2. DC Machines:
A DC Machine is an electro-mechanical energy conversion
device.
The output of the DC machine is DC output because they convert
AC voltage to DC voltage.
The conversion of this mechanism is known as the commutator,
thus these machines are also named as commutating machines.
Working principle of DC machine:
The working principle of a DC machine is when electric current
flows through a coil within a magnetic field, and then the magnetic
force generates a torque which rotates the dc motor.
3. Types of DC machines:
Following are the two types of dc machines:
DC Generators.
DC Motors.
DC generator:
An Electrical Generator is a machine which converts
mechanical power into electrical energy power.
It is based on the principle of production of dynamically induced
e.m.f.
Whenever a conductor cuts magnetic flux, dynamically induced e.m.f.
is produced in it according to Faraday's Law's of Electromagnetic
Induction
4. Electromotive force is induced by the relative motion of the
armature conductors and the magnetic field.
Construction:
It consists of following parts:
Stator:
The the magnetic fields where the coils spin. This stator is an
essential part of the DC generator, and the main function of this is
to provide includes stable magnets, where two of them are with
reverse poles facing. These magnets are located to fit in the region
of the rotor.
Rotor or Armature Core:
Rotor or armature core is the second essential part of the DC
generator, and it includes slotted iron laminations with slots that are
stacked to shape a cylindrical armature core.
5. Magnetic field:
This field envelops the armature and the current within. It is created by
permanent magnets or electromagnets.
Armature:
The armature is a coil of wire that generally consists of many windings
mounted on a shaft.
Brushes:
The brushes are made of carbon. These are rectangular block shaped. The
only function of these carbon brushes of DC generator is to collect current
from commutator segments. The brushes are housed in the rectangular box
shaped brush holder or brush box.
Commutator:
The commutator plays a vital role in DC generator. It collects current from
armature and sends it to the load as direct current. It actually takes
alternating current from armature and converts it to direct current and then
send it to external load.
6. • It connects between the rotating armature conductors and
stationary external circuit by the brushes.
Faraday’s law of electromagnetic induction.
• This law states that when a conductor moves in a magnetic
field it cuts magnetic lines of force, which induces an
electromagnetic force (EMF) in the conductor.
• The magnitude of this induced EMF depends upon the rate
of change of flux(magnetic line force). This EMF will cause
a current to flow if the conductor circuit is closed.
Working principle:
Whenever a conductor is moved within a magnetic
field in such a way that the conductor cuts across
magnetic lines of flux, voltage is generated in the
7. The AMOUNT of voltage generated depends on: the strength of the
magnetic field, the angle at which the conductor cuts the magnetic
field, the speed at which the conductor is moved, and the length of the
conductor within the magnetic field
The direction of the current can be determined by Flemming’s right
hand Rule. This rule says that if you stretch thumb, index finger and
middle finger of your right-hand perpendicular to each other, then
thumbs indicates the direction of motion of the conductor, index finger
indicates the direction of magnetic field,
8. The waveform of the current through the load circuit is as shown in
the figure. This current is unidirectional.
DC MOTOR:
A DC motor is an electric motor that runs on direct current
power. In any electric motor, operation is dependent upon simple
electromagnetism.
It is a device which converts electrical energy to mechanical
energy.
It works on the fact that a current carrying conductor placed
in a magnetic field experiences a force which causes it to rotate
with respect to its original position.
9. Constuction:
The Stator:
Every electric motor has two essential parts: one
stationary, and one that rotates. The stationary part is
the stator. Though configurations vary, the stator is most
often a permanent magnet or row of magnets lining the
edge of the motor casing,
The Rotor:
Inserted into the stator is the rotor, usually consisting of
copper wire wound into a coil around an axle. It is the
rotating part.
10. Magnetic field:
This field envelops the armature and the current within. It is
created by permanent magnets or electromagnets.
Armature:
The armature is a coil of wire that generally consists of many
windings mounted on a shaft.
Brushes:
The brushes are contacts pressing lightly against the split-ring
commutator. They provide the conducting path for the current
from a DC electrical supply to the commutator.
Split-ring commutator:
An electric motor has another important component, the
commutator, which sits at one end of the coil. It is a metal ring
11. It reverses the electrical current in the coil each time the coil rotates half
a turn. The commutator periodically reverses the current between the
rotor and the external circuit, or the battery. This ensures that the ends
of coils do not move in opposite directions, and ensures that the axle
spins in one direction.
DC current:
A current from an electrical DC supply such as a battery.
Working principal:
The working of DC motor is based on the principle that when a
current carrying conductor is placed in a magnetic field, it
experiences a mechanical force.
The direction of the mechanical force is given by:
Fleming’s Left-hand Rule and its magnitude is given by F =
12. The working of the AC motor (Induction motor and
Synchronous Motor) is different from the DC motor.
13. Consider a part of a multipolar DC motor as shown in the figure below.
When the terminals of the motor are connected to an external source of DC
supply:
•the field magnets are excited developing alternate North and South poles
•the armature conductors carry currents.
