Download What is the principle of AC Generator?

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PREPARED BY –
S. K. MISHRA
P G T (PHYSICS)
JNV NONGSTOIN
STUDENTS WILL LEARN ABOUT CONSTRUCTION, THEORY
AND WORKING OF A. C. GENERATOR.
USE OF GENERATOR IN DIFFERENT
APPLICATIONS.
DIFFERENCE BETWEEN A. C. AND D.
C. GENERATOR.
Students have knowledge of
1. Magnetic flux
2. Flemegin’s right hand rule
3. Faraday’s law of electromagnetic
induction
4. Induced current .
 A.C. CONSISTS OF FOLLOWING
PARTS –
 FIELD COILS
 ARMATURE COIL
 SOFT IRON CORE
 SLIP RINGS
 CARBON BRUSH
BEBARINGS
DIAGRAM
• 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 the conductors as they are
rotating (Figure 3). The strong magnetic
field is produced by a current flow through
the field coil of the rotor.
Consider a coil of wire rotating in a
uniform magnetic field, of flux density,
B, as shown below.
Fleming’s right hand rule
When the coil is in the position
shown in the diagram, side 2 is
moving down and side 1 is
moving up. We can use
Fleming’s right hand rule to
decide that end q will (at that
instant) be the positive terminal
of the generator.
When the coil has rotated through half
a turn, end p will be the positive
terminal.
Therefore, a coil of wire rotating in a
magnetic field has an alternating emf
induced in it.
To connect the coil to a light bulb (or
any other component) brushes made
of carbon make contact with slip rings
made of brass, as shown in the next
diagram.
• Consider a coil having N turns,
rotating in a magnetic field of
uniform flux density, B. The area of
the coil is A and the angle between
the normal to the plane of the coil
and the field is a.
• flux linkage = NABcosa
• If the angular velocity is w, then a =
wt, so the flux linkage at any time,
t, is given by
• flux linkage = NABcoswt
Therefore, the induced emf at any instant
is given by
Where
It can easily be shown that the
slope of a graph of cos wt against t
is equal to –wsin wt so the induced
emf is given by
Induced E.M.F.Vs Time Graph
• 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, or strength.
•The frequency of the generated
voltage is dependent on the number of
field poles and the speed at which the
generator is operated, as indicated.
•AC Generator
• The turning of a coil in a magnetic field
produces motional emfs in both sides of
the coil which add. Since the component
of the velocity perpendicular to the
magnetic field changes sinusoidally with
the rotation, the generated voltage is
sinusoidal or AC.
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GENERATION OF INDUCED
CURRENT IN SINGLE COIL
•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 rings to provide the
continuous connection between
the field coil and the external
•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.
Magnetic flux is the product of the average
magnetic field times the perpendicular area
that it penetrates. It is a quantity of
convenience in the statement of Faraday's
Law and in the discussion of objects like
transformers and solenoids. In the case of an
electric generator where the magnetic field
penetrates a rotating coil, the area used in
defining the flux is the projection of the coil
area onto the plane perpendicular to the
magnetic field.
•It is used for generation of
electricity for domestic as well as
commercial purpose .
•In all types power plants only
• A. C. generators are used .
•The principle of working of A. C.
motors are reciprocal to that of
•A. C. generators .
HYDRO-ELECTRICITY
GENERATION
HYDRO-ELECTRICITY
GENERATION
SUMMARY
When a coil of N turns, rotates
in Uniform magnetic field with
constant angular velocity
ω.the induced current
developed in the coil is taken
as out put through slip rings.
QUERRY
?
1. What is function of field coils?
2. What is the principle of A.C. Generator?
3. How can you convert A.C. Generator in to
D.C. Generator?
4. Why radial magnetic field is necessary?
1. Draw labeled diagram of A.C. Generator.
2. Write theory and working of A.C. Generator.
3. Draw labeled diagram of D.C. Generator.
4. Write two names each of thermal, hydro, nuclear
and wind power stations in India.
BIBILOGRAPHY
The following reference Books and web sites are
consulted for preparation of this lesson plan1. Concept of Physics
By- H.C. Verma
2. Fundamentals of Physics
By-D.Holliday&
R.Resinik
3.http:micro.magnet.fsu.edu./electromag/java/gen
erator/ac.html
4.http://www.walter-fendt.de/ph11e/generator
_e.htm