a brief idea regarding DC generators.

1. DC Generators

2. History of Generators

3. 1831 1852 18821867 1900
Faraday
Disc
Generator
Jedlik and
Self
Excitation
Direct
Current
Generator
Alternating
Current
Generator
Self
Excitation

4. What is a DC
Generator?
A dc generator is an electrical machine
which converts mechanical energy into
direct current electricity. This energy
conversion is based on the principle of
production of dynamically induced emf.

5. Construction of a DC generator

6. Working Principle

8. Classification of a
DC Generator
Level 1
Level 2
Level 3

9. Commutation in DC Machine or Commutation in
DC Generator or Motor
The currents induced in the armature conductors of a DC generator
are alternating in nature. The change from a generated alternating
current to the direct current
applied involves the process
of Commutation. When the
conductors of the armature
are under the north pole,
the current which is induced
flows in one direction The
current flows in the opposite
direction when they are under
south
pole.

10. Resistance Commutation
The Resistance Commutation method uses Carbon brushes
for improving commutation. The use of Carbon brushes
makes the contact resistance between commutator
segments and brushes high.
Voltage Commutation
In the Voltage Commutation method, the arrangement is
made to induce a voltage in the coil undergoing the
commutation process, which will neutralize the reactance
voltage.
Brush Shift
The effect of armature reaction is to shift the magnetic neutral axis (MNA) in the direction of rotation for the
generator and against the direction of rotation for the motor. Armature reaction establishes a flux in the neutral zone.
A small voltage is induced in the commutating coil since it is cutting the flux.
Commutating Poles or Interpoles
Interpoles are narrow poles placed in between the main poles and are attached to the stator Interpoles are also
called commutating poles or Campoles. The interpoles windings are connected in series with the armature because
the interpoles must produce fluxes that are directly proportional to the armature current.

11. Commutation and Methods of Improving
DC Machines

12. Applications of DC Machines
In the present day world, the electrical energy is generated in bulk in the form of an alternating current. Hence, the
use of DC machines, i.e., DC generators and motors are very limited. They are mainly used in supplying excitation
of small and medium range alternators.
A. Applications of DC Motors
1. Series Motors
The series DC motors are used where high starting torque is required, and variations in speed are possible. For
example – the series motors are used in Traction system, Cranes, air compressors, Vaccum Cleaner, Sewing
machine, etc.
2. Shunt Motors
The various applications of DC shunt motor are in Lathe Machines, Centrifugal Pumps, Fans, Blowers, Conveyors,
Lifts, Weaving Machine, Spinning machines, etc.
3. Compound Motors
The compound motors are used where higher starting torque and fairly constant speed is required. The examples of
usage of compound motors are in Presses, Shears, Conveyors, Elevators, Rolling Mills, Heavy Planners, etc.

13. Applications of DC Generators
A. Separately Excited DC Generators
1.Separately excited DC Generators are used in laboratories for testing as they have a
. wide range of voltage output.
2.Used as a supply source of DC motors.
B. Shunt wound Generators
1. DC shunt wound generators are used for lighting purposes.
2.Used to charge the battery.
3.Providing excitation to the alternators.
C. Series Wound Generators
1.DC series wound generators are used in DC locomotives for regenerative braking .
. for
2.providing field excitation current.
3.Used as a booster in distribution networks.
4.Over compounded cumulative generators are used in lighting and heavy power .
. supply.

14. Hope, your sacrifice of few minutes
Did not go waste!
Presented by-
Arijit Roy Chowdhury
Bhavya Jha
EE2A