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THREE-PHASE CAGE ROTOR INDUCTION MOTORS

Resource 2

Three-Phase AC machines

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Aims

1.To understand the rinci!e o" the oeration o" the motor

2.To descri#e the construction o" a ca$e rotor induction commercia!

motor

3.To understand the "actors that a""ect the er"ormance o" the

motor

Three-Phase AC MachinesResource 2

Three-phase Cage Rotor

Induction Motors

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Objectives

At the end o" this !esson %ou shou!d #e a#!e to&

' Descri#e the rinci!e o" the rotatin$ ma$netic "ie!d

' Descri#e the rinci!e o" rotor ca$e induction

' Descri#e the construction o" a commercia! stator

' Descri#e the construction o" a commercia! ca$e rotor' E(!ain and ca!cu!ate s%nchronous seed

' E(!ain and ca!cu!ate "ractiona! s!i

' Descri#e the e""ect uon the er"ormance o" the motor #%

connectin$ the stator in star and de!ta

' Per"ormance sim!e ca!cu!ations in)o!)in$ e!ectrica! and mechanica!

arameters that descri#e the er"ormance o" the motor

' Descri#e the er"ormance cur)e "or a ca$e rotor induction motor

Three-Phase AC MachinesResource 2

Three-phase Cage Rotor

Induction Motors

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Iron Po!e

Pieces

Phase connections

A

A

B

B

C

C

IronStator

Rin$

PhaseCoi!s

Sim!e stator made o" * o!e airs o" coi!s around iron o!e ieces

'Current enters coi!

Aand !ea)es coi!s A

'Ma$netic "!u( set

u in coi!s +ith

North Po!e at the

#ottom and South

Po!e at the to

Three-Phase AC MachinesResource 2

Three-phase Cage Rotor

Induction Motors

1. Principe o! Operation

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1. Principe o! Operation

Chan$in$ +hich coi!s are ener$ised a!ters direction o" ma$netic "!u(

AA, ener$ised CC, ener$ised , ener$ised

Three-Phase AC MachinesResource 2

Three-phase Cage Rotor

Induction Motors

N

S

C

,

C,

A

A,

N

SN

S

C

,

C,

A

A,

C

,

C,

A

A,

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Ener$isin$ t+o sets o" coi!s to$ether in se.uence

Comass sett!es ha!" +a% #et+een o!es

Three-Phase AC MachinesResource 2

Three-phase Cage Rotor

Induction Motors

1. Principe o! Operation

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1. Principe o! Operation

Se.uence roduces one com!ete rotation o" the ma$netic "ie!d

/0 CC, 1 ,

20 AA, 1 ,

*0 AA, 1 C,C

0 , 1 C,C

30 , 1 A,A

40 CC, 1 A,A

50 CC, 1 ,

Three-Phase AC MachinesResource 2

Three-phase Cage Rotor

Induction Motors

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1. Principe o! Operation

Three-Phase su!% ro)ides the correct se.uence "or stator coi!s

Three-Phase AC MachinesResource 2

Three-phase Cage Rotor

Induction Motors

/0 CC, 1 ,

20 AA, 1 ,

*0 AA, 1 C,C

0 , 1 C,C

30 , 1 A,A

40 CC, 1 A,A

50 CC, 1 ,

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Three-Phase AC MachinesResource 2

Three-phase Cage Rotor

Induction Motors

1. Principe o! Operation

Three-Phase su!% ro)ides the correct se.uence "or stator coi!s

/0 CC, 1 ,

20 AA, 1 ,

*0 AA, 1 C,C

0 , 1 C,C

30 , 1 A,A

40 CC, 1 A,A

50 CC, 1 ,

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Rotor ca$e added in the centre o" the stator "ie!d

1. Principe o! Operation

Ca$e conductors

Ca$e rotor

Coer end rin$

Three-Phase AC MachinesResource 2

Three-phase Cage Rotor

Induction Motors

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As ma$netic "ie!d rotates6 ca$e conductors cut !ines o" ma$netic "!u(

1. Principe o! Operation

This induces currents in ca$e conductors

Induced currents roduce ma$netic "ie!d in rotor

Ma$netic "ie!d in rotor attracted to+ards rotatin$ stator "ie!d

Rotor turns in same direction as stator "ie!d #ut s!o+er

Three-Phase AC MachinesResource 2

Three-phase Cage Rotor

Induction Motors