ems ch13 ppt

UNIVERSITY OF TECHNOLOGY, SYDNEYUNIVERSITY OF TECHNOLOGY, SYDNEYFACULTY OF ENGINEERINGFACULTY OF ENGINEERING

48531 Electromechanical Systems48531 Electromechanical Systems

Introduction to ConventionalIntroduction to ConventionalAC and DC MachinesAC and DC Machines

Topics to cover:

1. Introduction 2. DC Machines

3. Synchronous Machines 4. Induction Machines

IntroductionIntroductionConventional rotating machines are very commonly used inindustrial drive systems. They can be energized either directly byconventional AC and DC power supplies, or by power electronicconverters/inverters, especially in varibale speed drives.

According to the operational principles and power supplies, they canbe classified as:

DC machines, -- DC power supplies;

Synchronous machines, -- speeds proportional to the supply

frequency; and

Induction machines, -- rotor emf and current are induced by

rotating magnetic field

DC MachinesDC Machines- Basic Principles: Induced emf- Basic Principles: Induced emf

Induced emf in elementary AC and DC machines

DC MachinesDC Machines- Basic Principles: Electromagnetic Torque- Basic Principles: Electromagnetic Torque

Uni-directional torque inan elementary DC machine

DC MachinesDC Machines- Structures: Electromagnet Poles- Structures: Electromagnet Poles Cut away view of

a DC Machine

DC MachinesDC Machines- Structures: Electromagnetic Poles (Cont.)- Structures: Electromagnetic Poles (Cont.)

Cross section ofa DC machine

DC MachinesDC Machines- Structures: Permanent Magnet Poles- Structures: Permanent Magnet Poles

Dis-assembled view ofa PM DC Machine

DC MachinesDC Machines- Structures: Permanent Magnet Poles (Cont.)- Structures: Permanent Magnet Poles (Cont.)

Cross section of aPM DC Machine





DC MachinesDC Machines- Windings- Windings

A DC machinewinding (lap)

DC MachinesDC Machines- Induced Emf- Induced Emf

Waveforms of induced emf

DC MachinesDC Machines- Schematic Representation- Schematic Representation

Symbol of a DC machine

DC MachinesDC Machines- Field Circuit Connection- Field Circuit Connection

Four field circuit connections

DC MachinesDC Machines- Emf and Torque- Emf and Torque

Assume the flux linkage of a single turn coil due to the stator magnetsvaries with time sinusoidally:

The induced emf then can be calculated by

The commutator rectifies AC into DC, and

therefore,

λ λ ωs m m t= 2 s in

ed

d ttm= =

ΦΦω ωco s

e td ta m m= =∫1 2

2

3 2

πω ω ω

πω

π

πΦ Φco s

For an armature winding of a great number of coils, the emf is

The electromagnetic power must balance the internal mechanicalpower, or Therefore,P E I Tem a a em r= = ω

TP

K Iemem

ra m a= =

ωΦ

E Ka a m r= Φ ω

DC MachinesDC Machines- Equivalent Circuit: Generator- Equivalent Circuit: Generator

Equivalent circuit of a separateexcited generator

DC MachinesDC Machines- Equivalent Circuit: Motor- Equivalent Circuit: Motor

Equivalent circuit of aseparately excited DC motor

DC MachinesDC Machines- DC Generators- DC Generators

Conditions for terminalvoltage build-up:

1) Residual magnetism

2) Connection ofarmature winding tofield winding such thatthe generated field aidsthe residual magneticfield;

3) The field circuitresistance smaller thanthe critical resistance

DC MachinesDC Machines- DC Generators (Cont.)- DC Generators (Cont.)

External characteristics of different DC generators

DC MachinesDC Machines- Drive Systems- Drive Systems

Ward-Leonard System

DC MachinesDC Machines- Drive Systems (Cont.)- Drive Systems (Cont.)

Power Electronic Drive System

0

Separately Excited

Shunt Motor

Series Motor

Motor

Compound Motorω0

DC MachinesDC Machines- Torque/Speed Curves- Torque/Speed Curves

Torque/speed curves of different DC motors

Synchronous MachinesSynchronous Machines- Structures: Generators- Structures: Generators

Hydroelectric synchronous generator


Hydroelectricsynchronousgenerator


Stator of aturbinegenerator


Rotor of a turbine generator

Synchronous MachinesSynchronous Machines- Structures: Motors- Structures: Motors

Synchronous motor

Synchronous MachinesSynchronous Machines- Structures: Motors- Structures: Motors

Permanent magnet motors

Synchronous MachinesSynchronous Machines- Electrical and Mechanical Engles- Electrical and Mechanical Engles

Elementary two polesynchronous machine

Synchronous MachinesSynchronous Machines- Electrical and Mechanical Engles (Cont.)- Electrical and Mechanical Engles (Cont.)

Elementary four polesynchronous machine

θ θ=P

m2ω ω=

Pm2and

Synchronous MachinesSynchronous Machines- Rotating Field (Cont.)- Rotating Field (Cont.)

Phase winding positionsand phase currents


Positions of rotating field at different time

t=0

θπ/ 2 π π/ 23 π20

F1

t= ωπ

2ω


Rotating mmf wave

( )F F F FF

ta b cm

1 1 1 1

3

2= + + = −cosθ ω


The speed in electrical rad/s of the rotating field is

ωθ π

π ωωf

d

dt= = =

2

2

ωω

f P=

2

nf

Pf

f= =60

2

120ωπ

In rev/min, it is

In mechanical rad/s,

Synchronous MachinesSynchronous Machines- Equivalent Circuit- Equivalent Circuit

Equivalent Circuit for synchronous (a) genarators and (b) motors

(Xs>>Ra for large synchronous machines)

Ea

jXs Ra Ia

Va Ea

jXs Ra Ia

Va

(a) (b)

Synchronous MachinesSynchronous Machines- Phasor Diagrams- Phasor Diagrams

Phasor diagrams for synchronous (a) genarators and (b) motors(a) (b)

Va

I a

jXsI a

δEaϕVa

I a

jXsI a

δϕ

Ea

Synchronous MachinesSynchronous Machines- Generator Characteristics- Generator Characteristics Synchronous MachinesSynchronous Machines

- Torque/Load Angle Curve- Torque/Load Angle Curve

TE V

Xa a

f s

=3

ωδsin

InductiveLoad

SynchronousCondenser

Three PhasePower Supply I loadI s

I cmp

Synchronous MachinesSynchronous Machines- Power factor Compensation- Power factor Compensation

Schematic illustration of power factor compensationusing synchronous condensers

( ) ( )Im ImI Icmp load= −

Ea sinδ

I a cosϕ

I a2

δδ 1

ϕ3

Ea1 Ea2 Ea3

Va

jX sI a1 jX sI a2

jX sI a3

I a3

δδ 2 δδ 3ϕ

1

I a1

Synchronous MachinesSynchronous Machines- Power factor Compensation (Cont.)- Power factor Compensation (Cont.)

Phasoe diagram of power factor control by controlingrotor excitation of a synchronous machine

Synchronous MachinesSynchronous Machines- V Curves- V Curves Synchronous MachinesSynchronous Machines

- Speed Control- Speed Control

Synchonous motor speedcontrol: Variable Voltageand Variable Frequency(VVVF)

Induction MachinesInduction Machines- Structures- Structures

Cut away viewof a wound rotorinduction motor

Induction MachinesInduction Machines- Structures- Structures

Wound rotorof an inductionmotor

Induction MachinesInduction Machines- Structures (Cont.)- Structures (Cont.)

Cut away view ofa squirrel cageinduction motor

Induction MachinesInduction Machines- Structures (Cont.)- Structures (Cont.)

Squirrel cagerotor of aninduction motor

Induction MachinesInduction Machines- Equivalent Circuit- Equivalent Circuit

T equivalent circuit of induction motors

V 1

I 1R1 jX l1

jX m

jX'l2R'2 I'2

E 1R'2

1-ss

where slip sf r

f

=−ω ω

ω

Induction MachinesInduction Machines- Torque/Speed Curve- Torque/Speed Curve

( )T

VR

s

RR

sX Xf

l l

=+

+ +

3 12 2

12

2

1 2

2ω

'

''

Induction MachinesInduction Machines- Speed Control- Speed Control

Methods for induction motor speed control:

1) Varying number of poles,

2) Varying terminal voltage,

3) Varying rotor winding resistance,

4) Rotor power recovery, and

5) Variable voltage variable frequency (VVVF).

Induction MachinesInduction Machines- Speed Control (Cont.)- Speed Control (Cont.)

Induction motor speed control by varying number of poles


Induction motor speed control by varying number of poles


Induction motorspeed control byvarying terminalvoltage


Induction motorspeed control byvarying rotorwinding resistance


Induction motor speed control by rotor power recovery


Induction motor speed control by variable voltagevariable frequency (VVVF).


Torque/speedcurve of VVVFspeed control

ems ch13 ppt

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