dc machines -...

DC MACHINES

AE1BSP1

Doc. Ing. Pavel Pivoňka, Csc.

©NOTES - Doc. Ing. Pavel Pivoňka, CSc.

TYPICAL DC MACHINE

DC ROTATING MACHINE CAN WORK EITHER AS A MOTOR OR A GENERATOR


DC MACHINE MAIN PARTS

CONDUCTORS from supply ARMATURE winding

COMMUTATOR

HOLDER with BRUSHES

ROTOR CORE from iron sheets

PERMANENT MAGNETS (or excitation winding)


CROSS-SECTION VIEW DC MACHINE

gn

N1

N2

stator

rotor(armature)

n

φ

If

Ia

pole

air gapδ

field winding

armaturewinding


Ua

Ui

Ra,La

Ia

Rf,LfIf

Uf

SCHEMATIC DRAWINGS

FIELD WINDING ARMATURE WINDING

BEHAVIOR DEPENDS ON WINDINGS INTERCONNECTION


THREE BASIC TYPES OF DC MACHINES

Ua

I

UiRf,Lf

If

Ia

Rfr

UaUiRf,LfIf

Ia

Uf

Ua

If=Ia

UiRf,Lf

IfIa

SEPARATELY EXCITED SERIES SHUNT

(also permanent magnet)

COMPOUND MACHINE = combination of shunt and series


PRINCIPLES OF OPERATION

ω

-

+

+

-ui1

ui2

φ t

u

ui1

ui2

duration of 1 turn

ua

ia

+

-

N SN NS

τp

magnetic field of main poles

dtdAB

dtdue i =Φ

==

lBvue i

•×== )(


GENERATOR ACTION

lBve

•×= )(

)(222 Θ=== BlrBlrBlve ωω

∫ ∫ Θ⋅=Θ⋅=π π

ωππ 0 0

.21.1 dlrBdeeav

∫ Φ==⋅⋅=π

ωπ

ωπ

ωπ 0

222 BAdaBeav

ω..Φ== cUE iav

ua

ia

B1

B2

ω

-

+

+

-ui1

ui2

+

- φ

t

u ua

Ua

duration of 1 turn

IF Ra = 0 Ua=Ui=Eav


ωωπ

⋅Φ⋅=⋅Φ⋅⋅

= cne 2

aai icinT ⋅Φ⋅=⋅Φ⋅⋅

=π

2

dtdi

LiRu fffff ⋅+⋅=

edtdiLiRu a

aaaa +⋅−⋅−=

dtdJTTT miω

⋅+∆+=

BASIC EQUATIONS OF DC GENERATORS

UaUiRf,LfIf

Ia

Uf

aaout iup ⋅=

)( fieldin pTp +⋅= ω


SEPARATELY EXCITED GENERATOR

UaUiRf,Lf

If

Ia

load

Uf

Ui

If

Ui (If )Ua0=Uin

Ur

Ifn

edtdiLiRu a

aaaa +⋅−⋅−=


VOLT-AMPERE (LOAD) CHARACTERISTICS

U

Ia

In

Ua0Ui

Ui-RaIaUa

Uan

Difference due to ARMATURE REACTION

UaUiRf,LfIf

Ia

Uf


ARMATURE REACTION

N SN NS

τp

magnetic field of main poles

magnetic field of armature and interpoles

resulting magnetic fieldDEFORMATION due to armature

reaction

MAIN POLES INTERPOLES


COMMUTATION PROCESS

If

If

gn

φ f

φ a Ia

n

n

φ a

φ fφ

gn

SHIFTED NEUTRAL AXIS


AUXILIARY COMMUTATION POLES

φf

φf

φaφip

φipn

main poles

auxiliary poles(interpoles)


SHUNT GENERATOR

Ua

I

UiRf,Lf

If

Ia

load

Rfr fa uu =

fa iii −=

dtdi

LiRiRu ffffrfff ⋅+⋅+⋅=

edtdiLiRu a

aaaa +⋅−⋅−=


EXCITATION OF SHUNT GENERATOR

Ui

If

Ui (If )

∆U = Rfc . If

A1A2A3

Ur

frffc RRR +=

! POLARITY of the field winding !


COMPARISON OF GENERATORS

U

Ia

In

Isc

sep. excited

shuntseries

SHUNT: nsc II << welding machines


ENERGY BALANCE (POWER DIVISION)

Shunt field

Pel ω T

Series fieldBrush

ArmatureFriction

Stray-load

ELECTROMAGNETICPOWER

Ea.Ia

armature circuit 3 to 6%Pin

rotational losses 3 to 15%Pin

shunt field 1 to 5%Pin

MOTOR GENERATOR


MOTOR ACTION

)( BlIF

×⋅=

F = B . i . l . sinΘ

T = 2.F.r = 2.B.ic.l.r

∫ ∫ ⋅Φ⋅=⋅⋅=Θ⋅⋅⋅⋅⋅⋅=π π

πππ 0 0

2.221 idaBidBrliTav

aiav icTT ..Φ==


ωωπ

⋅Φ⋅=⋅Φ⋅⋅

= cne 2

aai icinT ⋅Φ⋅=⋅Φ⋅⋅

=π

2

dtdi

LiRu fffff ⋅+⋅=

edtdiLiRu a

aaaa +⋅+⋅= dtdJTTT m

miω

⋅++∆=

BASIC EQUATIONS OF DC MOTORS

BEHAVIOR DEPENDS ON WINDINGS INTERCONNECTION

• SEPARATELY EXCITED (also permanent magnet) – SEM

• SERIES – SRM

• SHUNT – SHM

Subject number 21

DC Motor Basic Description

SEPARATELY EXCITED, SEM (also permanent magnet, PMM) wide range of speed and power SHUNT, SHM SERIES, SRM high starting M, parallel operation, damped transients traction universal motors COMPOUND (combination of shunt and series)

ωωπ

Φ=Φ== capNue i

ai icT Φ=

dtdi

LiRu fffff +=

edtdiLiRu a

aaaa ++=

dtdJTTT miω

++∆=

Subject number 22

DC SEM Characteristics

STEADY STATE OPERATION Schematic picture Equations Characteristics

ΦΩ== cUE i

fff IRU =

EIRU aaa +=

TTIcT mai +∆=Φ=

Rf,Lf

If

Ia

Uf

Ui

Ra,La

Ua

Φ−

=Φ

==Ωc

IRUcE aaaω

a

aa R

EUI −=

)( aIf=ω

)(Tf=ω

0≠Φ!

Subject number 23

DC SEM speed+mechanical curves

T(Ia)

ω

0

ω0

Tn

ωn

If < Ifn; Ua = Uan; Ra

If = Ifn; Ua = Uan; Ra

If = Ifn; Ua < Uan; Ra

If = Ifn; Ua = Uan Rax = Ra + Rx

TLOAD

Φ−

=c

IRU aaaω

Φ≅

cTIaa

aaa kIc

IRcU

−=Φ

−Φ

= 0ωωΦ

=cRk a

armature reaction influence

natural characteristics

working points


INFLUENCE OF Ra ON n=f(T) CURVE

n

T

n0

Ratotal

Φ⋅⋅−

=Φ⋅

==Ωc

IRUc

E aaaω

addedaatotal RRR +=

base speed

Subject number 25

DC SEM Starting

by direct connection to Ua = Un Ia = (10 to 30) In decrease current by variable Ua or Ra

to produce sufficient torque fully excited or slightly overexcited If ≥ Ifn

Φ−

=c

IRU aaaω

max1

a

aa I

UR =

Ia (M)

ω

0

ω0

Iamax

Ra

Ra2 > Ra3 … > Ra

Ra1 > Ra2

1

2

3

Iaminmin

max

3

2

2

1 .....a

a

a

ax

a

a

a

a

II

RR

RR

RR

====

quasistationnery working points

Subject number 26

DC SEM Braking

DYNAMIC (rheostatic)

-I a

(-T)

ω

0

ω1

-Iamax

Ra

Ra2 > Ra3 … > Ra

Ra1 > Ra2

3

-Iamin

2

1Ui

Rf,Lf

Ra,La

R

Subject number 27

DC SEM Braking

REVERSE CURRENT (plugging) by active load torque by passive load torque

T

ω

0

ω1

B

Ra

R1>Ra

ω2

A

T

ω

0

ω1

Ra

R1>Ra

Subject number 28

DC SEM Braking

REGENERATIVE by decreasing armature voltage by changing load activity The power supply must be able to accept generated energy !!!

T

ω

0

ω1

ω2Ua

TLOAD

ω=0 T

ω

0

ω1

ω2

TLOAD-TLOAD

MOTORGENERATOR

Subject number 29

DC SEM Reversal

change polarity of Ua (see starting and braking) change polarity of If

Machine could be mechanically and electrically damaged If polarity change cannot be used on running machine !!!

Φ−

=Φ

=c

IRUcE aaaω

0=Φif!

0≠Φ!

Φ−=−

cEω

∞→ω

++∆=Φ=

dtdJTTIcT mai

ω ∞→aIΦ

−=

cIRU aaaω

I fIfn

ωmax

Ua=const.

ω


DC SEM Speed Change

T

ω ω

ω

Ua

If

Uan

Ifn

ωmax

Ua=const.=Uan

If = const.=Ifn

Uan ; Ifn

Ua

If

Φ⋅⋅−

=Φ⋅

==Ωc

IRUc

E aaaω constant power

constant torque

base speed

Subject number 31

DC SHM Characteristics

STEADY STATE OPERATION Schematic view Equations Characteristics

Ua

I

UiRf,Lf

If

Ia

RfrωΦ== cUE i

ffrff IRRU )( +=

EIRU aaa +=

TTIcT mai +∆=Φ=fa III −=

Φ−

=Φ

=c

IRUcE aaaω

a

aa R

EUI −=

)( aIf=ω

)(Tf=ω

Subject number 32

DC SHM Behavior

Basic behavior similar to separately excited Speed and mechanical characteristics are practically identical Starting, braking and speed control by variable Ua or Ra Reversal by changing polarity of armature or field windings

No difference in design: all SEM can work as SHM

Advantage: no separated power supply for excitation

Φ−

=c

IRU aaaωa

aa R

EUI −= aIcT Φ≅

Subject number 33

DC SRM Characteristics

STEADY STATE OPERATION Schematic picture Equations Characteristics

Ua

If=Ia

UiRf,Lf

IfIa

Ra,La

ωξω ai IcUE =Φ==

aff IRU =

ωξ aafafaaa IIRRUEIRU ++=++= )(

TTIIcT maai +∆==Φ= 2ξ

)( aIf=ω)(Tf=ω!

fa II =

0≠aIa

aatotala

IIRU

ξω −

=

ξi

aTI =

)( aIfT =

Subject number 34

DC SRM speed+torque+mechanical curves

ω

T

4

TSTART0

dtdJTTT mi

ω++∆=

advantage by start with load: ω

I a

1

2

3

4

0

T

1 3

ξ is not constant !!! (Φ=f(Ia) is not linear)

ξξξω atotal

a

a

a

aatotala RI

UI

IRU−=

−=

ξi

aTI =

1 = natural characteristics 2 = lower Ua 3 = lower If (by shunting field winding) 4 = higher Ra

ξξω atotal

i

a RT

U−=

base speed

Subject number 35

DC SRM Starting

by variable Ua

by variable Ra: ω

Ia

Ra

0

Ramax

IamaxIamin

maxmax

a

aa I

UR =

ξξω atotal

a

a RI

U−=

UaUi

Rf,LfRa Rn R1

Ramax

Subject number 36

DC SRM Braking

DYNAMIC (rheostatic)

-I a

ω

0

ω1

Ra

R1 < Rmax

Rmax

Ui

Rf,Lf

Ra,La

R

Ua

I a

Ua

0

ω1

R

ω2 < ω1

ωn

1

2

n-1

Subject number 37

DC SRM Braking

REVERSE CURRENT (plugging) by active load torque by passive load torque REGENERATIVE – possible only with chopper connected

T

ω

0

ω1

B

Ra

R1>Ra

ω2

A

TLOAD

T1T2 T

ω

0

ω1

Ra

R1>Ra

AB

C

Subject number 38

DC SRM Reversing

Not to change polarity of terminal voltage: Change armature voltage or Change field votage

T

ω

0

Ui

Rf,Lf

Ra,La

+

-

Ui

Rf,Lf

Ra,La

+

-

Ui

Rf,Lf

Ra,La

+

-

Subject number 39

DC SRM Speed Change

Variable Ra – not frequently used (high loss)

Variable Ua – most frequent

Shunting field winding (decrease If) limitations: power, commutation

Grouping by multimotor drives : serial/parallel

ξξξω atotal

a

aatotal

a

a RIc

URI

U−

Φ=−=

ω

T0

Uamax

U

Mot4Mot3Mot2Mot1

U Mot4Mot3

Mot2Mot1

ξξω atotal

i

a RT

U−=


COMPARISON OF MOTORS

ω

TTn

sep. excited and shunt

compound

series

ωn

0


STARTING AND ROTATION REVERSAL

Φ⋅⋅−

=c

IRU aaaωa

aa R

EUI −=

SEPARATELY EXCITED AND SHUNT start: by Un is Is = 10 to 30 In ----> variable Ua or Ra reversal: change polarity of Ua or If (only on not running machine - flux must not be zero !!!)

SERIES start: variable Ua - machine must not be unloaded !!! reversal: change polarity of Ua or If

aIcT ⋅Φ⋅≅

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