PHYSICS
PROJECT
UNDERTHEGUIDANCEOF: SUBMITTEDBY:
MR. D.P. SRIVASTAVA SUJAY KUMAR LAL
ROLL NO :
CLASS: 12th
BATCH: 2015-16

CERTIFICATE
This is to certify that Master Sujay Kumar Lal
student of class 12 of Central Academy Senior
Secondary School successfully completed his
project under my guidance.
This project is submitted for evaluation as a part
of CBSE curriculum examination for year 2015-
16.
TEACHER PRINCIPAL
MR. D.P. SRIVASTAVA Mrs. MALA
SAXENA

ACKNOWLEDGEMENT
I have taken efforts in this project. However, it
would not have been possible without the kind
support of my family & friends. I would like to extend
my sincere thanks to all of them.
I am highly indebted to the teacher incharge Mr.
D.P. Srivastava for her guidance and constant
supervision as well as for providing necessary
information regarding the project and also for her
support in completing the project.
I would like to express my gratitude towards my
parents for their kind co-operation and encouragement
which help me in the completion of this project.
My thanks and appreciation also go to my classmates
in developing the project and to the people who have
helped me out with their abilities.
THANK YOU

AC GENERATOR
What is Ac generator?
The Alternating Current Generator, an
electric generator, or dynamo, is a
device which converts mechanical
energy into electrical energy. The
simplest practical generator consists
of a rectangular coil rotating in a
uniform magnetic field. The magnetic
field is usually supplied by a
permanent magnet.
Principle :
A.C. generators or alternators (as
they are usually called) operate on
the same fundamental principles
of electromagnetic induction as D.C.
generators.
Alternating voltage may be
generated by rotating a coil in the
magnetic field or by rotating a
magnetic field within a stationary
coil. The value of the voltage
generated depends on-

 the number of turns in the
coil.
 strength of the field.
 the speed at which the coil or
magnetic field rotates.
Components of AC Generator
 Field
 Armature
 Prime mover
 Rotor
 Stator
 Slip ring
Field:
The field in an AC generator consists
of coils of conductors within the
generator that receive a voltage from
a source. (called excitation) and
produce a magnetic flux. The
magnetic flux in the field cuts
the armature to produce a
voltage. This voltage is ultimately
the output voltage of the AC
generator.

Armature:
The armature is the part of an
AC generator in which voltage is
produced. This component
consists of many coils of wire
that are large
enough to carry the full-
load current of the generator.
Prime Mover:
It is the component that is used to
drive the AC generator. The prime
mover maybe any type of rotating
machine, such as a diesel engine, a
steam turbine, or a motor.
Rotor:
The rotor of an AC generator is the
rotating component of the generator,
The rotor is driven by the
generator’s prime mover, which may be
a steam turbine, gas turbine, or
diesel engine.
Stator:
The stator of an AC generator is the
part that is stationary (refer to
Figure 1). Like the rotor, this
component may be the armature or the

field, depending on the type of
generator. The stator will be the
armature if the voltage output is
generated there; the stator will be
the field if the field excitation is
applied there.
Slip Rings:
Slip rings are electrical
connections that are used to transfer
power to and from the rotor of an AC
generator.
Working
The working principle of an
alternator or AC generator is similar
to the basic working principle of a
DC generator.

Above figure helps in
understanding how an alternator or AC
generator works. According to the
Faraday's law 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.

Losses in Ac generator
The load current flows through the
armature in all AC generators. Like
any coil, the armature
has some amount of resistance and
inductive reactance. The combination
of these make up what is known as the
internal resistance, which causes a
loss in an AC generator. When the
load
current flows, a voltage drop is
developed across the internal
resistance. This voltage drop
subtsracts from the output voltage
and, therefore, represents generated
voltage and power that is
lost and not available to the load.
The voltage drop in an AC generator
can be found using
Equation-
Voltage drop = IaRa + IaXla
Where.
Ia = armature current
Ra = armature resistance
XLa = armature inductive
reactance

The three losses found in an AC
generator are:
 Internal voltage drops due to the
internal resistance and impedance
of the generator
 Hysteresis losses
 Mechanical losses
HysteresisLosses–
Hysteresis losses occur when iron
cores in an AC generator are subject
to effects from a
magnetic field. The magnetic domains
of the cores are held in alignment
with the field in
varying numbers, dependent upon field
strength. The magnetic domains
rotate, with respect to
the domains not held in alignment,
one complete turn during each
rotation of the rotor. This
rotation of magnetic domains in the
iron causes friction and heat. The
heat produced by this

friction is called magnetic
hysteresis loss.
Mechanical Losses-
Rotational or mechanical losses can
be caused by bearing friction, brush
friction on the
commulator, and air friction (called
windage), which is caused by the air
turbulence due to
armature rotation. Careful
maintenance can be instrumental in
keeping bearing friction to a
minimum. Clean bearings and proper
lubrication are essential to the
reduction of bearing friction.
Brush friction is reduced by
ensuring: proper brush seating,
proper brush use, and maintenance
of proper brush tension. A smooth and
clean commutator also aids in the
reduction of brush
friction. In very large generators,
hydrogen is used within the generator
for cooling; hydrogen,
being less dense than air, causes
less windage losses than air.

Efficiency -
Efficiency of an AC generator is the
ratio of the useful power output to
the total power input.
Because any mechanical process
experiences some losses, no AC
generators can be 100 percent
efficient. Efficiency of an AC
generator can be calculated using
Equation.
Efficiency =
𝑂𝑢𝑡𝑝𝑢𝑡
𝐼𝑛𝑝𝑢𝑡
x 100

BIBLIOGRAPHY
www.slideshare.com
www.mycbseguide.com
www.ask.com
NCERT (textbook)
www.google.com
www.yahooanswer.com
www.electricalessay.com