Physcis Ac Generator Report

PHYSICS
PROJECT
AC GENERATOR
INTRODUCTION
An electric generator is a device that

converts mechanical energy to electrical
energy. A generator forces electric current
to flow through an external circuit. The
mechanical reciprocating source energy
may or be of a turbine steam engine, water
falling through turbine or water wheel, an
internal combustion engine, a wind turbine,
a hand crank, compressed air, or any other
source of mechanical energy. Generators
provide nearly all of the power for electric
power grids.
THEORY OF OPERATION
A simple AC generator consists of, (a) A

strong magnetic field,
(b) Conductors that rotate through that
magnetic field, and
(c) A means by which a continuous connection
is provided to conductors as they are rotating.
The strong magnetic field is produced by a
current flow through the field coil of the rotor.
The field coil in the rotor receives excitation
through the use of slip rings and brushes. Two
brushes are spring-held in contact with the slip
to provide the continuous connection between
the field coil and the external excitation circuit.
The armature is contained within the windings
of the stator and is connected to the output.
Each time the rotor makes one complete
revolution, one complete cycle of AC is
developed. A generator has many turns of wire
wound into the slots of the rotor. The
magnitude of AC voltage generated by an AC
generator is dependent on the field strength
and speed of the rotor. Most generators are
operated at a constant speed; therefore, the
generated voltage depends on field excitation,
strength.
WORKING
An alternator is an electrical machine which
converts mechanical energy into alternating
electric energy. They are also known as
synchronous generators.
How Does An AC Generator Work?

an The working principle of alternator or AC
generator is similar to the basic working
principle of a DC generator.
Above figure helps you understanding how an
alternator or AC generator works. the
Faraday's law According to of electromagnetic
induction, whenever a conductor moves in a
magnetic field EMF gets induced across the
conductor. If the close path is provided to the
conductor, induced emf causes current to flow
in the circuit.Now, see the above figure. Let
the conductor coil ABCD is placed in a
magnetic field. The direction of magnetic flux
will be form N pole to S pole. The coil is
connected to slip rings, and the load is
connected through brushes resting on the slip
rings.
Now, consider the case 1 from above figure.
The coil is rotating clockwise, in this case the
direction of induced current can be given by
Fleming's right hand rule, and it will be along
A-B-C-D.
As the coil is rotating clockwise, after half of
the time period, the position of the coil will be
as in second case of above figure.
In this case, the direction of the induced
current according to Fleming's right hand rule
will be along D-C-B-A.It shows that, the
direction of the current changes after half of
the time period that means we get an
alternating current.
CONSTRUCTION
Main parts of the alternator, obviously,

consists of stator and rotor. But, the unlike
other machines, in most of the alternators,
field exciters are rotating and the armature
coil is stationary.
Stator: Unlike in DC machine stator of an
alternator is not serve path for meant to
magnetic flux. Instead, the stator is used
for holding armature winding. The stator
core is made up of lamination of steel
alloys or magnetic iron, to minimize the
eddy current losses.
Why Armature Winding Stationary Is An

Alternator?
At high voltages, it easier to insulate
stationary armature winding, which may be
as high as 30 kV or more.The high voltage
output can be directly taken out from the
stationary armature. Whereas, for a rotary
armature, there will be large brush contact
drop at higher voltages, also sparking at
the brush surface will occur. the Field
exciter winding is placed in rotor, and the
low dc voltage can be transferred safely.
The armature winding can be braced well,

so as to prevent deformation caused by the
high centrifugal force.
Rotor: There are two types of rotor used in
an AC generator / alternator: (I) Salient and
(II) Cylindrical type
1. Salient pole type: Salient pole type rotor
is used in low and medium speed
alternators. Construction of AC generator
of salient pole type rotor is shown in the
figure above. This type of rotor consists of
large number of projected poles (called
salient poles), bolted on a magnetic wheel.
These poles are also laminated to minimize
the eddy current losses. Alternators
featuring this type of rotor are large in
diameters and short in axial length.
2. Cylindrical type: Cylindrical type rotors
are used in high speed alternators,
especially in turbo alternators. This type of
rotor consists of a smooth and solid steel
cylinder having slots along its outer
periphery. Field windings are placed in
these slots.The DC supply is given to the
rotor winding through the slip rings and
brushes arrangement.
EFFICIENCY
Efficiency of an AC generator is the ratio of
the useful power output to the total power
input Because any mechanical experiences
process no AC some losses, generators
can be 100% efficient.
Efficiency of an AC generator can be

calculated using equation,
Efficiency = (output/input) x 100
Expression for instantaneous E.M.F
produced:
Let position of the coil at any time t.

It makes angel q with vertical.
If w is uniform speed of the coil.
Then q=wt
B be the strength of the magnetic field n be

the number of turns in the coil and A area
of the coil then magnetic flux with the coil
in this position is given by:
F=nBA Cos q = nBA Cos wt Diffrentiate

w.r.t. to time
=nBA (-Sin wt) w
=-nBA w Sin wt
e=-(-nBA w Sin wt)
Maximum values of e.m.f. say E
e=E Sin wt
BIBLIOGRAPHY
www.nuclearpowertraining.tpub.com
www.slideshare.net woodengenerator.com
www.sciencing.com
www.allprojectreports.com
www.electricaleasy.com

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PHYSICS

An electric generator is a device that

A simple AC generator consists of, (a) A

How Does An AC Generator Work?

Main parts of the alternator, obviously,

Why Armature Winding Stationary Is An

The armature winding can be braced well,

Efficiency of an AC generator can be

Let position of the coil at any time t.

If w is uniform speed of the coil.

B be the strength of the magnetic field n be

F=nBA Cos q = nBA Cos wt Diffrentiate

e=-(-nBA w Sin wt)

Maximum values of e.m.f. say E

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