lectut een 112 ppt induction machines

8/17/2019 Lectut EEN 112 Ppt Induction Machines

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Induction Machines


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Construction

Squirrel Cage

Slip-ring

Or

Wound-rotor


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Stator

Rotor


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Revolving magnetic filed


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• Emf is induced in rotor conductors (of same frequency)

of rotor conductors & revolving magnetic flux.

• Since rotor bars forms closed circuit, rotor currents flow proportional to the relative speed and direction is such

the very cause which produces them (according to en

• So, the rotor starts rotating and tries to catch up with th

• #ut never succeeds, otherwise no relative speed, no rot

thus no rotor motion.

• So, the rotor speed is always slightly less than the sync

the rotating magnetic field.


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$enerally

+speed of rotating magnetic field, ()

rotor speed , ( )

relative speed of rotor w.r.t. rotating magnetic field %

hence frequency of the emf induced in the r

s

s

f N

P

N N N

N

=

<

∴

+

+

+

otor conductor

( ) ( )

+ +

( )

(+)

where slip (&

s s s

s

s

s

s

s

N N P N N N P f

N

N N f f

N

f sf

N N s

N

− −= = ×

−=

=

−= )

from (&),

or ( ) (-)

s s

s

sN N N

N s N

= −

= −


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+

he slip frequency rotor currents in the rotor winding produce their own magneti

rotating in the same direction at the speed (w.r.t. to rotor)

( )+

+ + (

s

s s

N N f

N f sf N N P P P

−

= = = − +)

Since the rotor is rotating at the speed / and its own flux is rotating at a speed (/

w.r.t to itself. 0ence net speed of the rotor field as seen from the stator (or ground

s

s

f N N PN

= −

s % / 1 (/ '/) % /

0ence the rotor field rotates with the same speed as the stator field i.e. the rotor f

stationary w.r.t. to stator field.he two synchronously rotatin

s

g magnetic fields sup

other and give rise to the actually existing rotating field corresponding with the m

of the stator winding.


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Starting Torque

E2

2 2 3242

Rotor side

+ +

+ +

+ ++ +

+ + + +

+ + + +

++

+ +

+ +

5s in case 67 motors orque

in case 4nduction motors cos

% cos

where & cos

.

a

s

T I

T I

T k I

E R I

R X R X

E T kE

R X

α ϕ

α φ ϕ

φ ϕ

ϕ = =+ +

=+

+

+ + +

+ ++ ++ ++ +

+

.

(as )

here

+ s

R E Rk

R X R X

E

k

N

φ α

π

=++

=

+

+

8ith applied voltage co

and thus E w

9

:or maximum starting t

sT k R

R

φ

=

=

(max) sT =


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Torque under Running Conditions

sE2

2 2 s3242

Rotor side

+ +

+ +

+ ++ +

+ + + +

+ + + +

+ ++

+ + + +

+ + + +

+

cos

% cos

where & cos( ) ( )

. .( ) ( )

T I

T k I

sE R I

R sX R sX

sE RT kE

R sX R sX

sE T k

α φ ϕ

φ ϕ

ϕ = =

+ +=

+ +

=+

+

+ +

+ +( )

R

R sX +

+ +

+++

+(max)

+ ++

+

:or maximum torque

so the slip at which maximum trouq

.

dT

ds

R sX

R E

X T k

R R

X

=

=

=

+

+

+(max)

+

+

+(max)

+

+

% .

+ + s

E T k

X

E T

N X π

=


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Complete Torque-Slip Characteristics


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14/24

Induction Motor as Generalized Transformer i


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Induction Motor as Generalized Transformer quivalent

!hasor "iagram

!arameter Calculation

#o-load test $loc%ed Rotor test

Stator

Rotor

V

I

P

sc

sc

sc

V

I

P


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Single !hase Induction Moto


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No revolving feld – only pulsating feld

No self-starting

Due to single winding:

Revolving &ield Theor'

Construction

Slip of the rotor with forward rotating flux


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Slip of the rotor with forward rotating flux

Slip of the rotor with bac


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(

R1 X1I1

E

Eb

#o-)oad Test *s+, $loc%ed-Rotor Test *s+

quivalent Circuit of Single !hase Induction Motor

!" I!" #!

%&pen'

!

I!


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/0 Split 1 !hase Motor


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$0 Capacitor-Start Motor


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C0 !ermanent Split Capacitor Motor


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"0 Capacitor-Start Capacitor-Run Motor

Sh d d ! l I d ti M t


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0 Shaded !ole Induction Motors

lectut een 112 ppt induction machines

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