Transcript Induction Machine

Induction Machine
Induction Machine
(N. Tesla 1888)
Principle of operation
 Construction
 Characteristics:

 slip
 rotor
current
 power
 torque
Classification
 Control

Principle of operation
o
squirrel-cage rotor
o
o
Three-Phase Supply Voltage
A
B
C
N
60 120
S
A
120
C
B
Resultant Stator Flux
Rotating Magnetic Flux
A
A
C
B
0
C
B
60
It’s electromagnetic
induction !!!
Induction Motor

electromagnetic induction
 rotating
magnetic flux induces an alternating
 current in the rotor

motor action
 interaction
of the induced rotor-current with
 the rotating field produces motor torque
Direction of Rotation
N
i
The rotor follows the rotating magnetic flux !
How to change the direction of
rotation?
change the direction of rotation of the
rotating magnetic flux
 change the phase sequence of the applied
voltage

Synchronous Speed
speed of the rotating magnetic flux
 ns = fs / (P/2)

Slip Speed n, Slip s

n = ns - nr

s = ( ns - n r ) / n s

if nr then n and s

for nr = ns
s=0
fr : frequency of the induced
voltage in the rotor
 fr = P n / 120
n = ns -nr
Rotor Current
1 -------- slip ---.2 - 0
0 ------ speed ---- 100%
Rotor Current Phasor
}
Ir cos (theta): horizontal component
s = .05
s = .2
SGAP = EBRIr (cos 0 + j sin 0)
s=1
Interpreting the Circle Diagram
s = .05
Assume s = .05; If Tload
s = .2
nr
s
Ir
Ir cos0
sufficient to carry the load
s=1
Power-Flow Diagram
Pgap
Pmech
Pin
Pshaft
Pscl
Pcore
Prcl
Pf,w Pstray
Mechanical Power vs Torque
Pmech = TD
nr / 5252
(hp)
shaft speed r/min
developed torque lb-ft
mechanical power developed in rotor hp
TD Torque
Torque vs Speed
o
o
breakdown
o rated value
locked rotor
1
slip
0
Torque-Speed Characteristics
2
T
D
T
D
C
A-B
Speed

2112
. Rr E BR
2
s nr [( Rr / s ) 
X
2
BR
]
Can slip at maximum torque be
changed?
Elevator
Tmax
Speed
sT max 
R
R (X  X
2
2
1
1
2
)
2
Induction Generator
Induction
Motor
Turbine
Increasing rotor speed above ns will reverse direction of PGAP
==> power is transferred in reverse direction, from rotor to stator
Induction Motor Starting
Autotransformer Starting
 Y-Delta Starting


Series Impedance

Solid State Starting
Breaking (rotating rotor induces
currents to be dissipated in stator circuit)
DC Injection
 Capacitor Breaking

Single-Phase Induction Motor
There is no rotating magnetic flux
 How to produce needed rotating flux?
 Quadrature Field

Quadrature-Axis Flux (flux
induced by rotor current)
Stator or direct-axis flux
Quadrature-axis or
rotor flux
Phase Splitting
Single
phase
Phase
Splitter
Split-Phase Motors
Resistance-Start Split-Phase Motors
 Capacitor-Start Split-Phase Motors
