INDUCTION MOTORS. SUBMITTED BY: Ms. APOORVA KANTHWAL ASST. PROFESSOR-EEE. Induction Motor (Asynchronous Motor). ELECTRICAL MACHINES. Contents. Overview of Three-Phase Induction Motor Construction Principle of Operation Equivalent Circuit Power Flow, Losses and Efficiency
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INDUCTION MOTORS
SUBMITTED BY:
Ms. APOORVA KANTHWAL
ASST. PROFESSOR-EEE
Induction Motor(Asynchronous Motor)
ELECTRICAL MACHINES
General aspects
Squirrel Cage Rotor
MZS FKEE, UMP
Short circuits all
rotor bars.
/rotor winding
Wound Rotor
Squirrel-Cage Rotor
MZS FKEE, UMP
Stator
Rotor
Air gap
f = the frequency of supply
RMF(Rotating Magnetic Field)
a
Fc
b’
1.5
c’
Fa
F
t = t0= t4
F
1
Fa
c
Fc
b
0.5
Fb
a’
0
Fb
-0.5
t = t0= t4
-1
-1.5
-93
10
113
216
F
Space angle () in degrees
Fb
Fc
a
Fb
b’
a
a
c’
b’
b’
c’
c’
Fa
c
b
c
c
F
b
b
a’
Fc
Fc
a’
a’
Fb
t = t2
t = t3
t = t1
F
AC Machine Stator
MMF Due to ‘a’ phase current
1
Axis of phase a
0.8
t0
0.6
t01
0.4
0.2
Fa
a’
a
0
a’
t12
-0.2
-0.4
-0.6
t2
-0.8
-1
-90
-40
10
60
110
160
210
260
Space angle (theta) in degrees
Currents in different phases of AC Machine
t01
t12
Amp
t1
t2
t3
t4
t0
time
1 Cycle
Slip Ring Rotor
nr = mechanical speed of rotor (rpm)
MZS FKEE, UMP
f = supply frequency
f
f
(The rotor will not rotate)
f
fr
(Under normal operating conditions, the rotor winding is shorted. The slip is s)
Keep the rotor current same:
MZS FKEE, UMP
MZS FKEE, UMP
I
1
Note: can be separated into 2 PARTS
MZS FKEE, UMP
Is1
Im1
IR1
Zs
Vs1
Zm
ZR
Is=I1 , IR=I2
(s=stator, R=rotor)
Is1
Im1
IR1
Zs
Vs1
Zm
ZR
Note : 1hp =746Watt
Pin (Motor)
Pdeveloped
Pmechanical
Pconverted
(Pm)
Pin (Rotor)
Pout, Po
Pair Gap (Pag)
Pin (Stator)
Pstator copper loss, (Pscu)
Protor copper loss (Prcu)
Pwindage, friction, etc (P - Given)
Pcore loss
(Pc)
Ratio makes the analysis simpler to find the value of the particular power if we have
another particular power. For example:
Tmax
Tm
Tst
s=1
ns
smax
smax is the slip for Tmax to occur
Hence, Plot Tmvs s
T
R1<R2<R3
nr1< nr2< nr3
R1
R2
R3
T
n
nr3
nr2
nr1
ns~nNL
T
V1
V decreasing
V2
V1>V2 >V3
nr1> nr2 > nr3
V3
T
n
nr3
nr2
nr1
ns~nNL
f decreasing
T
T
n
nr3
nr2
nr1
nNL1
nNL3
nNL2