JAWAHAR NAVODAYA

VIDYALAYA
KURNOOL
PHYSICS INVESTIGATORY PROJECT
A.C. Generator
Session:-2023-24

SUBMITTED BY:
M.RANGA SWAMY
Class- XII
Roll No:-19
 Contents

Certificate
Acknowledgment
Introduction
Principle of A.C. Generator
Construction of A.C. Generator
Theory
Circuit Diagram
Working of A.C. Generator
Expression for Instaneous e.m.f.
produced
Result
Applications of A.C. Generator
Bibliography
 This is to certify thatM.RANGA
SWAMYa student of Class XII has
successfully completed the project under
the guidance of Mr. RINKU SHRAMA(PGT
PHY),During the academic year 2019-20
in partial fulfillment of physics practical
examination conducted by CBSE.

Sub.Teacher Principal Examiner

 Acknowledgment

It would my utmost pleasure to

express my sincere thanks to my
physics teacher Mr.Rinku sharma in
providing a helping hand in this project.
His valuable guidance and support and
supervision all through this project are
responsible for attaining its present
form.
 Introduction
A.C. Generator means Alternating
current generator. It is a device which is
used to convert mechanical energy into
electrical energy.

A.C. generator forces electric current

to flow through an external circuit. The
source of mechanical energy may be a
reciprocating or turbine steam engine,
water falling through a turbine or
waterwheel, an internal combustion
engine, a wind turbine, a hand crank,
compressed air, or any other source of
mechanical energy.
Terminology
Electromagnetic generators fall into one of two
broad categories, dynamos and alternators.
 Dynamos generate pulsing direct current through
the use of a commutator.
 Alternators generate alternating current.

Mechanically, a generator consists of a rotating part

and a stationary part which together form a magnetic
circuit:
 Rotor: The rotating part of an electrical machine.
 Stator: The stationary part of an electrical
machine, which surrounds the rotor.One of these
parts generates a magnetic field, the other has a
wire winding in which the changing field induces
an electric current:
 Field winding or field (permanent) magnets:
The magnetic field-producing component of an
electrical machine. The magnetic field of the
dynamo or alternator can be provided by either
wire windings called field coils or permanent
magnets. Electrically-excited generators include
 an excitation system to produce the field flux. A
generator using permanent magnets (PMs) is
sometimes called a magneto.

ARMATURE:
The power-producing component of an electrical
machine. In a generator, alternator, or dynamo,
the armature windings generate the electric
current, which provides power to an external
circuit.
The armature can be on either the rotor or the stator,
depending on the design, with the field coil or
magnet on the other part.
Faraday disk generator

The operating principle of electromagnetic

generators was discovered in the years of 1831–
1832 by Michael Faraday. The principle, later
called Faraday's law, is that an electromotive force is
generated in an electrical conductor which encircles
a varying magnetic flux.
He also built the first electromagnetic generator,
called the Faraday disk; a type of homopolar
generator, using a copper disc rotating between the
poles of a horseshoe magnet. It produced a
small DC voltage.
This design was inefficient, due to self-cancelling
counterflows of current in regions of the disk that
were not under the influence of the magnetic field.
While current was induced directly underneath the
magnet, the current would circulate backwards in
regions that were outside the influence of the
magnetic field. This counterflow limited the power
output to the pickup wires and induced waste
heating of the copper disc. Later homopolar
generators would solve this problem by using an
array of magnets arranged around the disc
perimeter to maintain a steady field effect in one
current-flow direction.
Another disadvantage was that the
output voltage was very low, due to the single
current path through the magnetic flux.
Experimenters found that using multiple turns of wire
in a coil could produce higher, more useful voltages.
Since the output voltage is proportional to the
number of turns, generators could be easily
designed to produce any desired voltage by varying
the number of turns. Wire windings became a basic
feature of all subsequent generator designs.
Principle of A.C. Generator

It is based on the principle of electro-

magnetic induction,
i.e., whenever amount of magnetic flux
linked with a coil changes, an e.m.f. is
induced in the coil.
The direction of current induced is given
by Fleming’s right-hand rule.

Construction of A.C. Generator

The A.C. Generator is consist of four main parts :

(1) THE COIL (ARMATURE) :

A rectangular coil ABCD consist of a large number
of turns of copper bound over a soft iron core is called
armature. The soft iron core is used to increase the
magnetic flux.

(2) MAGNETIC FIELD :

It is usually a permanent sponge magnet having
concave poles. The armature is rotated of a magnet so
that axis of the armature is perpendicular to magnetic
field lines.

(3) SLIP RINGS :

Slip rings are the magnetic rings, which are connected
to the terminal of the armature. These rings are
rotated with the coil and these are used to draw the
current from the generator.
(4) BRUSHES :The brushes B1 & B2 just touches the
slip rings. They are not rotating with the coil and these
brushes lead to the output of load resistance.
 Theory
1. The strong magnetic field is produced by a current flow
through the field coil of the rotor.

2. The field coil in the rotor receives excitation through the

use of slip rings and brushes.

3. Two brushes are spring-held in contact with the slip rings

to provide the continuous connection between the field coil
and external circuit.

4. The armature is contained within the windings of the

stator and is connected to the output.

5. Each time the rotor makes one complete revolution, one

complete cycle of AC is developed.

6. A generator has many turns of wire wound into the slots

of the rotor.

7. The magnitude of AC voltage generated by an AC

generator is dependent on the field strength and speed of
the rotor.

8. Most generators are operated at a constant speed;

therefore, the generated voltage depends on field excitation
or strength.
Circuit Diagram
 Working of an A.C. Generator

The coil is rotated in the anti-clockwise

direction. In the first half rotation the arm AB is
moving outward and CD is moving inward. So
the e.m.f. is induced in the arm AB from A to B.
And in the arm CD from C to D. After half
rotation (in the second half). The arm CD is
moving outward and AB is moving inward. In
this time current is induced in arm CD from D to
C. And in arm AB from B to A. In the second-half
rotation, the current direction is changing so in
this generator AC is produced.
c
 Expression for Instaneous
e.m.f. produced

Let position of the coil at any time t.

It's making angle θ with vertical. If w is
uniform angular speed of the coil.

Then, θ =ωt

B be the strength of 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 :

Φ = nBA Cosθ = nBA Cos ωt.

Differentiate w.r.t. time:-

Maximum value of e.m.f. So 𝜺,

ε = ε° sin(𝜔𝑡)
Result:-
Hence, maximum value of instantaneous e.m.f. in an AC
Generator is given by

𝜺 = 𝜺° sin(𝝎𝒕)

Equivalent circuit
An equivalent circuit of a generator and load is
shown in the adjacent diagram. The generator is
represented by an abstract generator consisting of
an ideal voltage source and an internal impedance.

The generator's and parameters can be

determined by measuring the winding resistance
(corrected to operating temperature), and measuring
the open-circuit and loaded voltage for a defined
current load.
This is the simplest model of a generator, further
elements may need to be added for an accurate
representation. In particular, inductance can be
added to allow for the machine's windings and
magnetic leakage flux,[23] but a full representation can
become much more complex than this
Applications of A.C. Generator
1. Aircraft auxiliary power generation, wind
generators, high-speed gas turbine generators.

2. Hybrid electric vehicle (HEV) drive systems,

automotive starter generators.

3. An ac generator, or 'alternator', is used to

produce ac voltages for transmission via the grid
system or, locally, as portable generators.

4. All of our household appliances run on ac current.

Ex: Refrigerator, washing machines, oven, lights,
fan, etc.

5. The main advantage of AC is ease of power

distribution.
It is more efficient to use high voltage to distribute
power, but it is not safe to have high voltage at
home. It is easy to step up (and step down) AC
voltage using a transformer.
 Bibliography

• CBSE Lab manual

• Help of Physics Teacher
• NCERT Textbook
• Websites:-
www.google.com
www.wikipedia.com