Principle
of DC generator
The DC
Generator works on the principle of the dynamically induced emf. Whenever
conductor cuts the flux, dynamically induced emf in it according to the
Faraday’s law of electro – magnetic induction.
What are
the essential conditions for the generation of emf?
The essential conditions for the generation of emf is
A magnetic
field
Conductor
and
Interaction
of flux between them
Describe
the function of commutator in the DC Generator.
Function of
commutator
The current
induced in the armature of the DC Generator is alternating. The function of the
commutator is to convert alternating current into unidirectional.
Describe
the function of following parts in the DC Generator: Pole, Pole shoes, Yoke, Field coil, Armature
core
Pole
The
function of the pole is to carry field winding.
Pole shoes
The
function of the pole shoes is to (1) spread flux in the air-gap (2) to support
the field winding.
Yoke
It provides
mechanical support for the pole and whole machine.
It carries
the flux path which is produced by poles.
Field coil
The
function of the field coil is to produce flux which is cut by armature.
Armature
core
The main
function of the armature core is to provide low reluctance path of field flux.
Describe
the function of air duct in the armature of the DC Generator.
Function of
air duct
The
function of air duct in the armature of the DC Generator is to cooling the
armature.
Why the
commutator segments are built with V – shaped grooves?
Commutator
segments
The
commutator segments are built with V – shaped grooves in order to prevent them
to flying out during rotation of the armature.
Which type
of joint is used between brush and brush - holder?
Pig – tail
Explain the
terms: Pole pitch, Coil span, Active conductor, Full pitch coil, Short pitch
coil
Pole pitch
The
distance between two adjacent poles is called as pole pitch.
OR
The number
of slots per pole is called as pole pitch.
OR
The
periphery of the armature divided by the number of poles of the DC Generator is
known as pole pitch.
Coil span
The
distance between coil sides of an armature coil is called as coil span.
Active
conductor
The length
of conductor lying in the magnetic field and in which an emf is induced is
called as active conductor.
Full pitch
coil
When pole
pitch is equal to coil span, it is called as full pitch coil.
Short pitch
coil
When coil
span is not equal to the pole pitch, it is called as short pitch coil.
How the
numbers of parallel paths in the armature winding affect the voltage rating and
current rating of the DC Generator?
As the
numbers of parallel paths increases in the armature winding, the voltage rating
of the armature winding does not affected but current rating increases.
Why the
values of front pitch and back pitch in the armature winding have odd value?
The value
of front pitch and back pitch must be odd otherwise it is difficult to place
coils in the slot of the armature.
Which
winding is also called as parallel winding? Lap winding or wave winding? Why?
Parallel
winding
The lap
winding is also called as parallel winding because there are numbers of
parallel path in the armature is equal to numbers of poles.
Which winding
is also called as series winding? Lap winding or winding? Why?
Series
winding
The wave
winding progresses in one direction round the armature in series of waves
therefore it is also called as series winding.
Describe
the function of dummy coil. Why it is used only in the wave winding?
Function of
Dummy coil
The dummy
coils are used in the wave winding when the requirement of the armature winding
is not met by standard armature slots. It does not affect the electrical
characteristics of the armature winding because it is not connected to the
commutator segment. The winding ends of the dummy coils are taped. It provides
only mechanical balance to the armature winding.
Which
winding is suitable for higher voltage rating Generator? Lap winding or Wave
winding? Why?
The wave
winding is suitable for higher voltage rating Generator because for the same
voltage and numbers of poles, the lap winding required higher numbers of
conductors than the wave winding.
How many
numbers of parallel paths in the simplex, duplex and triplex wave winding?
Numbers of
parallel paths
Simplex
wave winding
Two
parallel path
Duplex wave
winding
Four
parallel path
Triplex
wave winding
Six
parallel path
Describe
the different types of DC Generators.
Types of DC
Generators
Separately
excited DC Generator
DC series
Generator
DC shunt
Generator
DC compound
Generator
How self
excited Generator is different from separately excited Generator?
Self
excited generator – Separately excited generator
The self
excited Generators are those in which field winding is excited by the current
produced by the Generator itself. The separately excited Generators are those
in which field winding is excited by the separate Direct current source.
Why the
fields winding in the DC series Generator have thick wire?
The field
winding of the DC series Generator is connected in series with the armature
winding so it carries full load current. Therefore the Series Generator
consists of few turns having thick wire.
Which type
of brush material have higher voltage drop?
Carbon
brush
How many
parallel paths are there in 6 – pole wave wound DC Generator?
There are always two parallel paths in the wave winding and it will be not affected by numbers of poles.
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