specified
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END OF CHAPTER 4
NEXT CHAPTER 5
Synchronous Generators
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http://www.ece.umn.edu/users/riaz/animations/spacevectors.html
http://www.coolmagnetman.com/magacmot.htm
M t G t
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Motor Generator
RA
EA
RA
EA
IA= IL
+
-
+
-
+
-
+
-
IF
VTRA
EA
RA
EA
IA= IL
+
-
+
-
IF
LVT
Separately
&
shunt
M/R & G/R
)R+R(IE=V SAAAT
RA
EA
RA
EA
+
-
+
-
IA= IL=IF
VTVT
RA
EA
RA
EA
IA= IL=IF
RL
2
AI'K=
EA=K
VT=EAIARA
EA=K
T=KIA
7/27/2019 Chapter 4 Ee 342 Ac Fundamentals
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RA
EA
RA
EA
RA
EA
RA
EA
RA
EA
RA
+-
+
-
+
-
RA
EA
RA
EA
RA
EA
IA= IL
+
-
+
-
+
-
+
-
IF
T
IAIL
http://en.wikipedia.org/wiki/File:3-phase_flow.gif