2. AC GENERATOR
It is also called dynamo or alternator.
It converts mechanical energy into electrical
energy.
It produces a current that alternates or changes its
direction regularly after a fixed interval of time.
It operates through the interaction between a
magnetic field and coil.
It works on the principal of ELECTROMAGNETIC
INDUCTION.
3. PRINCIPLE OF AC GENERATOR
The working of an AC GENERATOR is based
on the principle of ELECTROMAGNETIC
INDUCTION.
When a coil is rotated in a uniform magnetic
field with its axis perpendicular to the
magnetic field ,the magnetic flux linked with
the coil changes and an induced EMF and a
current is set up in the coil.
4.
5. COMPONENTS OF AC GENERATOR
FIELD MAGNET
ARMATURE
SLIP RINGS
BRUSHES
SOURCE OF ENERGY/PRIME MOVER
6. FIELD MAGNET
It is a horse shoe shaped permanent magnet or a
powerful electromagnet.
It produces a strong magnetic field in the region
between its pole pieces.
7. ARMATURE
It consists of a rectangular coil having a large number of
turns of insulated copper wire wound on a soft iron
cylindrical core.
The core is laminated to avoid loss due to eddy currents.
It can be rotated in the magnetic field of the field about an
axis perpendicular to field.
8. Slip rings
Two ends of armature coil are connected to two
coaxial brass ring called slip rings.
Slip rings are rigidly fixed to same shaft which is
used to rotate the coil.
As the armature coil rotates the slip rings also rotates
about the same axis of rotation.
9. Brushes
Two graphite or flexible metallic rods called brushes are
lightly pressed against slip rings.
The brushes remain fixed in their positions and maintain
sliding contacts with the rotatable slip rings.
Through brushes the current induced in the armature coil is
fed to the external circuit by the means of line wires.
10. Source of energy
It is the component which is used to drive
the AC Generator.
It can be any type of rotating machine ,such
as diesel engine ,turbine or a motor.
The rotational kinetic energy of the energy
source is converted into electrical energy by
the AC Generator.
13. When the armature rotates between the poles of a magnet
upon an axis perpendicular to the magnetic field ,the flux
linked with it changes continuously .Due to this an emf is
induced in the armature .this produces an electric current
through the galvanometer and the slip rings and brushes.
14. Generating EMF
1- when the coil is
perpendicular to the field the
induced emf is the greatest.
2- when the coil is parallel to
the field the induced emf is
zero.
3 – if the coil is rotated at
constant speed then the
induced emf will vary
sinusoidally with the same
frequency as the rotation.
15. Induced EMF
.The flux linkage of a coil of N turns and cross section
area A in a uniform magnetic field B is given by :
Φ=NBA
.
If the coil is rotating then the flux linkage when the
normal to the plane of the coil makes angle θ to the
field becomes:
Φ=NBAcosθ
16. The induced emf is therefore given by the rate of
change of flux linkage :
ε =-dΦ/dt =-d(BANcos θ )/dt
It can be shown that this is same as:
ε =BANsinθ dθ /dt
Where Δ θ /Δt is the angular velocity( ω)in rad/s
Therefore ,
ε =BAN(sin ωt ) ω
17. The maximum EMF is therefore when sin ωt=1
emf0=BANω(maximum emf)
18. Efficiency
Efficiency of an ac generator is the ratio of
the useful power output to the total power
input .
EFFICIENCY = OUTPUT/INPUT*100
No ac generators can be 100 % efficient .
19. Applications
Aircraft auxiliary power generation ,wind generators,
high speed gas turbine generators.
Hybrid electric vehicle(HEV) drive systems
,automotive starter generators .
Used to produce ac voltage for transmission via the
grid system or locally as portable generators.
