1.
0 - DIRECT CURRENT (DC) GENERATOR
1.0 - DIRECT CURRENT (DC) GENERATOR
1.1 - Definition : An electrical generator is a machine which
converts mechanical energy into electrical energy. The energy
conversion is based on the principle of the production of
dynamically induced emf, where a conductor cuts magnetic
flux, dynamically induced emf is produced in it according to
Faraday’s Laws of electromagnetic Induction.
Mechanical input Electrical output
ELECTRICAL
MACHINES
- Generator -
1.1.1 - Faraday Law for Electromagnetic Induction
Faraday's Law , where Faraday states that when the flux cutting
the conductor will be induced in the E.M.F and E.M.F. conductor is
proportional to the flux cutting.
1. The explanation: Conversion of mechanical energy into electricity is
through the conductor cuts the magnetic flux in which the occurrence
of E.M.F in the conductor.
2. Mathematically, for a conductor of N turns of wire, cutting through a
magnetic flux of Δ in a time of Δt, the emf e, induced across the ends
of the conductor is :
3. Know : The magnetic flux is given by : ɸ = B.A
Where Eemf is the electromotive force in volts and dɸ is the change of
magnetic flux in webers in a change of time dt in seconds and N is the
turn-loop.
1.1.2 - Fleming Left hand rule & Right hand rule
1. A current carrying conductor comes under a magnetic field, there
will be force acting on the conductor and on the other hand, if a
conductor is forcefully brought under a magnetic field, there will be an
induced current in that conductor.
2. In both of the phenomenon's, there is a relation between magnetic
field, current and force. This relation is directionally determined by
Fleming Left Hand rule and Right Hand rule respectively.
3. Directionally means these rules do not show the magnitude but
show the direction of any of the three parameters (magnetic field,
current, force) if the direction of other two are known. Fleming Left
Hand rule is mainly applicable for electric motor and Right Hand rule is
mainly applicable for electric generator.
Fleming Left hand rule VS Right hand rule
• First finger represents the direction of the
Field.
• The Second finger represents the direction of
the Current [conventional current, positive(+)
to negative(-).
• The Thumb represents the direction of the
Thrust or resultant Motion.
• FBI - moving from thumb to second finger.
• The thumb is the force F
• The first finger is the magnetic field B
• The second finger is the of current I
1.1.2 - Fleming Left hand & Right hand Rule
1. Each digit of your hand must be at
right angles to both of the other two
thumb
first finger
2. If the current is
reversed, the
second direction of motion
finger
motion
will change
field
3. Fleming Left Hand rule is mainly
applicable for electric motor
current
Field lines in the same direction cause repulsion, field lines in
opposite directions cause attraction
Field lines in the same direction cause repulsion, field lines in opposite
directions cause attraction
North Pole
Force
repulsion
attraction
North Pole
South Pole
attraction
repulsion Force
South Pole
The Right Hand Rule simply shows how a current-carrying wire generates
a magnetic field
• point your thumb in the direction
of the current and let your fingers
assume a curved position, the
magnetic field circling around the
wires flows in the direction in
which your four fingers point.
Fleming's right hand rule (for
generators). The appropriately-
handed rule can be recalled by
remembering that the letter "g"
is in "right" and "generator"
Right Hand Rule
Each digit of your hand must be at right
angles to both of the other two
North pole
+ B second
finger thumb
e
Velocity motion
current
-
L v
first finger
I field
If the motion is reversed, the polarity of EMF
South pole
will change and the current will be reversed
If the field is reversed, the polarity of EMF will
change again and the current will be reversed again
1.1.3 - Basic Construction DC Generators Consists Of Two Parts:
i. Moving parts - of the armature.
ii. Stationary part - consists of yoke (frame),
poles core and fields winding.
THREE FACTORS DETERMINE THE E.M.F IS
GENERATED IN THE ARMATURE.
i. The strength of the magnetic field, (φ)
ii. Number of conductors armature, (Z) Figure : DC Generator
iii. Armature speed rate, (N) Construction Basic
diagram.
PRINCIPLE OF OPERATIONS
This generator consists of a pair of poles
and a single coil is connected to a pair
of commutators and carbon brushes.
If the coil is rotated conductor coil means
cutting the magnetic field produced by the Figure : DC Generator
Construction Basic diagram.
main poles.
These cuts will generate E.M.F in the coil conductor. E.M.F produced
will be through the commutators and carbon brushes to the load
circuit.
Where is the commutator function is to convert from a.c to d.c.
1.1.4 - Main Part Of D.C Generator
DC Generator Construction
1.1.4 - Main Part Of D.C Generator
Yoke/frame Field pole/
kutub medan
Armature/
angkir
Carbon brush/
berus karbon
Commutator/
penukartertib
1.1.4 - Main Part Of D.C Generator
1.The outer frame of a dc machine is called as
yoke. It provide mechanical support for poles.
It provide protection to whole machine from
dust, moisture etc. Yoke is also called as frame.
2.Its carries the magnetic flux produced by the
field winding.
3.For small machine yoke is made of cast iron.
For large machine it is made of cast steel or
rolled steel.
Yoke/frame
1.1.4 - Main Part Of D.C Generator
Pole of a generator is an electromagnet.
Pole provides magnetic flux when field
winding is excited. When Current is
passed through field winding it electro
magnetize the poles which produce
necessary flux. It is connected in series
or shunt to from field winding.
Pole core or pole made of cast iron or
cast steel. It built of these laminations of
annealed steel. The laminations is done
Pole and field windings to reduce the power lose due to eddy
currents. Field winding - The material
used for field conductor is copper.
1.1.4 - Main Part Of D.C Generator
1. It convert a.c. to d.c.
2. It collects the current form armature
conductor and pass it load with the help
of brushes.
3. It is made of a large number of edge
shaped segments of hard drawn copper
and are insulated from each other by
Commutator/penukartertib thin layer of mica.
1.1.4 - Main Part Of D.C Generator
1. Brushes collect the current from
commutator and apply it to external
load.
2. Brushes are made of carbon or
graphite it is rectangular in shape.
Carbon brush/berus karbon
1.1.4 - Main Part Of D.C Generator
Armature core is the rotor of the
machine. It is cylindrical in shape with
slots to carry armature winding. The
armature is built up of thin laminated
circular steel disks for reducing eddy
current losses. Armature is keyed to
the shaft.
Armature conductor, are placed in this
slots. When armature winding is rotated
using prime mover, the magnetic flux
Armature/angkir and voltage gets induced in it Armature
winding is connected to external circuit.
1.1.4 - Main Part Of D.C Generator
ARMATURE WINDING: It is usually
a former wound copper coil which
rests in armature slots. The armature
conductors are insulated from each
other and also from the armature
core.
Armature winding can be wound by
one of the two methods; lap winding
or wave winding. Double layer lap or
wave windings are generally used. A
Armature/angkir double layer winding means that
each armature slot will carry two
different coils.
