electrical michenery

1. SubmittedTo:

2. 1. DC Motor
1.1. Defination:
The DC motor is the motor which converts the direct current into the mechanical
work. It works on the principle of Lorentz Law, which states that “the current
carrying conductor placed in a magnetic and electric field experience a force”. And
that force is the Lorentz force.
1.2. Types:
There are 4 major types of DC motor and they are,
 Series DC Motor
 Permanent Magnet DC Motor
 Shunt/Parallel DC Motor
 Compound DC Motors
1.3. Construction:
Before understanding the working of DC motor first, we have to know about their
construction. There are two main parts of the DC motor.
 Armature
 Stator
The rotating part is the armature and the Stator is their stationary part. The
armature coil is connected to the DC supply.
Figure 1

3. 1.4Working:
A DC motor is an electrical machine which converts electrical energy into mechanical energy.
The basic working principle of the DC motor is that whenever a current carrying conductor
places in the magnetic field, it experiences a mechanical force.
2.DC Generator:
2.1. Defination:
A DC generator or direct current generator is one kind of electrical machine, and the main
function of this machine is to convert mechanical energy into DC (direct current) electricity. The
energy alteration process uses the principle of energetically induced electromotive force.
2.2.Construction:
A DC generator is also used as a DC motor without changing its construction. Therefore, a DC
motor otherwise a DC generator can be generally called a DC machine. The construction of a 4-
pole DC generator is shown below. This generator comprises of several parts like yoke, poles &
pole shoes, field winding, an armature core, armature winding, commutator & brushes. But the
two essential parts of this device are the stator as well as the rotor.
2.2.1.Stator
The stator is an essential part of the DC generator, and the main function of this is to provide
the magnetic fields where the coils spin. This includes stable magnets, where two of them are
with reverse poles facing. These magnets are located to fit in the region of the rotor.

4. 2.2.2. Rotor or Armature Core
Rotor or armature core is the second essential part of the DC generator, and it includes slotted
iron laminations with slots that are stacked to shape a cylindrical armature core. Generally,
these laminations are offered to decrease the loss because of the eddy current.
2.2.3. Armature Windings
The armature core slots are mainly used for holding the armature windings. These are in a
closed circuit winding form, and it is connected in series to parallel for enhancing the sum of
produced current.
2.2.4. Yoke
The external structure of the DC generator is Yoke, and it is made with cast iron otherwise steel.
It gives the necessary mechanical power for carrying the magnetic-flux given through the poles.
2.2.5. Poles
These are mainly used to hold the field windings. Usually, these windings are wound on the
poles, & they are connected in series otherwise parallel by the armature windings. In addition,
the poles will give joint toward the yoke with the welding method otherwise by using screws.
2.2.6. Pole Shoe
The pole shoe is mainly utilized for spreading the magnetic flux as well as to avoid the field coil
from falling.
2.2.7. Commutator
The working of the commutator is like a rectifier for changing AC voltage to the DC voltage
within the armature winding to across the brushes. It is designed with a copper segment, and
each copper segment is protected from each other with the help of mica sheets. It is located on
the shaft of the machine.
2.2.8. Brushes
The electrical connections can be ensured between the commutator as well as the exterior load
circuit with the help of brushes.

5. 2.3. Types:
2.4. Working:
The working principle of the DC generator is based on Faraday’s laws of electromagnetic
induction. When a conductor is located in an unstable magnetic field, an electromotive force
gets induced within the conductor. The induced e.m.f magnitude can be measured from the
equation of the electromotive force of a generator.
If the conductor is present with a closed lane, the current which is induced will flow in the lane.
In this generator, field coils will generate an electromagnetic field as well as the armature
conductors are turned into the field. Therefore, an electromagnetically induced electromotive
force (e.m.f) will be generated within the armature conductors. The path of induced current will
be provided by Fleming’s right-hand rule.
3.AC Motor:
3.1. Defination:
An AC motor is an electric motor driven by an alternating current (AC).
3.2. Construction:
The AC motor commonly consists of two basic parts,
 an outside stator having coils supplied with alternating current to produce a rotating
magnetic field, and an inside rotor attached to the output shaft producing a
 second rotating magnetic field. The rotor magnetic field may be produced by permanent
magnets, reluctance saliency, or DC or AC electrical windings.

6. 3.3. Working:
It works on the principle of Lorentz force equation I,e whenever a current-carrying conductor is
placed in the magnetic field it exhibits some force in it. The working of a normal AC machine
with the rotating armature and stationary field winding is shown in the figure below.
3.5. Types:

7. 4. AC Generator
4.1 Defination:
AC generator is a machine that converts mechanical energy into electrical energy. The
AC Generator’s input supply is mechanical energy supplied by steam turbines, gas
turbines and combustion engines. The output is alternating electrical power in the form
of alternating voltage and current.
4.2.Construction:
4.2.1.Field:
The field consists of coils of conductors that receive a voltage from the source and
produce magnetic flux. The magnetic flux in the field cuts the armature to produce a
voltage. This voltage is the output voltage of the AC generator
4.2.2.Armature:
The part of an AC generator in which the voltage is produced is known as an armature.
This component primarily consists of coils of wire that are large enough to carry the full-
load current of the generator.
4.2.3.Prime Mover:
The component used to drive the AC generator is known as a prime mover. The prime
mover could either be a diesel engine, a steam turbine, or a motor.
4.2.4.Rotor:
The rotating component of the generator is known as a rotor. The generator’s prime
mover drives the rotor.
4.2.5.Stator:
The stator is the stationary part of an AC generator. The stator core comprises a
lamination of steel alloys or magnetic iron to minimise the eddy current losses.
4.2.6.Slip Rings:
Slip rings are electrical connections used to transfer power to and fro from the rotor of
an AC generator. They are typically designed to conduct the flow of current from a
stationary device to a rotating one.
4.3.Working of an AC Generator
When the armature rotates between the poles of the magnet upon an axis
perpendicular to the magnetic field, the flux linkage of the armature changes
continuously. As a result, an electric current flows through the galvanometer and the
slip rings and brushes. The galvanometer swings between positive and negative values.
This indicates that there is an alternating current flowing through the galvanometer. The
direction of the induced current can be identified using Fleming’s Right Hand Rule.

8. 5. Diffrences between AC and DC machines
5.1 Diffrence between AC motor and DC motor:
AC Motor DC Motor
AC motors are available in two-
phase type, single-phase or three
phases.
All DC motors are single phase.
In AC motors Armatures don’t rotate
with the continuous rotation of
magnetic fields.
In DC motors, the armature rotates
while the magnetic field rotates.
Repairing is not costly. Repairing is quite costly
Have a longer life span. Have a shorter lifespan.
AC motors require effective starting
equipment like a capacitor to start
operation.
DC motors do not require any
external help to start operation.
Have three input terminals. Have two input terminals.
AC motors are late responsive when
there is a change in the load.
DC motors are fast responsive to the
change in load.

9. 5.2. Diffrence between AC and DC generators:
AC Generator DC Generator
AC generator is a mechanical device that
converts mechanical energy into AC
electrical power.
DC generator is a mechanical
device that converts mechanical
energy into DC electrical power
In an AC generator, the electrical current
reverses direction periodically.
In a DC generator, the electrical current
flows only in one direction.
In an AC generator, the coil through
which the current flows is fixed while the
magnet moves. The construction is
simple and costs are less.
In a DC generator, the coil through
which the current flows rotate in a fixed
field. The overall design is very simple
but construction is complex due to
commutators and slip rings.
AC generator does not have
commutators.
DC generators have commutators to
make the current flow in one direction
only.
AC generators have slip-rings. DC generators have commutators.
Since slip-rings have a smooth and
uninterrupted surface, they do not wear
quickly and are highly efficient.
Both brushes and commutators of a DC
generator wear out quickly and thus are
less efficient.
As the brushes have high efficiency, a
short circuit is very unlikely.
Since the brushes and commutators
wear out quickly, sparking and short
circuit possibility is high.