The document discusses DC machines which can operate as either motors or generators depending on the direction of power flow. A DC machine consists of a static electromagnetic or permanent magnetic field and a rotating armature. The field produces a magnetic medium and the armature produces voltage and torque under the action of the magnetic field. An advantage of DC motors is their speed is easy to control over a wide range, while DC generators are now quite rare. Most DC machines have AC voltages and currents internally but produce DC outputs via a commutator mechanism.

2.  The same physical dc machine can operate as either motor or a
generator & it depends on direction of power flow
DC Machine
 DC Generator DC Motor

3. • Basically consists of
1. An electromagnetic or permanent magnetic structure called
field which is static
2. An Armature which rotates
3. The Field produces a magnetic medium
4. The Armature produces voltage and torque under the action
of the magnetic field

4. Introduction of DC Motors

DC power systems are not very common in the contemporary
engineering practice. However, DC motors still have many practical
applications, such automobile, aircraft, and portable electronics, in
speed control applications…
 An advantage of DC motors is that it is easy to control their speed in
a wide diapason.
DC generators are quite rare.
 Most DC machines are similar to AC machines: i.e. they have AC
voltages and current within them. DC machines have DC outputs just
because they have a mechanism converting AC voltages to DC
voltages at their terminals. This mechanism is called a commutator;
therefore, DC machines are also called commutating machines.

5. DC Motor
The direct current (dc) machine can be
used as a motor or as a generator.
DC Machine is most often used for a motor.
The major advantages of dc machines
are the easy speed and torque regulation.
However, their application is limited to mills,
mines and trains. As examples, trolleys and
underground subway cars may use dc motors.
In the past, automobiles were equipped
with dc dynamos to charge their batteries.

6. DC Machine Construction
General arrangement of a dc machine

7. DC Machines
 The stator of the dc motor has
poles, which are excited by dc
current to produce magnetic
fields.
 In the neutral zone, in the middle
between the poles, commutating
poles are placed to reduce
sparking of the commutator.
The commutating poles are
supplied by dc current.
 Compensating windings are
mounted on the main poles.
These short-circuited windings
damp rotor oscillations.

8. DC Machines
 The poles are mounted on
an iron core that provides a
closed magnetic circuit.
 The motor housing supports
the iron core, the brushes
and the bearings.
 The rotor has a ring-shaped
laminated iron core with
slots.
 Coils with several turns are
placed in the slots. The
distance between the two
legs of the coil is about 180
electric degrees.

9. DC Machines
 The rotor has a ring-shaped
laminated iron core with slots.
 The commutator consists of
insulated copper segments
mounted on an insulated tube.
 Two brushes are pressed to the
commutator to permit current
flow.
 The brushes are placed in the
neutral zone, where the
magnetic field is close to zero,
to reduce arcing.

10. DC Machines
 The rotor has a ring-shaped
laminated iron core with slots.
 The commutator consists of
insulated copper segments
mounted on an insulated tube.
 Two brushes are pressed to the
commutator to permit current
flow.
 The brushes are placed in the
neutral zone, where the
magnetic field is close to zero,
to reduce arcing.