DC GENERATOR
BY SHUBHAM KUMAR
EN 2ND YEAR
CONTENTS
1. Generator Principle, Construction & working
2. Parts of a Generator
3. EMF Equation of a Generator
What is a Generator?
A generator is a machine that converts
Mechanical energy into Electrical energy.
What is an 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.
Principle
Faraday’s Law of Electromagnetic
Induction
Faraday’s Law of Electromagnetic Induction
According to these 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.
Basic Essential Parts
The two basic essential parts of an generator are
1) a magnetic field and
2) conductors which move inside that magnetic field.
Parts of a DC Generator
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.
Yoke
Poles
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
Pole shoe is an extended part of the pole which serves two
purposes,
(1) to prevent field coils from slipping and
(2) to spread out the flux in air gap uniformly.
Pole and Pole Shoe
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.
Commutator and brushes
As emf is generated in the armature conductors terminals must be
taken out to make use of generated emf.
But if we can't directly solder wires to commutator conductors as
they rotates.
Thus commutator is connected to the armature conductors and
mounted on the same shaft as that of armature core.
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.
Working
Simple Loop of Conductor
Working
Working
Working
EMF Equation a DC Generator
Let Ø = flux/pole in Wb (weber)
Z = total no. of armature conductors
P = no. of generator poles
A = no. of parallel paths in armature
N = rotational speed of armature in revolutions per min. (rpm)
E = emf induced in any parallel path in armature
EMF Equation a DC Generator
EMF Equation a DC Generator
volts
EMF Equation a DC Generator
Classification of DC Generator
1.DC machines (i.e. DC generators or DC motors) can be classified on the basis of configuration of
their excitation winding.
2.Field winding may be connected to armature winding (in series or parallel) or it may be separately
excited.
3.This divides DC machines in two main types
4. Self Excited
5. Separately Excited
Classification of DC Generator
Generally DC generators are classified according to the ways of
excitation of their fields. There are three methods of excitation.
● Field coils excited by permanent magnets – Permanent magnet DC generators
● Field coils excited by some external source – Separately excited DC generators
● Field coils excited by the generator itself – Self excited DC generators
Permanent magnet DC generators
Permanent magnet DC generators
● When the flux in the magnetic circuit is established by the help of
permanent magnets then it is known as Permanent magnet dc generator.
● It consists of an armature and one or several permanent magnets
situated around the armature.
● This type of dc generators generates very low power.
● So, they are rarely found in industrial applications.
● They are normally used in small applications like dynamos in motor
cycles.
Separately Excited DC Generator
● These are the generators whose field magnets are energized by some
external dc source such as battery .
Self-excited DC Generators
● These are the generators whose field magnets are energized by the
current supplied by themselves.
Series Wound Generator
● In these type of generators, the field windings are connected in series with
armature conductors
Shunt Wound DC Generators
● In these type of DC generators the field windings are connected in parallel
with armature conductors.
Compound wound generators
● Compound wound generators have both series field winding and shunt
field winding.
● One winding is placed in series with the armature and the other is placed
in parallel with the armature.
Cumulative and Differential Compound
Generator
● In a compound wound generator, the shunt field is stronger than the series
field.
● When the series field assists the shunt field, generator is said to be
commutatively compound wound.
● On the other hand if series field opposes the shunt field, the generator is
said to be differentially compound wound.
THANK YOU
