chapter 4 dc machine Dristi (PDF)

P re p a re d B y :
Dri s ti Da tta
L e c t u re r, VU

In t ro duc t io n t o
DC Mac h in e

Cont ent s
u Overview of Direct Current Machines
u Const ruct ion
u Principle of Operat ion
u Types of DC Machine
u Power Flow Diagram
u Speed Cont rol

LEARNING OBJECTIVES
uUpon complet ion of t he chapt er t he
st udent should be able t o:
uSt at e t he principle by which machines
convert mechanical energy t o elect rical
energy.
uDiscuss t he operat ing dif f erences bet ween
dif f erent t ypes of generat ors
uUnderst and t he principle of DC generat or
as it represent s a logical behavior of dc
mot ors.

Overview of Direct Current Machines
u Direct -current (DC) machines are divided int o dc generat ors and dc
mot ors.
u Most DC machines are similar t o AC machines: i.e. t hey have AC
volt ages and current wit hin t hem.
u DC machines have DC out put s j ust because t hey have a mechanism
convert ing AC volt ages t o DC volt ages at t heir t erminals.
u This mechanism is called a commut at or ; t herefore, DC machines are
also called commut at ing machines.
u DC generat ors are not as common as t hey used t o be, because direct
current , when required, is mainly produced by elect ronic rect ifiers.
u While dc mot ors are widely used, such aut omobile, aircraft , and
port able elect ronics, in speed cont rol applicat ions…

DC Generat or
u A dc generat or is a machine t hat
convert s mechanical energy int o
elect rical energy (dc volt age and current )
by using t he principle of magnet ic
induct ion.
u In t his example, t he ends of t he wire
loop have been connect ed t o t wo slip
rings mount ed on t he shaft , while
brushes are used t o carry t he current
from t he loop t o t he out side of t he
circuit.

Principle of magnetic induction in DC machine

DC Mot or
u DC mot ors are everywhere! In a house, almost every mechanical
movement t hat you see around you is caused by an DC (direct
current ) mot or.
u An dc mot or is a machine t hat convert s elect rical energy int o
mechanical energy by supplying a dc power (volt age and current ).
u An advant age of DC mot ors is t hat it is easy t o cont rol t heir speed
in a wide diapason.

Const ruct ion of DC machine

Cutaway view of a dc motor

Stator with poles visible.

Const ruct ion of DC machine
segments

Rotor of a dc motor.

brushes

Const ruct ion of DC machine
Rotor is the rotating part - armature
Stator is the stationary part - field

Armature coil

Brushes

Stator: non-moving coil
Rotor: rotating part