Induction Motor Fundamentals.pdf

8/11/2019 Induction Motor Fundamentals.pdf

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Induction Motor Fundamentals


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UCFInduction Machine - Introduction

A machine with only armortisseur windings is called an

induction machine.

No DC field current is required to run the machine. Rotor

voltage is induced in the rotor windings rather than being

physically connected by wires.

Induction machine has the same physical stator as a

synchronous machine with a different rotor construction.

Induction machines can be operated as either motors and

generator. However, they are primarily used as induction motors.

Induction machines are by far the most common type of motor

used in industrial, commercial or residential settings.


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UCFIM Stator

Stator for a 2hp induction machine

http://www.ece.ualberta.ca/~knight/ee332/induction/basics/construction.html


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UCFIM Rotor

Two types of rotors for induction machine:Cage Rotor

Wound Rotor


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UCFCage Rotor

A cage (or squirrel-cage) rotor consists of a series of conducting bars

laid into slots carved in the face of the rotor and shorted at either end

by large shorting rings.

skewed


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UCFWound Rotor (1)

A wound rotor has a complete set of three phase windings usually Y-connected.The ends of three rotor wires are tied up to slip rings on the rotors shaft, where

extra resistance can be inserted into rotor circuits for control.


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UCFWound Rotor (2)

skewed


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UCFIM Basic Concepts

statesteadyatfollowsspeed,

ssynchronouatrotatesfield,magneticinducedsrotor':

speedssynchronouatrotatesfield,magneticsstator':rotortheofspeedorspeedmechanical:

rpminspeedssynchronou120

statoronfrequencyelectrical:

S

R

S

m

esyn c

e

n

P

fn

f

B

B

B

But rotor will not follow BS.


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UCFConcept of Rotor Slip

%100

sync

msync

f

ff

s

syncm nsn )1(

)1(

)1(

syncm

syncm

fsf

s

Pfn

P

fnf

esyn c

esyn c

syn

120

2/60


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UCFRotor Electrical Frequency

rotorthetorelativeofspeed:2/

frequencyelectricalrotor:

Rr

r

P

f

f

B

Since BRfollows BS, we have:

2/P

fff rmsync

esyncmsyncr sfPsfPfff 22

)(

)(120

msyncr nnP

f


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Induction Motor Equivalent

Circuit


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UCFEquivalent Circuit of Induction Motor (1)

1 4.44 e eff mE f N

stator copper loss

0

0

4.44

4.44

4.44

R r effR m

e effR m R

R e effR m

E f N

sf N sE

E f N

effR

eff

R

eff N

N

E

E

n 0

1

RI

FromB

net

leakage


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ReR

RReRrRrR

LfXsXLsfLfLX

222

0

0

0

0

0 / RR

R

RR

R

RR

RR

jXsRjsXRjXR

EEEI


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1:eff

n

per phase equivalent circuit

0

2

2

2

2

Reff

Reff

XnX

RnR


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UCFThevinin Equivalent Circuit

Thevinin equivalent circuitMc

McMcM

jXR

XjRjXRZ

//

11

11

11

)(

)//(

jXRZ

jXRZjXRZZ

M

M

MTH

THTHTH jXRZ

VV

11 jXRZ

Z

M

MTH


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UCFInduction Motor Power Flow


17/37

UCFPower and Torque (1)

2

2

2

InI

RnR

effR

Reff


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UCF

Per Phase Equivalent Circuit with Rotor Loss and

Converted Power Separated


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Induction Motor Torque Speed

Characteristics


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UCFInduced Torque from Physical Standpoint (1)

netRind k BBT sinnetRind BkBT


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)()()()( dcba

sin

sinnetRind BkBT

s


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UCFThevinin Equivalent Circuit

Thevinin equivalent circuitMc

McMcM

jXR

XjRjXRZ

//

11

11

11

)(

)//(

jXRZ

jXRZjXRZZ

M

M

MTH

THTHTH jXRZ

VV

11 jXRZ

Z

M

MTH


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UCFInduced Torque Equation

])()/[(

/32

2

2

2

22

XXsRR

sRVT

THTHsyn c

THin d

syn c

AGind

PT

])()[(

322

2

2

2

2

2

sXXRsR

sRVT

THTHsyn c

THind


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28/37

UCFTorque Speed Characteristic (2)


29/37

UCFConverted Power vs Speed Characteristic


30/37

UCFEffect of R2


31/37

UCFMaximum (Pullout)Torque

])()/[(

/32

2

2

2

22

XXsRR

sRVTTHTHsyn c

THin d

2222

2)(0)/( XXRs

R

sR

TTHTHin d

])([2

32

2

2

2

max

XXRR

VT

THTHTHsyn c

TH

2

2

2

2max

)( XXR

Rs

THTH

has no relationship with R2and s


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Appendix - Examples


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UCFExample 1

details in im1.m


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UCFExample 2

details in im2.m


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UCFExample 3

details in im3.m


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UCFExample 5

details in im5.m

cR

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Induction Motor Fundamentals.pdf