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

DC GENERATORS

ROTATING MACHINES - SAME CONSTRUCTION AS MOTORS:

GENERATORIC RUN = 1 working status of DC machine

• SUPPLY = EXTERNAL MOVER - mechanical energy

• GENERATOR - converts mechanical into electrical DC

DC GENERATOR = DYNAMO

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

CROSS-SECTION VIEW DC MACHINE

gn

N1

N2

stator

rotor(armature)

n

If

Ia

pole

air gap

field winding

armaturewinding

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

PRINCIPLES OF OPERATION

ua

ia

B1

B2

-

+

+

-ui1

ui2

+

-

t

u

ui1

ui2

ua

Ua

duration of 1 turn

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

GENERATOR ACTION

lBve

)(

)(222 BlrBlrBlve

0 0

.21

.1

dlrBdeeav

0

222BAdaBeav

.. cUE iav

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

MAGNETIZATION CURVE

If-If

U0

-U0

A

B

C

D

Ur = k.IfFm = Nf .If ~

~SATURATIONLINEAR

REMANENTMAGNETIZATION

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

COMMUTATION PROCESS

If

If

g

n

f

a Ia

n

n

a

f

g

n

SHIFTED NEUTRAL AXIS

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

AUXILIARY COMMUTATION POLES

f

f

aip

ipn

main poles

auxiliary poles(interpoles)

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

ARMATURE REACTION

N SN NS

p

magnetic field of main poles

magnetic field of armature and interpoles

resulting magnetic field

DEFORMATIONdue to armature

reaction

MAIN POLES INTERPOLES

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

cn

e2

aai icin

T

2

dt

diLiRu f

ffff

edt

diLiRu a

aaaa dt

dJTTT mi

BASIC EQUATIONS OF DC GENERATORS

BEHAVIOR DEPENDS ON WINDINGS INTERCONNECTION

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

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

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

SEPARATELY EXCITED GENERATOR

UaUiRf,Lf

If

Ia

load

Uf

edt

diLiRu a

aaaa

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

VOLT-AMPERE (LOAD) CHARACTERISTICS

U

Ia

In

Ua0

Ui

Ui-RaIaUa

Uan

Difference due to ARMATURE

REACTION

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

SHUNT GENERATOR

Ua

I

UiRf,Lf

If

Ia

load

Rfr fa uu

fa iii

dt

diLiRiRu f

fffrfff

edt

diLiRu a

aaaa

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

EXCITATION OF SHUNT GENERATOR

Ui

If

Ui (If )

U = Rfc . If

A1A2A3

Ur

frffc RRR

! POLARITY of the field winding !

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

COMPARISON OF GENERATORS

U

Ia

In

Isc

sep. excited

shunt

series

SHUNT: nsc II welding machines