❖Principle of Operation of DC Generator
❖Different Parts of a DC Generator and their
Functions
Classification of Electrical
Machines
Construction of simple loop DC
Generator
A Generator is a Machine that converts
Mechanical energy into Electrical energy.
9. DC Generator
➢A DC generator is an Electrical Machine which
converts Mechanical energy into Electrical Energy
(DC).
➢The Energy conversion is based on Faraday’s Law
of Electromagnetic Induction.
11. Yoke
➢The outer frame of a generator or motor is called as yoke. Yoke is made
up of cast iron or steel.
➢Yoke provides mechanical strength for whole assembly of the generator
(or motor).
➢It also carries the magnetic flux produced by the poles.
Construction:
For small generators:
cast iron
for large generators :
cast steel or
rolled steel
12. Poles Cores and Pole Shoe
➢Pole cores and pole shoes are the component of field magnet
➢Poles are joined to the yoke with the help of screws or welding.
➢Poles are to support field windings.
➢Field winding is wound on poles and connected in series or parallel
with armature winding or sometimes separately.
➢Pole shoe is an extended part of the pole which serves two purposes,
(1) to support exciting coils (field coils)
(2) to spread out the flux in air gap uniformly.
14. Armature Core
➢Armature core is the rotor of a generator.
➢Armature core is cylindrical in shape on which slots are
provided to carry armature windings.
➢to provide a path of very low reluctance to the flux
through the armature from a N-pole to a S-pole
15. Commutator Brushes & Bearings
➢function of the commutator is to facilitate collection of
current from the armature conductors
➢it rectified i.e. converts the alternating current induced
in the armature conductors into unidirectional current
in the external load circuit
➢Each commutator segment is connected to the
armature conductor by means of a copper lug or strip
(or riser)
➢To prevent them from flying out under the action of
centrifugal forces, the segments have V-grooves, these
grooves being insulated by conical micanite rings
16. Commutator and Brushes
➢Conducting brushes rest on commutator and they slides over
when rotor (hence commutator) rotates.
➢Thus brushes are physically in contact with armature conductors
hence wires can be connected to brushes.
23. Faraday’s Law of
Electromagnetic Induction
➢According to this law, when an conductor moves in a
magnetic field it cuts magnetic lines of force, due to
which an emf is induced in the conductor.
➢The magnitude of this induced emf depends upon the
rate of change of flux (magnetic line force) linkage with
the conductor.
➢This emf will cause an current to flow if the conductor
circuit is closed.
24. Basic Parts of a Generator
The two basic essential parts of an generator are
1) a Magnetic Field and
2) Conductors which move inside that Magnetic Field.
25. ➢ Fleming's Right-hand Rule (for generators) shows the direction
of induced current when a conductor attached to a circuit moves in
a magnetic field. It can be used to determine the direction of
current in a generator's windings.
Fleming's Right-hand Rule
28. Principle of Operation of DC
Generator
➢ 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
conductor.
➢ 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
29. ➢An elementary generator consists
of a wire loop mounted on the
shaft, so that it can be rotated in a
stationary magnetic field.
➢This will produce an induced emf
in the loop.
➢The pole pieces (marked N and S)
provide the magnetic field. The pole
pieces are shaped and positioned as
shown to concentrate the magnetic
field as close as possible to the wire
loop.
Principle of Operation of
DC Generator
30. ➢The loop of wire that rotates through the
field is called the ARMATURE. The ends of
the armature loop are connected to rings
called SLIP RINGS.
➢The brushes, usually made of carbon,
with wires attached to them, ride against
the rings. The generated voltage appears
across these brushes. Sliding contacts or
brushes connect the loop to an external
circuit load in order to pick up or use
the induced emf
Principle of Operation of DC
Generator
