Dayawati modi public school PHYSICS PROJECT- AC GENERATOR
Submitted to Mrs P.K. Sharma
Submitted by Sakar singhal XII-D R9
CERTIFICATE This
is
certify that
sakar
singhal of class XII-D 'Science of Dayawati
modi
Modinagar
has
public
school,
prepared
this
Physics project ac generator In accordance with guide lines followed by C.B.S.E., New Delhi. She
has
worked
as
per
the
instruction and certifies that this process
is
unique
and
not
copied. Teacher's Signature Mr. P.K. Sharma
Physics Teacher
INTRODUCTION An electric
generator is
converts mechanical
a
device
energy to electrical
that
energy.
A
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. Generators provide nearly all of the power for electric power grids
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 the
slip
rings
connection between
to the
in contact
provide
the
field
coil
with
continuous and
the
external excitation 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.
WORKING Principle : The electrical generator works on the principle that when a straight conductor is moved in a magnetic field, then current is induced in the conductor. The direction of this induced current is given by Fleming's right hand rule.
Construction of AC generator : It consists of a rectangular coil ABCD which can be rotated repidly between N and S poles of a strong horse-shoe shaped magnet having radial ends. The coil is made of a large number of turns of insulated copper wire. The ends A
and D of the coil are connected to slip rings R1 and R2. As the slip rings R1 and R2 rotate with the coil, the two carbon brushes B1 and B2 keep contact with them. Outer ands of the two brushes B1 and B2 are connected to the galvanometer to show the flow of the current in the given external circuit. Working : When the coil starts rotating with the arm AB moving up and the arm CD moving down, cutting the magnetic lines of force, then according to Fleming's right hand rule and induced current is set up in these arms along the direction of AB and CD. So an effective induced current flowing in the direction of ABCD is obtained. If there are large number of turns in the coil, the current generated in each turn adds upto give a large quantity of current through the coil. After half rotation of the coil, its arm CD starts moving up and AB moving down. As a result, the direction of the induced
currents gets reversed in the coil in the direction of DCBA. Thus after every half rotation the polarity of the current in the respective arm changes. Such a current, which changes its direction after equal intervals of time, is called to get a direct current a split ring type commutator must be used in place of slip ring commutator.
USES 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 runs on ac current. Ex: Refrigerator, washing machines, oven, lights, fan etc.
EFFICIENCY Expression for Instantaneous e.m.f. Produced: Let position of the coil at any time t. It make angle q with vertical. If w is uniform angular speed of the coil. Then ⱷ= wt 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: ⱷ = nBA Cos wt. Differentiate w.r.t. time = nBA (-Sin wt) w = -nBA w Sin wt e = - (-nBA w Sin wt) maximum value of e.m.f. say E0 e = E0 Sin wt.
1) Efficiency of an AC generator is the ratio of the useful power output to the total power input.
2) Because
any
mechanical
process
experiences
some losses, no AC generators can be 100 percent efficient.
3) Efficiency of an AC generator can be calculated using Equation. 4) Efficiency =(Output /Input ) × 100
